Data storage devices are intended for storing electronic information. Depending on their design features, they are divided into several types, the most common of which are flash drives. They have become widespread due to their small physical dimensions and impressive volume, which allows them to store a large number of files. However, when purchasing a flash drive, each user was faced with a situation where the usable capacity of the drive did not correspond to what was declared by the manufacturer. Why does this situation arise?

Definition of Flash Memory

Flash memory is one of the types of modern information storage devices, which is based on electrical programming technology, which allows you to obtain a completely complete, from a technological point of view, solution for recording and storing electronic information.
Regular users use the term “flash memory” to classify a large category of information storage devices that are manufactured using this technology. The main advantages of this category of data storage devices are:

— Small dimensions;
- Low cost;
— Excellent resistance to mechanical damage;
— Large volume;
— High speed of data reading;
— Low power consumption.

Thanks to all the above advantages, this type of memory has found wide application in the production of various electronic gadgets, as well as external data storage devices. However, there are also significant disadvantages that flash memory has. The main ones are the fragility of operation and increased sensitivity to electrostatic discharges.

What about the amount of memory that modern flash drives can have? There is no definite answer to this question, since just a few years ago 128 gigabytes seemed to be the limit, and today no one is surprised by flash drives capable of storing one terabyte of information. And this is far from the limit.

A little history

The first data storage devices in this category are considered to be hard drives, in which the recording process was carried out using electrical discharges, and erasing was carried out using ultraviolet light. LED floating-gate transistors were used as storage elements in such media. The information of these permanent storage devices was represented in the form of an electrical discharge, which was attached to a dielectric. The main problem with these devices was the very large wiring area, which was reduced only in 1984. It was then that the first modern flash drives appeared.

Principle of operation

Recording and storing information electronically on flash drives occurs by registering and changing the electrical charge of LED transistors. This process is based on the principle of the tunnel effect, which occurs between the source of electricity and the moving gate of the transistor. To increase the efficiency of this process, electron acceleration is used. Reading of the recorded information is carried out using field-effect transistors. To implement work with a large number of information cells, special elements are implemented in the flash memory design. The small physical dimensions of drives of this class and the large amount of memory are achieved thanks to the small size of all electronic elements included in these devices.

NOR and NAND devices

These elements differ depending on the method that underlies the implementation of a large array of sources for storing electrical charges, as well as the technology for recording and reading information. Devices of the NOR category are created on the basis of a two-dimensional semiconductor matrix, at the intersection of which one cell is used. In the process of writing and reading electronic information, one output of the cell is in contact with the transistor, and the second is in contact with the gate of the columns. The source is in contact with the substrate, which acts as a connecting link for all elements of the flash drive. This design allows you to supply power to one transistor, which stores the necessary part of the information.

Unlike the NOR structure, NAND class devices operate on the principle of a three-dimensional array. Drives with these devices are created on the same type of matrix, with the only exception that at the intersection of transistors, not one, but a column of consecutive cells is based. Thus, a large number of gate circuits can be located at one intersection, which makes it possible to significantly increase the number of elements included in the basis of information storage devices. However, this leads to a significant complication of the algorithm for accessing electronic elements that store electronic charge, as well as the process of writing and reading information. Nevertheless, despite the more complex design, flash drives developed on these devices have a significantly larger capacity.

SLC and MLC devices

Some devices used in the production of flash storage devices are capable of simultaneously storing several bits of information instead of just one. This is achieved by increasing the number of charges that the floating gate of transistors can simultaneously store. Such devices are called multi-bit or multi-level, and in technical documentation they are designated as MLC. It is worth noting that despite the advantages in operation, they have a lower cost, however, there is also a negative side, for example, a smaller resource of rewrite cycles, which significantly reduces their service life.

Audio memory

As technological progress developed and MLC devices were invented, technicians came up with the idea of ​​​​converting an analog signal into an electrical signal, and then recording it in a flash memory cell. This idea has been put into practice, and the most striking example is various children's toys that can reproduce sounds.

Technological limitations

During the operation of flash memory, information is regularly written and read. At the same time, the energy costs for both of these processes are very different. In order to write electronic data into a cell, more electricity is needed than to read it.

Information recording and storage resource

In the process of placing an electric charge into a transistor cell, irreversible changes in the structure of these elements occur. In turn, each transistor has a limited number of write cycles. The maximum number of cycles depends on the manufacturing technologies used, as well as the parts used. This is explained by the fact that it is impossible to control the electrical charge placed in the floating gate, therefore, as the drive is used, the structure of the transistor is damaged and the electrical charge is lost.

The same trend is observed in the maximum time for which a charge can be stored. On average, electronic information can be stored on flash drives for 10 to 20 years, however, these periods may vary depending on the technologies and elements used in production.

Physics,

Electronics for Beginners

Preface

New Year is a pleasant, bright holiday on which we all sum up the past year, look to the future with hope and give gifts. In this regard, I would like to thank all Habr residents for their support, help and interest shown in my articles (, , ,). If you had not once supported the first one, there would not have been any subsequent ones (already 5 articles)! Thank you! And, of course, I want to give a gift in the form of a popular scientific article about how you can use analytical equipment that is quite harsh at first glance in a fun, interesting and beneficial way (both personal and social). Today, on New Year's Eve, on the festive operating table are: a USB-Flash drive from A-Data and a SO-DIMM SDRAM module from Samsung.

Theoretical part

I’ll try to be as brief as possible so that we all have time to prepare Olivier salad with extra for the holiday table, so some of the material will be in the form of links: if you want, you can read it at your leisure...

What kind of memory is there?

At the moment, there are many options for storing information, some of them require constant power supply with electricity (RAM), some are forever “sewn” into the control chips of the equipment around us (ROM), and some combine the qualities of both and others (Hybrid). Flash, in particular, belongs to the latter. It seems to be non-volatile memory, but the laws of physics are difficult to cancel, and from time to time you still have to rewrite information on flash drives.

The only thing that, perhaps, can unite all these types of memory is more or less the same operating principle. There is some two-dimensional or three-dimensional matrix that is filled with 0s and 1s in approximately this way and from which we can subsequently either read these values ​​or replace them, i.e. all this is a direct analogue of its predecessor - memory on ferrite rings.

What is flash memory and what types does it come in (NOR and NAND)?

Let's start with flash memory. Once upon a time, the well-known ixbt published quite a bit about what Flash is and what the 2 main types of this type of memory are. In particular, there are NOR (logical not-or) and NAND (logical not-and) Flash memory (everything is also described in great detail), which are somewhat different in their organization (for example, NOR is two-dimensional, NAND can be three-dimensional), but they have one common element - a floating gate transistor.

Schematic representation of a floating gate transistor.

So how does this engineering marvel work? This is described together with some physical formulas. In short, between the control gate and the channel through which current flows from source to drain, we place the same floating gate, surrounded by a thin layer of dielectric. As a result, when current flows through such a “modified” field-effect transistor, some high-energy electrons tunnel through the dielectric and end up inside the floating gate. It is clear that while the electrons were tunneling and wandering inside this gate, they lost some of their energy and practically cannot return back.

NB:“practically” is the key word, because without rewriting, without updating cells at least once every few years, Flash is “reset to zero” just like RAM, after turning off the computer.

Again we have a two-dimensional array that needs to be filled with 0s and 1s. Since it takes quite a long time to accumulate charge on the floating gate, a different solution is used in the case of RAM. The memory cell consists of a capacitor and a conventional field-effect transistor. Moreover, the capacitor itself has, on the one hand, a primitive physical device, but, on the other hand, it is non-trivially implemented in hardware:

RAM cell design.

Again, ixbt has a good one dedicated to DRAM and SDRAM memory. It is, of course, not so fresh, but the fundamental points are described very well.

The only question that torments me is: can DRAM have a multi-level cell, like flash? It seems like yes, but still...

Practical part

Flash

Those who have been using flash drives for quite some time have probably already seen a “bare” drive, without a case. But I will still briefly mention the main parts of a USB flash drive:

The main elements of a USB Flash drive: 1. USB connector, 2. controller, 3. PCB-multilayer printed circuit board, 4. NAND memory module, 5. quartz reference frequency oscillator, 6. LED indicator (now, however, on many flash drives do not have it), 7. write protection switch (similarly, it is missing on many flash drives), 8. space for an additional memory chip.

Let's go from simple to complex. Crystal oscillator (more about the principle of operation). To my deep regret, during the polishing the quartz plate itself disappeared, so we can only admire the body.

Crystal oscillator housing

By chance, in the meantime, I found what the reinforcing fiber inside the PCB looks like and the balls that make up the PCB for the most part. By the way, the fibers are still laid with twisting, this is clearly visible in the top image:

Reinforcing fiber inside the PCB (red arrows indicate fibers perpendicular to the cut), which makes up the bulk of the PCB

And here is the first important part of the flash drive - the controller:

Controller. The top image was obtained by combining several SEM micrographs

To be honest, I didn’t quite understand the idea of ​​the engineers who placed some additional conductors in the chip itself. Maybe this is easier and cheaper to do from a technological point of view.

After processing this picture, I shouted: “Yayyyyyyyyyyyyyyyyyyyyyyy!” and ran around the room. So, we present to your attention the 500 nm technological process in all its glory with perfectly drawn boundaries of the drain, source, control gate, and even the contacts are preserved in relative integrity:

"Ide!" microelectronics - 500 nm controller technology with beautifully drawn individual drains (Drain), sources (Source) and control gates (Gate)

Now let's move on to dessert - memory chips. Let's start with the contacts that literally feed this memory. In addition to the main one (the “thickest” contact in the picture), there are also many small ones. By the way, "fat"< 2 диаметров человеческого волоса, так что всё в мире относительно:

SEM images of the contacts powering the memory chip

If we talk about memory itself, then success awaits us here too. We were able to photograph individual blocks, the boundaries of which are indicated by arrows. Looking at the image with maximum magnification, try to strain your gaze, this contrast is really difficult to discern, but it is there in the image (for clarity, I marked a separate cell with lines):

Memory cells 1. Block boundaries are marked with arrows. Lines indicate individual cells

At first it seemed to me like an image artifact, but after processing all the photos of the house, I realized that these are either control gates elongated along the vertical axis in an SLC cell, or these are several cells assembled in an MLC. Although I mentioned MLC above, this is still a question. For reference, the "thickness" of the cell (i.e. the distance between the two light dots in the bottom image) is about 60 nm.

In order not to dissemble, here are similar photos from the other half of the flash drive. A completely similar picture:

Memory cells 2. Block boundaries are highlighted with arrows. Lines indicate individual cells

Of course, the chip itself is not just a set of such memory cells; there are some other structures inside it, the identity of which I could not determine:

Other structures inside NAND memory chips
 

DRAM

Of course, I didn’t cut the entire SO-DIMM board from Samsung; I only “disconnected” one of the memory modules using a hair dryer. It is worth noting that one of the tips proposed after the first publication came in handy here - sawing at an angle. Therefore, for a detailed immersion in what you saw, it is necessary to take this fact into account, especially since cutting at 45 degrees also made it possible to obtain, as it were, “tomographic” sections of the capacitor.

However, according to tradition, let's start with contacts. It was nice to see what a “chipped” BGA looks like and what the soldering itself is like:

"Chipped" BGA solders

And now it’s time to shout “Ide!” for the second time, since we managed to see individual solid-state capacitors - concentric circles in the image, marked with arrows. They are the ones who store our data while the computer is running in the form of a charge on their plates. Judging by the photographs, the dimensions of such a capacitor are about 300 nm in width and about 100 nm in thickness.

Due to the fact that the chip is cut at an angle, some capacitors are cut neatly in the middle, while others have only the “sides” cut off:

DRAM memory at its finest

If anyone doubts that these structures are capacitors, then you can look at a more “professional” photo (though without a scale mark).

The only point that confused me is that the capacitors are located in 2 rows (lower left photo), i.e. It turns out that there are 2 bits of information per cell. As mentioned above, information on multibit recording is available, but to what extent this technology is applicable and used in modern industry remains questionable to me.

Of course, in addition to the memory cells themselves, there are also some auxiliary structures inside the module, the purpose of which I can only guess:

Other structures inside a DRAM memory chip

Afterword

In addition to those links that are scattered throughout the text, in my opinion, this review (even from 1997), the site itself (and a photo gallery, and chip-art, and patents, and much, much more) and this office, which actually engaged in reverse engineering.

Unfortunately, it was not possible to find a large number of videos on the topic of Flash and RAM production, so you will have to be content with only assembling USB Flash drives:

P.S.: Once again, Happy New Year of the Black Water Dragon everyone!!!
It turns out strange: I wanted to write an article about Flash one of the first, but fate decreed otherwise. Fingers crossed, let's hope that the next at least 2 articles (about biological objects and displays) will be published in early 2012. In the meantime, the seed is carbon tape:

Carbon tape on which the samples under study were attached. I think regular tape looks similar.

Flash memory is a type of long-lasting memory for computers in which the contents can be reprogrammed or electrically erased. Compared to Electrically Erasable Programmable Read Only Memory, operations on it can be performed in blocks that are located in different places. Flash memory costs much less than EEPROM, which is why it has become the dominant technology. Particularly 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 for the 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 fame in the world of gamers, where it is often used to store game progress data.

general description

Flash memory is a type that is capable of storing information on its board for a long time without using power. In addition, we can note the highest data access speed, as well as better 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 rechargeable batteries. Another undeniable 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 way to access data residing in flash memory is very different from that of conventional types. 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 about it.

Design and principle of operation

At the moment, flash memory is widespread, which is created on single-transistor elements with a “floating” gate. This makes it possible to provide greater data storage density compared to dynamic RAM, which requires a pair of transistors and a capacitor element. At the moment, the market is replete with various technologies for constructing basic elements for this type of media, which are developed by leading manufacturers. They are distinguished by 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.

Currently, there are a couple of types of chips 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 fairly large cell sizes and allows for fast random access, allowing 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 amounts of information will be stored.

In most portable devices, the SSD uses the NOR memory type. However, devices with a USB interface are becoming increasingly popular. They use NAND memory. Gradually it displaces the first one.

The main problem is 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 medium. Due to the design of flash memory, it allows erasing and writing of information in 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 binary. Writing and erasing data in NAND memory is carried out using tunneled electrons using the Fowler-Nordheim method with the participation of a dielectric. This does not require what allows you to make cells of minimal sizes. But it is this process that leads to cells, since the electric current in this case forces electrons to penetrate the gate, overcoming the dielectric barrier. However, the guaranteed shelf life of such memory is ten years. 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 solid-state drives of this type: they are striving to ensure uniformity of writing/erasing processes across the cells of the array, so that some do not wear out more than others. To distribute the load evenly, software paths are predominantly used. For example, to eliminate this phenomenon, “wear leveling” technology is used. In this case, data that is often subject to changes is moved to the address space of flash memory, so 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 various models, since implementation details are not disclosed. Since the volume of flash drives is becoming larger every year, it is necessary to use more and more efficient operating algorithms to guarantee the stable functioning of the devices.

Troubleshooting

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

And other types of similar drives are characterized by the fact that a table with a 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 caching when using removable devices, frequent rewriting has the most detrimental effect on the file allocation table and directory table of contents. And even special programs for memory cards are not able to help in this situation. For example, during a one-time request, the user overwrote a thousand files. And, it would seem, I only used the blocks where they were located for recording once. But service areas were rewritten 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 data will fail first. Wear leveling technology also works with such blocks, but its effectiveness is very limited. And it doesn’t matter what kind of computer you use, the flash drive will fail exactly when the creator intended it to.

It is worth noting that the increase in the capacity of the microcircuits of such devices has only led to the fact that the total number of write cycles has decreased, since the cells are becoming 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 the increase in the capacity of the devices used, the problem of their reliability began to worsen more and more, 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 production costs by any means. Including due to simplified design, the use of components from a cheaper set, weakening control over production and other methods. For example, a Samsung memory card will cost more than its lesser-known analogues, but its reliability raises much fewer questions. But even here it is difficult to talk about a complete absence of problems, and it is difficult to expect anything more from devices from completely unknown manufacturers.

Development prospects

While there are obvious advantages, there are a number of disadvantages that characterize the SD memory card, which prevent 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 are trying to improve 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: companies engaged 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 volumes, so it is assumed that it will continue to be actively sold out.

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

Ferroelectric RAM (FRAM)

The technology of the ferroelectric principle of information storage (Ferroelectric RAM, FRAM) 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 during the reading process 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 in operation. These properties are now characteristic of DRAM - non-volatile random access memory that currently exists. But here we will also add the possibility of long-term data storage, which is characterized by Among the advantages of such technology, we can highlight resistance to various types of penetrating radiation, 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 here is implemented 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 sandwiching an ultra-thin film of ferroelectric material in the form of crystals between a pair of flat metal electrodes, forming 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. Data in FRAM memory is retained even when the power supply is turned off.

Magnetic RAM (MRAM)

Another type of memory that is considered very promising today is MRAM. It is characterized by fairly high speed performance and energy independence. in this case, a thin magnetic film placed on a silicon substrate is used. MRAM is static memory. It does not need periodic rewriting, and 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 a 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 using a specialized CMOS process. And MRAM chips can be produced using a standard manufacturing process. Moreover, the materials can be those used in conventional magnetic media. It is much cheaper to produce large quantities of such microcircuits than all the others. An important property of MRAM memory is its instantaneous turn-on capability. 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 electrical charge, as in traditional flash memory.

Ovonic Unified Memory (OUM)

Another type of memory that many companies are actively working on is a solid-state drive based on amorphous semiconductors. It is based on phase change technology, which is similar to the principle of recording on conventional discs. Here the phase state of a substance 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 disks in that heating occurs due to the action of 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 disk drive sensor. Theoretically, such a solution has a high data storage density and maximum reliability, as well as increased performance. The maximum number of rewrite cycles is high here, for which a computer is used; a 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 principle that in one phase the substance used in the carrier acts as a non-conducting amorphous material, and in the second it serves as a crystalline conductor. The transition of a memory 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 and transferred to a hologram using CGH technology. Data is read by fixing the laser beam on the edge of one of the recorded layers, which serve as optical waveguides. The 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 cost of storage media, environmental safety and protection from unauthorized use. But such a memory card does not allow rewriting of information, so it can only serve as long-term storage, a replacement for paper media, or an alternative to optical disks for distributing multimedia content.

The basic design of the device has remained unchanged since 1995, when flash drives first began to be produced on an industrial scale. Without going into details, a USB flash card consists of three key elements: * USB connector - a connector well known to everyone, which is an interface between a flash drive and a computer system, be it a personal computer system, a multimedia center or even a car radio; * memory controller is a very important element of the circuit. Connects the device memory with the USB connector and manages data transfer in both directions; * memory chip is the most expensive and important part of a USB flash card. Determines the amount of information stored on the card and the speed of reading/writing data. What can change in this scheme? Nothing in principle, but modern industry provides several options for such a scheme; combination of eSATA and USB connectors, two USB connectors.

1 -- USB connector; 2 -- microcontroller; 3 -- control points; 4 -- flash memory chip; 5 -- quartz resonator; 6 -- LED; 7 -- "write protection" switch; 8 -- space for an additional memory chip.

Operating principle

Flash memory stores information in an array of floating-gate transistors called cells. In traditional devices with single-level cells (English single-level cells, SLC), each of them can store only one bit. Some new multi-level cell (MLC; triple-level cell, TLC) devices can store more than one bit by using different levels of electrical charge on a transistor's floating gate.

Types of flash memory

NOR

This type of flash memory is based on a NOR gate because in a floating gate transistor, a low gate voltage denotes a one.

The transistor has two gates: control and floating. The latter is completely isolated and is capable of retaining electrons for up to 10 years. The cell also has a drain and a source. When programming with voltage, an electric field is created at the control gate and a tunnel effect occurs. Some electrons tunnel through the insulator layer and reach the floating gate. The charge on the floating gate changes the "width" of the drain-source channel and its conductivity, which is used for reading.

Programming and reading cells have very different power consumption: flash memory devices consume quite a lot of current when writing, while the energy consumption is low when reading.

To erase information, a high negative voltage is applied to the control gate, and electrons from the floating gate move (tunnel) to the source.

In the NOR architecture, each transistor must be connected to an individual contact, which increases the size of the circuit. This problem is solved using NAND architecture.

NAND

The NAND type is based on the NAND element. The operating principle is the same; it differs from the NOR type only in the placement of the cells and their contacts. As a result, it is no longer necessary to make an individual contact to each cell, so the size and cost of the NAND chip can be significantly reduced. Also writing and erasing is faster. However, this architecture does not allow access to an arbitrary cell.

NAND and NOR architectures now exist in parallel and do not compete with each other, since they are used in different areas of data storage.

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

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

Flash memory is a type of solid-state, non-volatile, rewritable memory. Unlike a hard drive, a flash drive has a high read speed, which can reach up to 100 MB/s, and is very small in 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 turned off, autonomously.

Today, flash drives with capacities ranging from 256 megabytes to 16 gigabytes are available on the market. But there are media with a larger volume.

Additional flash memory functions 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.

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 this type of memory to be used very widely. These include 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 fairly 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 CompactFlash (CF), there are two types CF type I and CF type II. Has good speed, capacity and price.
The disadvantages include the size 42*36*4 mm. It is quite versatile and is used in many devices.

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

SmartMedia- thin and cheap, but not high protection against abrasion.

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

Secure Digital (SD) with comparable dimensions to the Multimedia Card, it has greater capacity and speed. But more expensive.

MemoryStick- 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 cards listed, there are other types of flash cards

You should choose a flash card based on your needs, taking into account that the larger the capacity and speed, the more expensive the flash card.