What is Flash Memory? How Flash Memory Works What two functions are characteristics of flash memory.

It has become indispensable in mobile devices (PDAs, tablets, smartphones, players). Based on flash memory, USB flash drives and memory cards for electronic devices (SD, MMC, miniSD, etc.) have been developed.

Definition 1

Flash memory(Flash Memory) - solid-state semiconductor non-volatile and rewritable memory.

It is possible to read information from flash memory a large number of times within the lifetime of the drive (from $10$ years), but the number of write processes is limited (about $100 \ 000$ rewriting cycles).

Flash memory is considered a more reliable type of storage medium, because. does not contain moving mechanical parts (as, for example, in a hard drive).

Advantages of flash memory:

• high speed of data access;
• low power consumption;
• vibration resistance;
• ease of connection to a PC;
• compact dimensions;
• cheapness.

Disadvantages of flash memory:

• limited number of write cycles;
• sensitivity to electrostatic discharge.

History of flash memory

Flash memory was first invented in $1984.

The name "flash" comes from the English "flash", because. the process of erasing data was like a flashlight.

In $1988$, the first commercial NOR-type flash processor was released. The following year, the NAND flash memory architecture was developed, which featured faster write speeds and a smaller circuit area.

Principle of operation

The storage unit cell is a floating gate transistor that can hold electrons (charge) is the storage unit cell in flash memory. Based on the transistor, the main types of NAND and NOR flash memory have been developed. The principle of operation is based on the change and registration of an electric charge in an isolated area ("pocket") of a semiconductor structure.

Figure 1. NOR memory architecture

Figure 2. NAND architecture

Flash memory manufacturers use $2$ types of memory cells:

• MLC(Multi-Level Cell - multi-level memory cells) - more capacious cells and cheaper, but are characterized by a long access time and a small number of write / erase cycles (about $ 10 \ 000 $);
• SLC(Single-Level Cell - single-level memory cells) - cells with a shorter access time and the maximum number of write / erase cycles ($ 100 \ 000 $).

Figure 3. The main elements of a USB flash drive: $1$ - USB connector, $2$ - controller, $3$ - PCB board, $4$ - NAND memory module, $5$ - crystal oscillator, $6$ - LED indicator , $7$ - write protection switch, $8$ - space for an additional memory chip.

Application

Exists There are two main uses for flash memory:

• as a mobile information carrier;
• as a repository for digital device software.

Often both methods are combined in one device.

The use of NOR memory, which has a relatively small volume, is to provide fast access to random addresses and guarantee the absence of bad elements (standard ROM chips for working with a microprocessor, computer boot chips (POST and BIOS), medium-sized data storage chips, for example , DataFlash). Typical volumes range from $100$ Kb to $256$ Mb. NAND memory is used in mobile devices and storage media that require the use of large amounts of storage. Basically, these are USB key fobs and memory cards of all types, as well as mobile devices (phones, cameras, players). NAND memory is built into household appliances: cell phones and TVs, network routers, access points, game consoles, photo frames and navigators.

Figure 4. Flash cards of different types

Types and types of memory cards and flash drives

Remark 1

CF(Compact Flash) is the oldest standard for memory types. It has high reliability, rather large volume ($128$ Gb and more) and high data transfer rate ($120$ Mb/s). Due to its large size, it is used in professional video and photo equipment.

MMC (Multimedia Card) is small in size, highly compatible with various devices, and contains a memory controller. SD Card (Secure Digital Card) is the result of the development of the MMC standard. The card has cryptoprotection against unauthorized copying, increased protection of information from accidental erasure or destruction, and a mechanical write protection switch. Maximum capacity up to $4$ GB. SDHC (SD High Capacity) has a maximum capacity of $32$ GB.

There are also miniSD and microSD cards.

Remark 2

The main manufacturers of NAND flash memory are Micron/Intel, SK Hynix, Toshiba/SanDisk, Samsung. The main manufacturers of NAND flash memory controllers are Marvell, LSI-SandForce and NAND memory manufacturers.

Flash memory is a type of durable memory for computers that can be reprogrammed or electrically erased. Compared to Electrically Erasable Programmable Read Only Memory, actions can be performed on it in blocks that are in different places. Flash memory costs much less than EEPROM, which is why it has become the dominant technology. Especially in situations where stable and long-term data storage is required. Its use is allowed in a wide variety of cases: in digital audio players, photo and video cameras, mobile phones and smartphones, where there are special android applications on a memory card. In addition, it is also used in USB flash drives, traditionally used to save information and transfer it between computers. It has gained some notoriety in the gamer world, where it is often used in a blunder to store game progress data.

general description

Flash memory is a type that can store information on its board for a long time without using power. In addition, we can note the highest data access speed, as well as the best resistance to kinetic shock in comparison with hard drives. It is thanks to these characteristics that it has become so popular for devices powered by batteries and accumulators. Another indisputable advantage is that when flash memory is compressed into a solid card, it is almost impossible to destroy it by any standard physical means, so it can withstand boiling water and high pressure.

Low-level data access

The method of accessing data in flash memory is very different from that used for conventional views. Low-level access is provided through the driver. Conventional RAM immediately responds to calls to read and write information, returning the results of such operations, but the design of flash memory is such that it takes time to think.

Device and principle of operation

At the moment, flash memory is widespread, which is created on single-transistor elements with a "floating" gate. This allows for greater storage density than DRAM, which requires a pair of transistors and a capacitor element. At the moment, the market is replete with various technologies for building basic elements for this type of media, which are developed by leading manufacturers. What distinguishes them is the number of layers, methods of recording and erasing information, as well as the organization of the structure, which is usually indicated in the name.

At the moment, there are a couple of types of microcircuits that are most common: NOR and NAND. In both, the storage transistors are connected to the bit buses - in parallel and in series, respectively. The first type has rather large cell sizes, and there is a possibility for fast random access, which allows programs to be executed directly from memory. The second is characterized by smaller cell sizes, as well as fast sequential access, which is much more convenient when it is necessary to build block-type devices where large information will be stored.

In most portable devices, the SSD uses the NOR type of memory. However, now USB devices are becoming more and more popular. They use NAND memory. Gradually, it displaces the first.

The main problem is the fragility

The first samples of mass-produced flash drives did not please users with high speeds. However, now the speed of writing and reading information is at such a level that you can watch a full-length movie or run an operating system on your computer. A number of manufacturers have already demonstrated machines where the hard drive is replaced by flash memory. But this technology has a very significant drawback, which becomes an obstacle to replacing existing magnetic disks with this carrier. Due to the nature of the flash memory device, it allows erasing and writing information for a limited number of cycles, which is achievable even for small and portable devices, not to mention how often this is done on computers. If you use this type of media as a solid state drive on a PC, then a critical situation will come very quickly.

This is due to the fact that such a drive is built on the property of field-effect transistors to store in a “floating” gate, the absence or presence of which in the transistor is considered as a logical one or zero in the binary. Recording and erasing data in NAND memory are performed using tunneled electrons using the Fowler-Nordheim method. with the help of a dielectric. This is not required, which allows you to make cells of minimal size. But it is this process that leads to the cells, since the electric current in this case causes the electrons to penetrate the gate, overcoming the dielectric barrier. However, the guaranteed shelf life of such memory is ten years. The wear of the microcircuit occurs not due to reading information, but due to operations to erase and write it, since reading does not require changing the structure of the cells, but only passes an electric current.

Naturally, memory manufacturers are actively working towards increasing the service life of this type of solid-state drives: they are striving to ensure uniform write / erase processes across array cells so that some do not wear out more than others. Software paths are predominantly used to evenly distribute the load. For example, to eliminate this phenomenon, the technology of "wear leveling" is used. In this case, data that is often subject to changes is moved to the address space of the flash memory, so the recording is carried out at different physical addresses. Each controller is equipped with its own alignment algorithm, so it is very difficult to compare the effectiveness of certain models, since implementation details are not disclosed. Since the volume of flash drives is growing every year, it is necessary to apply more and more efficient operation algorithms to guarantee the stability of the devices.

Troubleshooting

One of the very effective ways to combat this phenomenon was the reservation of a certain amount of memory, which ensures load uniformity and error correction through special logical redirection algorithms for replacing physical blocks that occur during intensive work with a flash drive. And to prevent the loss of information, cells that are out of order are blocked or replaced with backup ones. Such a software distribution of blocks makes it possible to ensure load uniformity by increasing the number of cycles by 3-5 times, but this is not enough.

And other types of such drives are characterized by the fact that a table with the file system is entered into their service area. It prevents failures in reading information at the logical level, for example, in the event of an incorrect shutdown or a sudden interruption in the supply of electrical energy. And since the system does not provide for caching when using removable devices, frequent overwriting has the most detrimental effect on the file allocation table and directory contents. And even special programs for memory cards are not able to help in this situation. For example, with a single access, the user rewrote a thousand files. And, it would seem, only once used for recording the blocks where they are located. But the service areas were overwritten with each update of any file, that is, the allocation tables went through this procedure a thousand times. For this reason, the blocks occupied by this particular data will fail first of all. Wear leveling technology works with such blocks, but its effectiveness is very limited. And it doesn’t matter what computer you use, the flash drive will fail exactly when it is provided by the creator.

It is worth noting that the increase in the capacity of the microcircuits of such devices only led to the fact that the total number of write cycles was reduced, as the cells become smaller, so less and less voltage is required to dissipate the oxide partitions that isolate the “floating gate”. And here the situation is such that with an increase in the capacity of the devices used, the problem of their reliability has become more and more aggravated, and the class of the memory card now depends on many factors. The reliability of such a solution is determined by its technical features, as well as the current market situation. Due to fierce competition, manufacturers are forced to reduce the cost of production in any way. Including due to the simplification of the design, the use of components from a cheaper set, the weakening of control over manufacturing, and in other ways. For example, a Samsung memory card will cost more than lesser-known analogues, but its reliability raises much fewer questions. But even here it is difficult to talk about the complete absence of problems, and it is difficult to expect anything more from devices from completely unknown manufacturers.

Development prospects

Despite the obvious advantages, there are a number of disadvantages that characterize the SD-memory card, preventing further expansion of its scope. That is why there is a constant search for alternative solutions in this area. Of course, first of all, they try to improve the existing types of flash memory, which will not lead to any fundamental changes in the existing production process. Therefore, there is no doubt about only one thing: the companies involved in the manufacture of these types of drives will try to use their full potential before switching to another type, continuing to improve traditional technology. For example, the Sony memory card is currently available in a wide range of sizes, so it is expected that it will continue to be actively sold.

However, today a whole range of alternative data storage technologies is on the verge of industrial implementation, some of which can be implemented immediately upon the onset of a favorable market situation.

Ferroelectric RAM (FRAM)

Ferroelectric RAM (FRAM) technology is proposed to increase the potential of non-volatile memory. It is generally accepted that the mechanism of operation of existing technologies, which consists in rewriting data in the process of reading with all modifications of the basic components, leads to a certain restraint in the speed potential of devices. And FRAM is a memory characterized by simplicity, high reliability and speed of operation. These properties are now characteristic of DRAM - the non-volatile random access memory that exists at the moment. But this will also add the possibility of long-term data storage, which is characterized. Among the advantages of this technology, resistance to various types of penetrating radiation can be distinguished, which may be in demand in special devices that are used to work in conditions of increased radioactivity or in space exploration. The information storage mechanism is implemented here through the use of the ferroelectric effect. It implies that the material is able to maintain polarization in the absence of an external electric field. Each FRAM memory cell is formed by placing an ultra-thin film of ferroelectric material in the form of crystals between a pair of flat metal electrodes that form a capacitor. The data in this case is stored inside the crystal structure. And this prevents the effect of charge leakage, which causes the loss of information. The data in the FRAM memory is retained even when the power supply is switched off.

Magnetic RAM (MRAM)

Another type of memory that is considered very promising today is MRAM. It is characterized by rather high speed performance and energy independence. in this case, a thin magnetic film placed on a silicon substrate is used. MRAM is a static memory. It does not need to be periodically overwritten, and the information will not be lost when the power is turned off. At the moment, most experts agree that this type of memory can be called the next generation technology, since the existing prototype demonstrates fairly high speed performance. Another advantage of this solution is the low cost of the chips. Flash memory is manufactured according to a specialized CMOS process. And MRAM chips can be produced using a standard manufacturing process. And the materials can be those that are used in conventional magnetic media. It is much cheaper to produce large batches of such microcircuits than all the others. An important property of MRAM memory is the ability to turn on instantly. And this is especially valuable for mobile devices. Indeed, in this type, the value of the cell is determined by the magnetic charge, and not by the electric charge, as in traditional flash memory.

Ovonic Unified Memory (OUM)

Another type of memory that many companies are actively working on is the solid-state drive based on amorphous semiconductors. It is based on the phase transition technology, which is similar to the principle of recording on conventional discs. Here the phase state of matter in an electric field changes from crystalline to amorphous. And this change persists even in the absence of tension. Such devices differ from traditional optical discs in that the heating occurs due to the action of an electric current, and not a laser. Reading in this case is carried out due to the difference in the reflectivity of the substance in different states, which is perceived by the drive sensor. Theoretically, such a solution has a high storage density and maximum reliability, as well as increased speed. The indicator of the maximum number of rewriting cycles is high here, for which a computer is used, the flash drive in this case lags behind by several orders of magnitude.

Chalcogenide RAM (CRAM) and Phase Change Memory (PRAM)

This technology is also based on the basis when in one phase the substance used in the carrier acts as a non-conductive amorphous material, and in the second it serves as a crystalline conductor. The transition of the storage cell from one state to another is carried out due to electric fields and heating. Such chips are characterized by resistance to ionizing radiation.

Information-Multilayered Imprinted Card (Info-MICA)

The operation of devices built on the basis of this technology is carried out according to the principle of thin-film holography. Information is recorded as follows: first, a two-dimensional image is formed, which is transferred to a hologram using CGH technology. Data is read by fixing the laser beam on the edge of one of the layers being recorded, which serve as optical waveguides. Light propagates along an axis that is parallel to the plane of the layer, forming an output image corresponding to the information recorded earlier. The initial data can be obtained at any time thanks to the reverse coding algorithm.

This type of memory compares favorably with semiconductor memory due to the fact that it provides high recording density, low power consumption, as well as low media cost, environmental safety and protection from unauthorized use. But such a memory card does not allow information to be rewritten, therefore it can only serve as a long-term storage, a replacement for paper media, or an alternative to optical discs for distributing multimedia content.

A new word has appeared in everyday life of users - “flash drive”. Most people know for sure that this device is used in digital cameras, and is also designed to transfer movies and music. But this is not a complete list of functions that a flash drive performs. This device is indispensable in the work of any owner of not only a computer, but also all kinds of electronics of the 21st century. The topic of this article is flash memory, its characteristics, types, prices.

Immersed in history

All the giants of the IT industry are rewriting history, establishing their authorship over various inventions. So did the famous American company Intel, which appropriated the invention of flash memory. However, the technology and production of the world's first device belongs to the Japanese giant Toshiba, who presented his discovery to the world back in 1984. The name "flash memory" was also given to the device by the Japanese, and not by chance. The process of erasing information on flash memory is vaguely reminiscent of a flash.

Not even a few years have passed since the invention, and the global giants of the IT industry quickly found a use for the new invention, putting production on the conveyor.

Not all memory is "flash"

A shallow dive into the world of physics reveals that there are several types of memory.

1. RAM, which works on the principle of "electric capacitance". Millions of capacitors, holding the charge in the RAM, are the custodians of information. When the power supply to the device is turned off, the capacitors are discharged, losing information irretrievably.
2. Permanent memory. Information on the carrier is stored by physical or chemical influence. An example is an optical DVD disc, on which information is recorded by burning microscopic holes on the plastic surface with a laser.
3. Conditionally-permanent non-volatile memory. This includes flash memory, magnetic hard drives, floppy disks, videotape, and other media that can hold a magnetic or electrical charge in the absence of a permanent power source.

Flash memory application

For the technologies of the 20th century, the invention was quite sufficient for devices such as a memory card and USB flash drives. But in the 21st century there was a boom in storage media with flash technology. First of all, all mobile phones, tablets, multimedia players and digital devices acquired flash memory. Later, no interactive toy for children could exist without flash memory. Technology didn't stop there. Every day there are new devices equipped with such a wonderful kind of memory. Take at least a flashlight for the policeman. Due to the presence of flash memory in it, a human rights activist can choose the focus and brightness of the beam he needs from the saved settings.

How many device manufacturers

On the market, you can see that the required flash memory is represented by several manufacturers at once. Having almost the same characteristics, the drives differ significantly in price. Is the most expensive purchase going to be the best? Not always! Often the buyer has to overpay for the brand, service and warranty.

There are only a few factories in the world that produce flash memory modules. These modules are snapped up by the giants of the IT industry, who create a beautiful case and sell the drive in their own name. The only difference is the speed of the devices, which depends on the capabilities of the flash memory. Whether the memory is fast or not is decided at the factory.

About prices for flash devices

For anyone who decides to purchase flash memory on their own, the prices on the market may seem strange. Drives of the same volume from two unfamiliar brands have a large difference in cost. What's the matter? There is a set of requirements for flash cards, due to which the manufacturer is obliged to determine the class of the device and mark it on the product case. Often in the store you can find devices on which there is no marking, there is only the logo of the manufacturer. The prices for such memory cards are very low, and the seller claims high performance of the device. Reviews of experts on the pages of respected computer publications recommend refraining from buying unmarked devices, as they are fake or imported into the country illegally.

What you need to know about flash drive labels

Since we are talking about the labeling of drives, when buying, you need to pay attention to the numbers and inscriptions indicated on the case of flash devices.

1. The name of the manufacturer or its logo must be present.
2. The amount of flash memory must be written on the media.
3. The class of the flash device must be indicated on the case. Often manufacturers of USB modules indicate the class on the product packaging, which is not prohibited by law.

On sale you can find flash memory cards without marking, but with a long number, which is printed in small print on the device case. Thus, the manufacturer indicates the batch number by which the buyer can find the device on the Internet and get acquainted with its technical characteristics.

Speed ​​is proportional to price, but not efficiency

The higher the class of flash memory, the higher its write speed, and the higher the price. Is it worth buying the fastest memory?

1. Zero class. Write speed of at least 0.6 Mb per second. You can buy it in stores without seeing the absence of markings. Good for document storage.
2. Classes 2 and 4, with write speeds of 2 and 4 MB per second, respectively, also belong to the office section and are designed for storing and transferring documentation.
3. The sixth and eighth grades with a speed of 6 and 8 Mb per second will be of interest to all buyers working with photos, music, videos. These types of flash memory unlock the potential for multimedia.
4. Class ten and above, including Ultra, show write speeds over 10 MB per second. They are used in working with multimedia, as additional drives for workstations, and used as RAM. Where the speed of reading and writing to the storage medium is critical.

Major brands such as Pretec and Corsair make high-speed devices that can write about 25MB per second, labeling them eighth or tenth grade. The price of modules is very high, but in the IT world, such brands are highly respected by users.

What are the different sizes of flash memory

Another criterion on which the price of a drive depends is the amount of flash memory. Although technology does not stand still, there are still some limits. When it is necessary to change the manufacturing process to increase the amount of memory, a dilemma arises - while maintaining a low price, stop at the achieved result or develop further, looking for wealthy buyers. There has been some lull in the world - customers are offered to buy memory cards with a maximum capacity of 64 gigabytes, with a strong desire, you can become the owner of 128 GB and 256 GB on order, but for this you will have to fork out a lot. It is not known how long it will take for the transition to new technologies and the availability of large-capacity cards on the market, but one thing is known - 64 GB is enough to satisfy any task of an ordinary user.

Wonder beast with a great future

There is another interesting device that uses flash memory in its work - an SSD drive. Along with the volume and speed of recording, the credibility of the manufacturer is critical for the device, which provides the product with a control controller and specialized firmware that controls the entire device. One manufacturer's mistake - and the device can end up in the trash. Everything is complicated, expensive and very serious, but the future belongs to the SSD drive. A direct competitor to computer hard drives that work using magnetism. Resistant to shaking, temperature and silent operation. The day is not far off when magnetic hard drives will share space in the closet with ball mice, giving way to 21st century technology.

How to save money on computer upgrades

Owners of old computers and laptops have often heard from service specialists about the reasons for the low speed of the device. There is not enough RAM, which has long been discontinued. The specialist, looking into the eyes of the owner of the computer, convinces that the only way out of the situation is to buy a modern computer. After 5 years, the same specialist will come and prove once again that there are no solutions other than buying a new computer. This is how the world is built. A world for people who are not interested in knowledge in IT technologies.

RAM flash memory will solve the problem once and for all with minimal cost to the user. It is enough to download a program called Ready Boost from the Internet and study the system requirements for the drive. And only then purchase the necessary flash memory device in the store. Connect a drive to a computer or laptop, run the program and enjoy life. It's so nice to independently increase the performance of your computer without capital investments.

Which brand to prefer

Due to the large number of manufacturers, it is very difficult to decide who to give preference to. Experts recommend making a list of requirements for the drive, and then choosing a brand.

1. The purpose of use allows you to identify the required class of device.
2. Convenience and appearance will tell you how the flash drive should look. For example, for a radio tape recorder in a car, you should pay attention to a small drive so as not to accidentally break it during use.

Having found several required options, ask the seller how issues are resolved when the device breaks down, whether there is a warranty replacement. Flash memory is a consumable and cannot be repaired - you need to know about this before buying. Manufacturers Corsair, Kingston, OCZ, Pretec, Silicon Power, Transcend and IBM deserve positive feedback.

How to protect yourself from losing information from a flash drive

Like any storage medium, a memory card is subject to external factors that all users of flash devices need to be aware of and take care of the safety of their information.

1. Physical failure of modules. Plastic flash cards are very easy to break, but impossible to restore, so when buying, you need to pay attention to metal flash drives or use them very carefully.
2. Moisture can destroy the drive. It is worth paying attention to waterproof media if there is a possibility of water getting on the memory.
3. Infection of flash memory with viruses. Sometimes it is quite difficult to recover information, so you should pay attention to devices that have physical write protection in the form of a switch - this is guaranteed not to give viruses a single chance.

Having found out the principle of operation, types, characteristics, prices and flash memory device, you need to entrust your choice to professionals.

1. Experts recommend giving preference to trusted brands. To do this, just turn to popular sources of information and read reviews about the product. Any self-respecting manufacturer on the Internet has its own website. Here it is worth visiting to get an idea about the company.
2. Do not trust your choice of Chinese fakes, which are offered on the market at a very low price. If there are no other options, be sure to ask the seller to demonstrate the operation of the media before buying. The usual formatting of the device in the Windows environment allows you to determine the health of the flash memory.
3. Preference should be given to fast devices that have the tenth class. Since there are often situations when time is a priority. Then the flash memory will become universal for the user for any device.
4. When buying memory cards for digital technology, you should worry about the ability to read data on a computer. To do this, there are all kinds of adapters that are often offered for purchase along with flash memory.

Modern technologies are developing quite quickly, and what yesterday seemed to be the height of perfection, today does not suit us at all. This is especially true for modern types of computer memory. Memory is constantly lacking or the media speed is very low, by modern standards.

Flash memory appeared relatively recently, but having many advantages, it seriously crowds out other types of memory.

Flash memory is a type of solid-state, non-volatile, rewritable memory. Unlike a hard disk, a flash drive has a high read speed, which can reach up to 100 Mb / s, a very small size. It can be easily transported as it connects via a USB port.

It can be used as RAM, but unlike RAM, flash memory stores data when the power is off, autonomously.

Today, flash drives are available on the market with a volume of 256 megabytes to 16 gigabytes. But there are carriers with a large volume.

Additional flash memory features include copy protection, a fingerprint scanner, an encryption module, and much more. Also, if the motherboard supports booting via a USB port, then it can be used as a boot device.

The new flash technologies include UЗ. This media is recognized by the computer as two disks, where data is stored on one, and the computer boots from the second. The advantages of this technology are obvious, you can work on any computer.

The rather small size allows the use of this type of memory very widely. This includes mobile phones, cameras, video cameras, voice recorders and other equipment.

In the description of the technical characteristics of any mobile device, the type of flash memory is indicated, and not by chance, since not all types are compatible. Based on this, you need to choose flash drives that are quite common on the market so as not to have problems with any device.
For some types of flash cards, there are adapters that expand its capabilities.

Existing types of flash memory

Modern flash cards can be divided into six main types.

The first and most common type is Compact Flash (CF), there are two types CF type I and CF type II. It has good speed, capacity and price.
The disadvantages include the size of 42 * 36 * 4 mm. It is quite versatile and is used in many devices.

IBM Microdrive-cheap, but less reliable and consumes more than usual energy, which is the reason for its limitation.

smart media- thin and cheap, but not high abrasion protection.

Multimedia Card (MMC)- small size (24x32x1.4mm), low power consumption, used in miniature devices. The disadvantage is low speed.

SecureDigital (SD) with comparable dimensions with Multimedia Card, it has a larger volume and speed. But more expensive.

memory stick- has good information protection, speed, but not very large capacity.

Today, CompactFlash and SD / MMC are considered the most common, but
in addition to the listed cards, there are other types of flash cards

It is worth choosing a flash card based on your needs, given that the larger the volume and speed, the more expensive the flash card.

Despite the progress of computer technology, only 3-4 years ago, many new computers (and even older ones) had a floppy drive in their composition. A significant reduction in the cost of optical drives and CDs could not replace 3.5-inch floppy disks. It is inconvenient to use optical media and that's it. If reading data from them still does not cause much discomfort, then writing and deleting already required some time. Yes, and the reliability of disks, although many times higher than that of floppy disks, still after some time, especially after active use, it begins to fall. As always, at the most inopportune moment, the drive from old age (its own or the disk) will “buck up” and say that the disk is not noticeable on the horizon.

So floppy disks lasted so long. It is still quite possible to carry on them some trifle like documents, or source codes of programs. But now even for this type of data sometimes there is not enough 1.38 MB of free space.

The solution to the problem has been around for a long time. Its name is flash memory. It was invented back in the 80s of the last century, but it got to really mass products by the end of the 90s. And moreover, at first it was available to us as a memory card, and then in the form of MP3 players, which today have already changed the MP3 abbreviation to a more proud and generalizing epithet "digital".

This was followed by the advent of USB-flash drives. The process of their penetration was at first not the fastest. It began with the advent of solutions for 16-64 MB. Now this is a minuscule, but 8 years ago, compared to a floppy disk, it was hoo as good. And plus to this was added ease of use, high read / write speed and, of course, a high price. Then such flash drives were more expensive than a writing optical drive, which themselves were estimated at about $100.

However, the convenience of flash drives has had a decisive influence on consumer choice. As a result, in 2005 a real boom began. The cost of flash memory has fallen many times over, and with it the storage capacity has grown. As a result, today for some 2000-2500 rubles you can buy a 32 GB flash drive, while a year ago this cost almost twice as much.

The progress in the field of flash memory has been so successful that it is now beginning to compete with hard drives. So far, only in the field of read / write speed and access time, as well as in energy indicators and durability, but a victory in capacity in the coming years cannot be ruled out either. The only advantage of HDD is the price. One "hard" gigabyte costs much less. But this is only a matter of time.

So, flash memory is one of the most promising computer technologies for data storage. But where did it come from and what are its possible limitations and disadvantages? It is these questions that this article aims to answer.

Past

While Japanese movers were unloading one of the first batches of Apple computers brought in refrigerators because of the picture of an apple on the boxes, a Japanese scientist named Fujio Masuoki was working within the walls of Toshiba's research laboratory on a new type of memory. The name was not invented immediately, but the prospects for the invention were visible to the scientist from the very beginning.

However, the name was decided rather quickly. Fujio's colleague, Mr. Shoji Ariizumi, suggested calling the new memory "flash". One of the translations of this word means a camera flash (and, in principle, any other flash of light). That was the idea that Shoji had come up with with the method of erasing data.

The new technology was presented in 1984 in San Francisco at an event called the International Electron Devices Meeting (international meeting of manufacturers of electronic devices), held by the IEEE Institute. They noticed it right away, and quite large companies. For example, Intel released its first commercial NOR chip as early as 1988.

Five years later, in 1989, Toshiba introduced NAND flash memory technology at a similar event. Today, this type is used in the vast majority of devices. Why exactly - we will tell in the next section.

NOR and NAND

NOR memory was introduced a little earlier because it is a little easier to manufacture, and its transistors in their structure resemble a conventional MOSFET transistor (channel field unipolar MOSFET). The only difference is that in NOR-memory, the transistor has a second, "floating" gate in addition to the control gate. The latter, with the help of a special insulating layer, can retain electrons for many years, keeping the transistor not discharged.

In general, NOR memory got its name because of its work as a NOR gate (NOR is a logical NOR operation; it takes the value "true" only when both inputs are "false"). So the empty NOR memory location is filled with the boolean value "1". By the way, the same applies to NAND-memory. And, as you might guess, it got its name because of the similar principle of working with a NAND gate (NAND is a logical NAND operation; it takes the value "false" only when "true" is applied to both inputs).

What results in practice these very "NOT-AND" and "NOT-OR"? The fact that the NOR-memory chip can only be cleared entirely. Although in more modern incarnations of this technology, the chip is divided into several blocks, usually occupying 64, 128 or 256 KB. But this type of memory has an external address bus, which allows byte-by-byte reading and programming (writing). This allows not only accessing data directly as accurately as possible, but also executing them directly "on the spot", without unloading all the information into RAM. This feature is called XIP (eXecute In Place).

It is also worth talking about a relatively new NOR memory feature called BBM (Bad Block Management - bad block management). Over time, some of the cells may become unusable (more precisely, their recording will become unavailable) and the chip controller, noticing this, will reassign the address of such cells to another, still working block. Hard drives are also doing something similar, as we wrote about in the article "".

Thus, NOR-memory is well suited for cases where maximum data reading accuracy and rather rare data changes are required. Guess what we're getting at? That's right - to the firmware of various devices, in particular the BIOS of motherboards, video cards, etc. It is there that now NOR-flash is used most often.

As for NAND, the situation with it is a little more "tricky". Data can be read only page by page, while writing can be done block by block. One block consists of several pages, and one page is usually 512, 2048 or 4096 bytes in size. The number of pages in a block, as a rule, varies from 32 to 128. So there is no question of any execution "on the spot". Another limitation of NAND memory is that a block can only be written to sequentially.

As a result, such accuracy (although it would be more correct to say "not accuracy") sometimes leads to errors, especially if you have to deal with MLC memory (more on this type below). To correct them, the ECC mechanism is used. It can fix 1 to 22 bits in every 2048 bits of data. If correction is not possible, the engine determines that there is an error while writing or erasing data and the block is marked as "bad".

By the way, to prevent the formation of bad blocks in flash memory, there is a special method called "wear leveling" (literally, "wear level"). It works quite simply. Since the "survivability" of a flash memory block depends on the number of erase and write operations, and this number is different for different blocks, the device controller counts the number of these operations for blocks, trying to write to those that were used less over time. That is, those that are less "worn out".

Well, as for the scope of NAND-memory, due to the possibility of denser placement of transistors, and at the same time their cheaper manufacture, it is just used in all flash memory cards and USB flash drives, as well as SSD.

Well, a little about SLC (Single-Level Cell - single-level cell) and MLC (Multi-Level Cell - multi-level cell) cells. Initially, only the first type was available. It assumes that only two states, that is, one bit of data, can be stored in one cell. MLC chips were invented later. Their capabilities are slightly wider - depending on the voltage, the controller can read more than two values ​​​​from them (usually four), which allows you to store 2 or more bits in one cell.

Advantages of MLC on the face - with the same physical size, twice as much data is placed in one cell. The disadvantages, however, are no less significant. First of all, this is the reading speed - it is naturally lower than that of the SLC. After all, it is required to create a more accurate voltage, and after that it is necessary to correctly decipher the information received. And then there is a second drawback - the inevitable errors in reading and writing data. No, the data is not damaged, but this affects the speed of work.

A rather significant disadvantage of flash memory is the limited number of data write and erase cycles. In this regard, it still can not compete very well with hard drives, but in general the situation is improving every year. Here is the service time data for different types of flash memory:

• SLC NAND - up to 100 thousand cycles;
• MLC NAND - up to 10 thousand cycles;
• SLC NOR - from 100 to 1000 thousand cycles;
• MLC NOR - up to 100 thousand cycles.

Here is another disadvantage of MLC memory - it is less durable. Well, NOR-flash is generally out of competition. True, this is of little use to the average layman - anyway, his flash drive is most likely built on the basis of a NAND flash, and even on MLC chips. However, technology does not stand still, and NAND-flash with a million cycles of writing and erasing data is gradually coming to the masses. So over time, these parameters will become of little importance to us.

"Cards"

Having dealt with the types of flash memory, now let's move on to real products based on it. Of course, we will omit the description of BIOS chips, since most readers are of little interest in them. Just as it makes no sense to talk about USB flash drives. With them, everything is extremely simple: they are connected via a USB interface, the chips installed inside are entirely dependent on the manufacturer. There are no standards for these media, except for the need for USB compatibility.

But standards are required for flash cards, which are now used in digital cameras, players, mobile phones and other mobile devices. A card reader for them is available in most laptops and netbooks, and one can also be found in household DVD (or Blu-ray) players or car radios.

For these devices, there is one universal characteristic - the number of supported memory cards. Sometimes on card readers you can see the proud inscriptions "20-in-1" or even "30-in-1", meaning the number of supported formats. But what is most surprising, there are only 6 fundamentally different mass formats. All the rest are their modifications. Here on these six standards we will stop further.

compact flash

The CompactFlash format occupies a special place among all other formats of flash memory cards. First of all, because it was the very first mass standard. It was introduced by SanDisk in 1994. And until now, it is actively used in digital SLR cameras, as well as router computers and other highly specialized devices.

The most interesting thing is that the first CF cards were based on NOR chips manufactured by Intel. But then they were quickly transferred to NAND-flash, which made it possible to reduce the cost and increase the capacity.

CompactFlash was created as a format for external data storage. But since there were no card readers 15 years ago, and USB was just being designed, CF cards were created based on the ATA (IDE) interface specifications. Thus, such a card can be connected to a regular IDE connector or inserted into a PC Card slot via a passive adapter. That is why CompactFlash is very convenient to use in routers and similar devices - speed and large volume are not required there, but dimensions, shock resistance and low heat are much more relevant.

In addition, it is not difficult to make an adapter for the USB or FireWire interface. And, most interestingly, most card readers use the CompactFlash I / O system to exchange data between a computer and other formats: SD / MMC, Memoty Stick, xD and SmartMedia.

Now about various modifications of the CompactFlash standard. Initially, such cards were issued in a single "cartridge" sized 43x36x3.3 mm. It still applies today. But when the one-inch IBM Microdrive hard drive was introduced, a second form factor was added with dimensions of 43x36x5.0 mm. Thus, the first became known as CF Type I, and the second - CF Type II. After the release of Microdrive (and its analogues) was stopped, the relevance of the CF Type II came to naught.

CompactFlash has a few more revisions. Their need arose as read / write speeds increased, as well as volume. So revision 2.0 increased the maximum speed to 16 MB / s. Later, revision 3.0 appeared, increasing this value to 66 MB / s. Well, the latest version 4.0 / 4.1 allows you to exchange data at speeds up to 133 MB / s. The last value corresponds to the UDMA133 standard, which is also already losing its relevance.

To replace the fourth revision is already being prepared... no, not a new revision - a new format - CFast. Its main fundamental difference is the use of the SerialATA interface instead of IDE. Of course, this completely blocks backward compatibility with the previous type of connector, but increases the maximum speed to 300 MB / s and the possibility of increasing the volume to much more than 137 GB. Note that CFast uses seven pins for data exchange, just like a regular SATA interface. But power is supplied through 17 pins, while SATA devices have 15 of them. So you won't be able to directly connect the CFast card to the motherboard, you will have to use an adapter. Such cards should appear already this year. In January, at CES 2009, the first samples with a capacity of 32 GB were already demonstrated.

Now it remains to talk about the speed of data exchange and the volumes of CompactFlash cards available today. The speed of CF cards (and other flash memory drives, except for SSDs, too) is measured exactly the same as that of CDs. That is, 1x corresponds to 150 KB / s. On the fastest representatives, there are inscriptions 300x, which corresponds to 45 MB / s. In principle, it’s not a little, but it’s far from hard drives paired with SSDs. But over time, the speed will only increase.

Well, as for the volume, CompactFlash cards with a capacity of 2 MB to 100 GB have been released for all the time. Today, the most common options are from 1 to 32 GB. However, 48, 64 and 100 GB versions are already available for sale, although they are still quite rare. So far, the CompactFlash format offers the most capacious flash memory cards. But others may offer other benefits. We read about them further.

smart media

SmartMedia became the second mass flash card format. It was introduced a year later than CompactFlash - in the summer of 1995. Actually, it was created as a competitor to CF. What did SmartMedia have to offer? First of all, smaller sizes. And to be even more precise, then only a smaller thickness - only 0.76 mm; the width and length of such cards was 45x37 mm, while for CompactFlash these parameters are almost the same - 43x36 mm. It should be noted that in terms of thickness, SM has not yet surpassed any other format. Even ultra-compact microSD cards are "fatter" - 1 mm.

A similar indicator was achieved thanks to the removal of the controller chip. It has been moved to the card reader. Yes, and inside the SM-card itself, at first, one NAND-chip could be placed, but then, as the technology improved, there were more of them.

But the lack of a controller inside the card has certain disadvantages. Firstly, as the volume grew and new media models were released, it was necessary to update the firmware of the card reader. And this operation was not always available if the card reader was very old. Also, over time, confusion began with the operating voltage of SmartMedia cards. Initially, it was 5.0 V, and then 3.3 V. And if the card reader did not support one of them, then it could not work with such cards. Moreover, inserting a 3.3V card into a 5.0V card reader could damage or burn it.

Secondly, for the SmartMedia format, it is impossible to use the method of calculating the wear level of flash memory blocks (we described the wear leveling method in the previous section). And this potentially threatens to shorten the life of the memory card.

However, all this did not prevent SmartMedia from being used as the main format for digital cameras for quite a long time - in 2001 it was supported by up to half of such devices on the market, although then this market was much more modest than today. In other digital devices such as players, PDAs or mobile phones, SmartMedia has not found itself. Yes, and camera manufacturers began to abandon SM. The cameras were getting smaller and the small thickness of these cards was no longer enough. Well, the second significant minus is the increase in the need for more capacity. SmartMedia cards have reached only 128 MB. 256 MB variants were planned, but they were never released.

In general, SmartMedia was conceived as a replacement for 3.5-inch floppy disks. They even released a special adapter called FlashPath. It was introduced in May 1998 and a year later they sold a million pieces. It was developed by SmartDisk, which, by the way, produced similar adapters for MemoryStick and SD/MMC cards.

The most amazing thing is that FlashPath can work with any floppy drive, excellent logo "HD" (High-Density - high density). In short, anyone who reads a 1.44 MB floppy is fine. But there is one "but". You can't do without it. And here there are two of them. First, a special driver is required to recognize the FlashPath adapter and the card inside it. And if it is not available for the desired OS, then it is in flight. So it will not work from such a floppy disk. The second "but" is the speed of work. It does not exceed that when working from a conventional floppy disk. And if 1.44 MB could be copied or written in a little more than a minute, then 64 MB would take more than an hour.

Today, the SmartMedia format can be called dead. Some card readers still support it (especially the most frivolous a la "all-in-1"), but this compatibility is simply not relevant. Although, of course, this standard has made a certain contribution to the development of flash technologies.

The MMC format was introduced third in 1997. It was developed by SanDisk and Siemens AG. The abbreviation MMC stands for MultiMediaCard, which immediately indicates the purpose of the standard - digital multimedia devices. This is where MMC is most often used.

In principle, MMC is very strongly associated with SD, especially their first versions. However, they diverged in their development and today the second one is the most common. So we will talk about it in the next subsection.

MMC unlike CompactFlash and SmartMedia has more compact dimensions. In terms of length and width: 24x32 mm. MMC cards are 1.4mm thick, which is about twice as thick as SM cards. But this parameter is not as critical as the other two measurements.

Over the entire existence of MMC, as many as eight different modifications of its cards have been presented. The first (simply MMC) uses a one-bit serial interface for data transmission, and its controller operates at a frequency of up to 20 MHz. This means a maximum speed of no more than 20 Mbps (2.5 Mbps or about 17x). In principle, it is quite modest by modern standards, but 12 years ago it was enough.

In 2004, the RS-MMC form factor was introduced. The prefix RS stands for Reduced-Size or "reduced size". Its dimensions are as follows: 24x18x1.4 mm. You can see that the height has almost doubled. Otherwise, it was exactly the same MMC memory card. But to install it in a card reader, you must use a mechanical adapter.

The DV-MMC format (DV stands for Dual-Voltage - double voltage) turned out to be rather short-lived. Such cards could work at a standard voltage of 3.3 V and at a reduced 1.8 V. This is necessary to save energy. There is clearly a focus on mobile devices. But DV-MMC cards were quickly phased out due to the advent of MMC+ (or MMCplus) and MMCmobile formats.

MMC+ and MMCmobile differed quite significantly from the original MMC specification and represented its fourth version. However, this did not prevent them from maintaining full backward compatibility with older card readers and devices, but a firmware update was required to use their new features. And these possibilities were as follows. 4- and 8-bit interfaces were added to the one-bit data exchange interface. The controller frequency could be from 26 to 52 MHz. All this raised the maximum speed to 416 Mbps (52 Mbps). Both of these formats supported operation with a voltage of 1.8 or 3.3 V. They did not differ in size from MMC and RS-MMC, respectively MMCplus and MMCmobile.

Later, the smallest MMC appeared - MMCmicro. The dimensions of the card were 14x12x1.1 mm. This format was based on MMC+ with some limitations. In particular, due to the lack of additional contacts (MMC has 7, MMC + has 13), the data exchange interface did not support 8-bit data transfer.

There is also such an unusual format as miCard. It was introduced in the summer of 2007 with the aim of creating a universal card that can be inserted into both an SD / MMC card reader and a USB connector. The first cards were supposed to have a capacity of 8 GB. The maximum reaches 2048 GB.

Well, the last one is SecureMMC. It is also based on the version 4.x specification used by MMC+. Its main feature is DRM protection support. By the way, this is what originally differed from the SD format MMC. SecureMMC is an attempt to compete with SD. So let's move on to this standard.

The SD (Secure Digital) format is by far the most popular. It and its modifications are used everywhere: in digital players and cameras (even reflex cameras), in PDAs and mobile phones. Probably the reason for this lies in its constant support and development from many companies.

SD was introduced in 1999 by Matsushita and Toshiba. A full-size Secure Digital card is the same size as an MMC card - 32x24x2.1 mm. The large thickness is due to the presence of a key blocking the entry. However, the SD specification allows you to make cards without it (they are called Thin SD), then the thickness drops to 1.4 mm.

Initially, the SD release was intended to compete with MemoryStick (described below), which supported DRM protection of media files. Then the development companies mistakenly assumed that the giants of the media industry would push online stores so hard that all files would be protected by DRM. So we decided to hustle.

Secure Digital is based on the MMC specifications. That is why SD card readers easily work with MMC. Why not vice versa? To protect the contacts from wear on SD cards, they were somewhat recessed into the case. Therefore, the contacts of the card reader, aimed only at working with MMC, simply will not reach the contacts of the SD card.

In terms of the variety of formats, SD is no less "modest" than its predecessor. First of all, it should be noted that two more form factors were presented: miniSD (20x21.5x1.4 mm) and microSD (11x15x1). The latter was originally created by SanDisk and was called T-Flash and then TransFlash. And then it was adapted as a standard by the SD Card Association.

The remaining differences relate to the capacity of the cards. And there is some confusion here. It began with the first generation of cards, which reached the volume of 2 GB. The SD card is identified by a 128-bit key. Of these, 12 bits are used to indicate the number of memory clusters and another 3 bits to indicate the number of blocks in the cluster (4, 8, 16, 32, 64, 128, 256 or 512 - a total of 8 values, which corresponds to three memory bits). Well, the standard block size for the first versions was 512 bytes. Total 4096x512x512 gives 1 GB of data. Sailed.

When the lack of capacity began to squeeze "from above", version 1.01 of the specification appeared, which allowed using an additional bit to additionally determine the size of the block - it could now be 1024 or 2048 bytes, and the maximum capacity increased to 2 and 4 GB, respectively. But bad luck - old devices could incorrectly determine the size of new memory cards.

In June 2006, a new edition of the standard appeared - SD 2.0. He was even given a new name - SDHC or Secure Digital High Capacity (Secure Digital High Capacity). The name speaks for itself. The main innovation of SDHC is the ability to create cards up to 2 TB (2048 GB). In principle, the minimum limit is not limited, but in practice SDHC cards have a capacity of 4 GB or more. It is noteworthy that the maximum limit is artificially limited - 32 GB. For more capacious cards, it is proposed to use the SDXC standard (more on that below), although several manufacturers have introduced 64 GB SDHC.

The SD 2.0 standard uses 22 bits of data to define the size, but four of these are reserved for future use. So card readers that are not originally adapted to work with SDHC will not be able to recognize new memory cards. But new devices easily recognize old cards.

Along with the announcement of the SDHC format, identification by speed classes appeared. There are three options: SD Class 2, 4 and 6. These numbers indicate the minimum data exchange rate for the card. That is, a card with SD Class 6 will provide a speed of at least 6 MB / s. Well, the upper limit is naturally not limited, although so far the situation with SD cards is approximately the same as with CompactFlash - the fastest representatives have reached a speed of 300x or 45 MB / s.

It is worth adding that miniature form factors have also undergone modernization. Nobody forgot about miniSDHC and microSDHC. However, mostly the first cards come across for sale. Today, their maximum volume has already reached 16 GB, and 32 GB options are on the way.

Well, the latest novelty is the standard. Whether it was called version 3.0 or not, we have not been able to find out. However, it differs from SDHC not so significantly. First of all, the artificial limit on the maximum volume was removed for it, which can now reach 2 TB. The maximum data exchange rate has been increased to 104 MB / s, and in the future they promise to raise it to 300 MB / s. Well, exFAT was chosen as the main file system (it is described below), while SDHC is content in most cases with FAT32. The first SDXC cards have already been announced and they have a capacity of 32 or 64 GB. But products with their support will still need to wait for some time.

Actually, everything about SD cards. But within the framework of this standard, several more interesting things were released. For example, the SDIO (Secure Digital Input Output) specification. According to it, using the form factor and interface of SD cards, you can create devices such as GPS receivers, Wi-Fi and Bluetooth controllers, modems, FM tuners, Ethernet adapters, etc. That is, the SD slot in this case serves as a kind of USB analog.

SanDisk distinguished itself with SD Plus cards, which immediately integrated a USB connector. Quite an interesting development is Eye-Fi. This is a memory card with a built-in Wi-Fi controller. The latter can transfer data from the card to any computer. Thus, there is no need to even remove it from the camera or phone.

In total, today the Secure Digital format is the most popular and fastest growing. So far, Sony is trying to resist him with its Memory Stick, but it turns out badly for her.

memory stick

Sony is known for its dislike of most formats and standards that were not developed by it. It is understandable - you will not receive royalties from them. So in the end, DVD + R / RW and Blu-ray and Memory Stick cards appeared. Introduced in October 1998, they are still distributed only among Sony products. Yes, and by and large only Sony and a little SanDisk are engaged in their release. The result of this is natural: a relatively low prevalence and a higher price than other flash cards of the same size.

Over the entire existence of the Memory Stick, Sony has released as many as seven modifications. Moreover, unlike MMC, they are all in use. As a result, natural confusion arises, and at the same time, card reader manufacturers can increase the number of recognized standards by their products.

It all started with just a Memory Stick. This is an elongated memory card measuring 50x21.5x2.8 mm. Its shape is somewhat reminiscent of a piece of chewing gum. It differed, as we wrote above, in DRM support, which was never required. The capacity varied from 4 to 128 MB.

Over time, this became insufficient, and since an updated standard had not yet been developed, the Memory Stick Select format was announced. This is an ordinary Memory Stick card, but inside it there were two memory chips of 128 MB each. And it was possible to switch between them using a special switch on the card itself. Not a very convenient solution. Therefore, it was temporary and intermediate.

The low capacity was overcome with the release of Memory Stick PRO in 2003. Theoretically, such a memory card can store up to 32 GB of data, but in practice, more than 4 GB did not. Of course, most older devices do not recognize the PRO version, but new ones can easily recognize the first generation Memory Stick. Even more confusing is a sub-variant of the High Speed ​​Memory Stick PRO standard. These were all Memory Stick PRO with a capacity of 1 GB. It is clear that they could work in a special high-speed mode. And I'm very glad that they are all backwards compatible with older devices, just that the speed dropped to normal.

Over time, it became clear that it would be necessary to follow the path of reducing the cards, otherwise the "plates" of the Memory Stick are far from being convenient to use everywhere. This is how the Memory Stick Duo appeared, 31x20x1.6 mm in size - slightly smaller than Secure Digital. But bad luck, these cards were based on the first version of the Memory Stick standard, and with it a limit on the maximum volume. 128 MB for 2002 is somehow not solid at all. And so the Memory Stick PRO Duo was born in 2003. And it is this standard that is developing the most today - there are already 16 GB cards, 32 GB options are on the way, and the theoretical limit, according to Sony, is 2 TB.

In December 2006, Sony, together with SanDisk, announced a new modification of their flash memory cards - Memory Stick PRO-HG Duo. Its main difference from other options is a higher speed. In addition to the 4-bit communication interface, an 8-bit one has been added. Yes, and the controller frequency has risen from 40 to 60 MHz. As a result, the theoretical speed limit increased to 480 Mbps or 60 Mbps.

Well, following the latest fashion, in February 2006, the Memory Stick Micro card format (or it is also called M2) appeared, with dimensions of 15x12.5x1.2 mm - this is a little more microSD. Their capacity varies from 128 to 16 GB, and theoretically can be 32 GB. Through an adapter, an M2 memory card can be inserted into the Memory Stick PRO slot, but if its capacity is more than 4 GB, then certain recognition problems may occur.

Here is such a squiggle. If you look, then in principle it is not difficult: Memory Stick - the original format is not the most compact size, Memory Stick PRO - an option with a larger capacity and speed, Memory Stick (PRO) Duo - a smaller version of cards, Memory Stick PRO-HG Duo - an accelerated version of Memory Stick PRO Duo, Memory Stick Micro (M2) are the smallest Memory Sticks. Now you can go to the latest standard - xD.

xD-Picture Card

Olympus and Fujifilm felt that the flash card formats that existed in the early years of this century did not match their vision of an ideal data storage for cameras. How else to explain the development of its own xD-Picture Card standard?

From the name of the format it follows that it was created for storing images. But Olympus produces digital voice recorders based on it, and Fujitsu - MP3 players. However, there are far fewer recent devices than xD-enabled cameras. However, if we compare the total sales of Fujitsu and Olympus digital cameras, they will not surpass the figures of the market leaders - Canon and Nikon. And the leaders calmly use CompactFlash in mid-range and high-end SLR cameras, while the rest have taken root with the Secure Digital standard. Well, since the distribution of xD cards is not very large, then in their development they lag behind the most popular formats, and besides, they are more expensive. Approximately 2-3 times, if you take cards of the same capacity.

Obviously, the main orientation of the developers of the xD format (by the way, Toshiba and Samsung are producing cards based on it) was to reduce the size of the memory card. Its dimensions are as follows - 20x25x1.78 mm. About like two Memory Stick Micro.

The capacity of the very first version of xD cards varies from 16 to 512 MB. They were introduced in July 2002. However, in February 2005, the first update appeared, which made it possible to increase the maximum volume to 8 GB. The new standard was called xD Type M. It was possible to increase the volume through the use of MLC memory, which at the same time turned out to be slower. Type M xD cards have reached 2 GB. And so far, neither Type M nor newer standards have overcome this limit.

To solve the speed problem, xD Type H was introduced in November 2005. This format was based on SLC memory, since it was decided to stop production in 2008 due to high cost. But to replace him in April 2008, the Type M + was released. Cards of this format are about 1.5 times faster than Type M.

Backward compatibility of different versions of xD formats is true only for the newest devices - they easily recognize older versions of cards. But old devices do not necessarily recognize new cards. This is about the same situation as with other standards.

In terms of speed, as in terms of volume, xD does not shine at all. Today, the average Type M+ read speed is 6.00 MB/s (40x) and write speed is 3.75 MB/s (25x).

In total, the xD-Picture Card format is more expensive in retail than SD and CF. Memory cards are quite compact, but their capacity no longer meets modern requirements. The same applies to the speed of work. For shooting video with a resolution of 640x480 at 30 frames per second, Type M + is still enough. But for today's SLR cameras that shoot 12-24 MP frames and 720p and 1080p video, this is clearly not enough. It's not bad at all to have a card for 200-300x. So we don't see much point in continuing to support and develop xD. We won’t be surprised if they suddenly decide to cover it up, and the next generation of cameras will be transferred to SD and / or CF.

The abbreviation SSD began to appear in news feeds and article titles relatively recently - a couple of years ago. The reason for this is that this technology began to become mass-produced only when flash memory was increasingly used for data storage, and the mentioned headlines (and text) of the news kept talking about the imminent rapid growth of this market, along the way promising to replace the HDD. At least from the segment of laptops and netbooks.

But the most interesting thing is that an SSD is not necessarily a flash-based drive. SSD or Solid State Drive stands for Solid State Drive. That is, the principle is more important here than the type - "hard" memory is used to store data. A memory that doesn't spin, spin, or jump. So the SSD is not a couple of years at all, but formally fifty years. Then this technology was called differently, but again, the principle is important here. But the principle has been preserved.

Today, two types of SSD are relevant: based on volatile memory and based on non-volatile memory. The first are those that use SRAM or DRAM memory as their basis. They are also called RAM drives. From time to time, such SSDs are announced by manufacturers as ultra-fast storage media. Some of them even allow you to increase the volume on your own, when the board has connectors for ordinary memory modules (DDR, DDR2 or DDR3 in the most modern version).

Well, non-volatile memory is, of course, flash. It has long been possible to create an SSD based on it, but the volumes of such drives were far from the capabilities of hard drives, and the cost was much higher. Yes, and the speed did not shine. But today these shortcomings are gradually eliminated.

The first generation of SSD had a capacity of 16 to 64 GB, and such "flash drives" cost hundreds and thousands of dollars. This was about two years ago. Today, options are available for 64-512 GB at a price of $200-1500. It's far from hard drives, but it's already much better. Behind and on the way is a 1TB SSD in 2.5-inch hard drive format. Recall that mobile HDD has not yet exceeded the volume of 500 GB. And the desktop ones have just reached the 2 TB mark. So SSD is moving forward by leaps and bounds.

As for the speed of work, it is also constantly growing. The first generation of SSDs lagged somewhat behind mobile hard drives, but today's drives have surpassed them. Suffice it to recall the Intel X25-M SSD introduced last year, which has a read speed of 250 MB / s, and a write speed of 70 MB / s. And it costs not like a flight to the ISS - about $ 350 with a volume of 80 GB.

Of course, there are super-fast models from Fusion-IO with read/write speeds of 800/694 MB/s or PhotoFast G-Monster PCIe SSD with 1000/1000 MB/s, but they are priced like a small jet. And of course, they use not SerialATA for data exchange, but a regular PCI Express x8 - this standard is still able to provide the required bandwidth. By the way, PCI Express x1 is actively used to connect SSDs in netbooks. It is in this format that their data storages are made - in the form of a small PCI-E x1 board.

Such high speed performance for SSDs was achieved due to the parallel reading of data from several chips at once. For example, the Intel X25-M mentioned above works on the principle of a RAID level 0 array. That is, one bit is written to the first chip, the second to the second, and so on. It is extremely difficult to organize such a mechanism for a regular USB flash drive or memory card, since they almost always have only one flash memory chip installed.

To increase capacity and reduce cost, SSDs often use MLC memory (including the X25-M). More expensive models are equipped with SLC chips. But if you write data relatively rarely to a USB flash drive or some SD card, then recording to an SSD is continuous during operation. And in most cases, you don't even know it. Modern programs constantly keep various logs; the operating system moves little-used data to the swap file, thus freeing up RAM; even a rudimentary file access requires a record of the access time.

So in any case, you have to install more durable chips in the SSD. You also have to worry about the algorithms for calculating the level of wear and data redistribution - they must be more advanced than conventional flash drives. SSD drives even have an additional volatile cache memory chip, just like a regular hard drive. The cache contains data on block addresses and data on wear levels. When turned off, the latter are saved to flash memory.

In any case, for now, flash-based SSD technology continues to develop rapidly. It offers several undeniable advantages over HDD:

• significantly lower data access time;
• constant data reading speed;
• zero noise level;
• less power consumption.

At the moment, it remains to bring the number of rewriting cycles to such an amount that you can not worry about it at all. The capacity will keep growing. It is possible that in the next 2-3 years it will overtake and even overtake hard drives. Well, the price falls by itself, if the technology is promising, actively promoted and the level of sales is constantly growing. We don't know if SSD will be able to replace HDD in the desktop market, but they are already aiming at mobile ones.

Future

Actually, we've come to the end. The conclusion from the above can be drawn as follows: flash memory in the future will be increasingly distributed and improved. It is not yet clear whether she can replace the hard drives, but she has the makings of this. But there is another snag - the file system.

Modern file systems are optimized for use with hard drives. But an HDD is not an SSD at all in its structure. First of all, access to data on the hard drive is carried out using LBA addressing. The block of such an address allows you to calculate on which plate, on which track and in which sector the requested information is located. But here's the problem - flash does not have plates, tracks and sectors. But there are blocks divided into pages. Today, this problem is solved by translating addresses from one format to another, but it would be much more convenient if all this happened directly.

Another feature of flash memory is that it can only be written to previously cleared blocks. And this operation takes some time. So it would be nice to clear completely unused blocks during downtime.

Modern disk file systems are optimized to minimize data access time - they try to search for them as quickly as possible across the disk. But for flash memory, this is simply irrelevant - access to all blocks is equally fast. Well, support for calculating the level of wear of flash chips from the file system will not hurt.

So the matter of the near future is the release of new file systems optimized for working with flash memory. Such, however, already exist, but modern operating systems do not support them well. It is noteworthy that one of the first was FFS2 from Microsoft, which she released back in the early 90s.

Linux OS keeps up with the progress. The JFFS, JFFS2, YAFFS, LogFS, UBIFS file systems were created for it. Sun also distinguished itself by developing ZFS, which recently . It is optimized not only for hard drives, but also for flash drives. Moreover, both for using them as the main storage, and as a cache.

However, today the most popular file system for flash drives (not counting SSDs) remains FAT and FAT32. It's just the most convenient. They are supported by all operating systems and do not require drivers. But they are no longer enough to work. For example, the limit on the maximum file size (4 GB) is already becoming unacceptable.

However, Microsoft has a replacement - exFAT, formerly known as FAT64. As we already wrote, it is chosen as the main FS for SDXC cards. In addition to being optimized for flash memory, it supports files up to 16 exabytes (16.7 million terabytes) in size, and more than 65536 files can be stored in one folder.

exFAT is supported today by Windows Mobile version 6.0 and later, Windows XP SP2 and later, Windows Vista SP1, Windows Server 2008, and Windows 7 from build 6801. ReadyBoost functions. Appropriate support will appear in Windows 7. As for other operating systems, a free kernel module is available for Linux that allows you to use exFAT read-only.

So the most promising OS for flash drives today looks like ZFS and exFAT. But both are very poorly distributed, although the latter is more likely to become popular. It has already been chosen as the main one for the latest generation of SD cards, and all the most popular versions of Windows "know" it.

As for the rest, we will wait for a further increase in the capacity of flash drives and a decrease in their cost. This technology is very good, so we wish it only success.