That means flash memory. Pci flash memory what is it - flash memory capacity. Plunging into history
In this article, we will talk about what is the basis for its creation and on what principle a flash memory device works (do not confuse it with USB flash drives and memory cards). In addition, you will learn about its advantages and disadvantages over other types of ROM (read-only memory devices) and get acquainted with the range of the most common drives that contain flash memory.
The main advantage of this device is that it is non-volatile and does not require electricity to store data. All information stored in flash memory can be read an infinite number of times, but the number of complete write cycles is unfortunately limited.
Flash memory refers to electrically reprogrammable memory (EEPROM) semiconductors. Thanks to technical solutions, low cost, large volume, low power consumption, high speed, compactness and mechanical strength, flash memory is built into digital portable devices and storage media.
Flash memory has both its advantages and disadvantages over other ROM-type drives (hard drives and optical drives), which you can see in the table below.
| ROM type | Advantages | Flaws |
| Hard drive | Large amount of stored information. High speed. Cheap data storage (per 1 MB). | Large dimensions. Sensitivity to vibration. Heat dissipation. |
| Optical disc | Ease of transportation. Cheap information storage. Possibility of replication. | Small volume. You need a reader. Restrictions on operations (read, write). Low operating speed. Sensitivity to vibration. |
| Flash memory | High speed data access. Economical energy consumption. Vibration resistance. Ease of connection to a computer. Compact sizes. | Limited number of write cycles. |
Today, no one doubts that flash memory will continue to strengthen its position in information technology, especially in the line of mobile devices (PDAs, tablets, smartphones, players). The most popular and popular and replaceable memory cards for electronic devices (SD, MMC, miniSD...) are based on flash memory.
Memory cards, like USB drives, do not stand aside, but attract the attention of potential buyers with their diversity. From such an abundance of storage devices, only the manufacturer benefits, while the consumer experiences a number of inconveniences. After all, we are all familiar with such situations when a phone needs one card, a PDA another, and a camera a third. This assortment of drives benefits manufacturers because they benefit greatly from wide exclusive sales. Here is a small list of common flash memory drives:
- Compact Flash Type I (CF I)/Type II (CF II);
- Memory Stick (MS Pro, MS Duo);
- Secure Digital (SD);
- miniSD;
- xD-Picture Card (xD);
- MultiMedia Card (MMC).
- USB Flash Drive.
In one of the publications, I wrote about how to choose a card in SD format (microSD, miniSD).
The principle of operation of flash memory.
The basic data storage cell of flash memory is a floating gate transistor. The peculiarity of such a transistor is that it can hold electrons (charge). It is on this basis that the main types of flash memory have been developed. NAND And NOR. There is no competition between them, because each type has its own advantages and disadvantages. By the way, hybrid versions are built on their basis, such as DiNOR And superAND.
In flash memory, manufacturers use two types of memory cells: MLC and SLC.
- Flash memory with MLC (Multi-level cell - multi-level memory cells) cells are more capacious and cheaper, but they have longer access times and fewer write/erase cycles (about 10,000).
- Flash memory, which contains SLC (Single-level cell) cells, has a maximum number of write/erase cycles (100,000) and has shorter access times.
Charge reversal (write/erase) is accomplished by applying a high potential between the gate and source so that the electric field strength in the thin dielectric between the transistor channel and the pocket is sufficient to produce a tunneling effect. To enhance the effect of electron tunneling into the pocket during writing, a slight acceleration of the electrons is applied by passing a current through the field-effect transistor channel.
The operating principle of flash memory is based on changing and recording the electrical charge in an isolated region (“pocket”) of the semiconductor structure.
Reading is performed by a field-effect transistor, for which the pocket acts as a gate. The floating gate potential changes the threshold characteristics of the transistor, which is recorded by the read circuits. This design is equipped with elements that allow it to work in a large array of the same cells.
Now let's take a closer look at memory cells with one and two transistors...
Memory cell with one transistor.
If a positive voltage is applied to the control gate (initializing a memory cell), it will be in the open state, which will correspond to a logical zero.
And if on floating shutter place an excess negative charge (electron) and apply a positive voltage to control gate, then it compensates for the electric field created by the control gate and will not allow a conduction channel to form, which means the transistor will be in the closed state.
So, the presence or absence of charge on the floating gate accurately determines the open or closed state of the transistor when the same positive voltage is applied to the control gate. If we consider applying voltage to the control gate as initializing a memory cell, then by the voltage between the source and drain we can judge the presence or absence of charge on the floating gate.
In this way, a kind of elementary memory cell is obtained, capable of storing one information bit. In addition to all this, it is very important that the charge on the floating gate (if there is one) can remain there for a long time, both during initialization of the memory cell and in the absence of voltage on the control gate. Only in this case will the memory cell be non-volatile.
So how, if necessary, place a charge on a floating gate (write the contents of a memory cell) and remove it from there (erase the contents of a memory cell) when necessary.
A charge can be placed on the floating gate (recording process) using the hot electron injection method (CHE-Channel Hot Electrons) or the Fowler-Nordheim tunneling method.
If the hot electron injection method is used, then a high voltage is applied to the drain and control gate, which will give the electrons in the channel energy sufficient to overcome the potential barrier created by a thin layer of dielectric and be directed (tunneled) into the floating gate region (during reading on the control gate is supplied with less voltage and the tunneling effect does not occur).
To remove charge from the floating gate (perform a memory cell erase), a high negative voltage (about 9 V) is applied to the control gate, and a positive voltage is applied to the source region. This causes electrons to tunnel from the floating gate region to the source region. This is how Fowler-Nordheim quantum tunneling occurs.
You probably already realized that a floating gate transistor is a basic flash memory cell. But single-transistor cells have some disadvantages, the main one being poor scalability.
Since when creating a memory array, each memory cell (that is, a transistor) is connected to two perpendicular buses. The control gates are connected to a bus called the Word Line, and the drains are connected to a bus called the Bit Line. As a result, there is a high voltage in the circuit and when recording using the hot electron injection method, all lines - words, bits and sources - must be placed at a great distance from each other. This will give the desired level of isolation, but will affect the limitation of flash memory capacity.
Another disadvantage of such a memory cell is the presence of the effect of excessive charge removal from the floating gate, and it cannot be compensated by the recording process. As a result, a positive charge is formed on the floating gate, which makes the state of the transistor unchanged and it always remains open.
Memory cell with two transistors.
A two-transistor memory cell is a modified single-transistor memory cell that contains a conventional CMOS transistor and a floating gate transistor. In this structure, a conventional transistor acts as a floating gate transistor insulator from the bit line.
Does a two-transistor memory cell have any advantages? Yes, because with its help you can create more compact and highly scalable memory chips, because here the floating gate transistor is isolated from the bit line. In addition, unlike a single-transistor memory cell, where information is written using the injection method of hot electrons, a two-transistor memory cell uses the Fowler-Nordheim quantum tunneling method to record and erase information. This approach makes it possible to reduce the voltage required for the write operation. Looking ahead, I will say that two-transistor cells are used in memory with a NAND structure.
Flash memory device with NOR architecture.
The type of this memory is the source and a kind of impetus in the development of the entire EEPROM. Its architecture was developed by Intel back in 1988. As was written earlier, in order to access the contents of a memory cell (initialize the cell), you need to apply voltage to the control gate.
Therefore, the company's developers connected all control gates to a control line called the Word Line. Analysis of memory cell information is performed based on the signal level at the drain of the transistor. Therefore, the developers connected all the drains of the transistors to a line called the Bit Line.
The NOR architecture got its name due to the logical operation OR - NOT (translated from English NOR). The principle of the logical operation NOR is that over several operands (data, argument of the operation...) it gives a unit value when all operands are equal to zero, and a zero value in all other operations.
In our case, operands mean the value of memory cells, which means that in this architecture, a single value on the bit line will be observed only if the value of all cells connected to the bit line is equal to zero (all transistors are closed).
This architecture has good random access to memory, but the process of writing and erasing data is relatively slow. The hot electron injection method is used in the writing and erasing process. In addition, the flash memory chip has a NOR architecture and its cell size is large, so this memory does not scale well.
Six Cell NOR Flash Structure Flash memory with NOR architecture is typically used in devices for storing program code. These could be phones, PDAs, motherboard BIOS...
Flash memory device with NAND architecture.
This type of memory was developed by Toshiba. Due to their architecture, these chips are used in small drives called NAND (logical NAND operation). When executed, the NAND operation produces a value of zero only when all operands are zero, and a value of one in all other cases.
As was written earlier, the zero value is the open state of the transistor. As a consequence, the NAND architecture assumes that a bitline has a value of zero when all transistors connected to it are open, and a value of one when at least one of the transistors is closed. Such an architecture can be built by connecting transistors with a bit line not one at a time (as built in the NOR architecture), but in serial series (a column of sequentially connected cells).
This architecture is highly scalable compared to NOR because it allows transistors to be compactly placed on the circuit. In addition, the NAND architecture writes using Fowler-Nordheim tunneling, and this allows for faster recording than in the NOR structure. To increase read speed, NAND chips have an internal cache built into them.
Like hard disk clusters, NAND cells are grouped into small blocks. For this reason, when reading or writing sequentially, NAND will have a speed advantage. But on the other hand, NAND loses greatly in random access operations and does not have the ability to work directly with bytes of information. In a situation where only a few bits need to be changed, the system is forced to rewrite the entire block, and this, taking into account the limited number of write cycles, leads to a lot of wear on the memory cells.
Single Column Structure of NAND Flash Recently, there have been rumors that Unity Semiconductor is developing a new generation of flash memory, which will be built on CMOx technology. It is assumed that the new memory will replace NAND flash memory and overcome its limitations, which in NAND memory are determined by the architecture of transistor structures. The advantages of CMOx include higher recording density and speed, as well as a more attractive cost. Application areas for the new memory include SSDs and mobile devices. Well, time will tell whether this is true or not.
In order to convey to you all the necessary information in more detail, I posted a video clip on the topic.
P.S. Explaining technical material in simple language to people who have no idea how computer architecture is built... is very difficult, but I hope I succeeded. For complete and reliable information in this article, I partially used educational literature. I hope this article was useful and informative for you. Bye!
Today, manufacturers produce several types of flash memory drives: these are cards Compact Flash, SmartMedia, MultiMedia Card, SecureDigital Card, Memory Stick and USB keys.
ATAFlash. The first flash memory drives to hit the market were cards ATA Flash . These drives are manufactured in the form of standard cards PC Card . In addition to flash memory chips, an ATA controller is installed in them, and during operation they emulate a regular IDE -disk. The interface of these cards is parallel. Cards ATA Flash are not widely used and are currently used extremely rarely.
CompactFlash. Compact Flash Cards (CF ) were offered by the company SanDisk as a more compact and easy-to-use alternative to cards ATA Flash . Therefore, the developers of the standard CF provided for the possibility of operating these cards as devices PC Card or as IDE -devices. In the first case, the cards work like regular ones PC Card devices and their interface “turns” into a bus PC Card . In the second - how tough IDE -disks and their interface works like an ATA bus.
CF Cards first appeared in 1994. All cards of this type have a 50-pin parallel interface. By the way, there are maps CF two types - Ture I and Tour II . Toure type cards II two millimeters thicker and appeared only because Toure card bodies preceded them I did not allow large-capacity flash memory to be placed inside for the production of capacious media CF . Currently there is no such need and the Toure card II gradually leaving the market. Please note that the drives for Tour cards II You can install Tour maps I , while the opposite is not possible.
Among flash cards, the undisputed leader in performance was Transcend Ultra Performance CF Card 25 x CompactFlash 256 MB, which can rightfully be considered the standard for the speed of modern flash drives. The sequential/random write speed of this flash card reaches 3.6/0.8 MB/s, the read speed is 4.0/3.7 MB/s.
CF operating speed -cards slow down with increasing volume, which is clearly seen in the example of flash cards512 MB. A twofold increase in capacity leads to a 30% decrease in productivity. with the exception of the random write speed, which has increased by 2.5 times - this looks rather strange and unexpected.
Speed characteristics CF -cards also greatly depend on the manufacturer. U Kingston CompactFlash 256 MB - low write speed (sequential/random write - 1.4/0.3 MB/s), but in terms of read speed it was the leader (4.4/3.8 MB/s). Map PQI Hi - Speed Compact Flash 256 MB demonstrated average performance in both cases: writing - 2.1/0.7 MB/s, reading - 3.8/3.3 MB/s. Cards SanDisk CompactFlash 256 MB and SanDisk CompactFlash 512 MB worked very slowly: writing - 1.1/0.2 and 0.9/0.5 MB/s, reading - 2.3/2.1 and 1.8/1.7 MB/s. And the map256 MB wrote and read data equally well.
If we compare CF cards with other types of drives, it turns out that flash memory is not at all as slow as is commonly believed! In terms of performance, the fastest flash memory samples (let's take the card as a standard Transcend Ultra Performance 25x CompactFlash 256 MB) are comparable to Iomega Zip 750 MB, and in terms of sequential write speed they even outpace this drive by more than 1.5 times! Flash memory outperforms disks in sequential write speed CD-RW 2 times, sequential reading speed - by 10%! Flash memory outperforms MO disks in sequential write speed - 2 times - and random read speed - by 10%, but lags behind in sequential read speed and random write speed - by 20%. Flash memory lags behind in sequential write speed DVD -disks (when “burning” in 4x mode) - 1.4 times.
Note that if CF - the card is used in a digital camera, then speed is primarily important for it consistent recording - the higher it is, the faster the camera will return to working condition after “capturing” the frame and “resetting” it to the flash card. However, the reading speed CF -cards in this case are also important, although not so critical - the faster the data is read, the faster the camera will work in the viewing mode of the footage.
SmartMedia . Card design SmartMedia (SM ) is extremely simple. On the map S.M. there is no built-in interface controller and, in fact, it is one or two flash memory chips “packed” in a plastic casing. Standard S.M. was developed by companies Toshiba and Samsung in 1995 Map Interface S.M. - parallel, 22-pin, but only eight lines are used for data transmission.
MultiMedia Card . Multi-Media Cards (MMC) ) have a 7-pin serial interface that can operate at frequencies up to 20 MHz. Inside the plastic case of the card there is a flash memory chip and an MMC interface controller. The MMC standard was proposed in 1997 by companies Hitachi, SanDisk and Siemens.
SecureDigital Card . SecureDigi-tal Card (SD ) is the youngest flash card standard: it was developed in 2000 by companies Matsushita, SanDisk and Toshiba. Actually SD - this is a further development of the MMC standard, so MMC cards can be installed in drives SD (the reverse will not be true). Interface SD - 9-pin, serial-parallel (data can be transmitted one at a time,two or four lines simultaneously), operates at frequencies up to 25 MHz. Cards SD are equipped with a switch to protect their contents from writing (the standard also provides for a modification without such a switch).
USB -flash memory. USB flash memory (USB -memory) is a completely new type of flash memory media that appeared on the market in 2001. By USB form - the memory resembles an oblong-shaped keychain, consisting of two halves - a protective cap and the drive itself with USB - connector (one or two flash memory chips are placed inside it and USB controller).
Work with USB -memory is very convenient - no additional devices are required. It is enough to have a PC at hand running Windows with unused USB -port to “get” to the contents of this drive in a couple of minutes. Worst case scenario you will have to install drivers USB -memory, at best - new USB -the device and logical drive will appear in the system automatically. It is possible that in the future USB -memory will become the main type of device for storing and transferring small amounts of data.
What about USB? -flash memory, then this is undoubtedly a more convenient solution for transferring data than flash cards - no additional flash drive is required. However, the performance of tested drives of this type is Transcend JetFlash 256 MB and Transcend JetFlashA 256 MB - limited by low interface bandwidth USB 1.1. Therefore, their performance in speed tests was rather modest. If USB -flash memory equipped with a fast interface USB 2.0, then in terms of “rate of fire” these drives, of course, will not be inferior to the best flash cards.
It is interesting to note that flash memory is superior in sequential write speed. Iomega Zip 750, CD - RW and MO carriers and is second only to DVD -disks. This once again emphasizes that flash memory developers primarily sought to increase speed consistent recording, since flash memory was originally intended for use in digital cameras, where this indicator is primarily important.
As a result, we can conclude that flash memory is the undisputed leader in reliability, mobility and power consumption among small and medium-capacity drives, which also has good performance and sufficient capacity (flash cards with a capacity of up to 2 GB are already available on the market today). Undoubtedly, this is a very promising type, but their widespread use is still limited by high prices.
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 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 BGA “chip” 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.
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 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 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.
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.
Flash memory is a type of solid-state semiconductor non-volatile rewritable memory.
Operating principle
Flash Memory Programming
Erasing flash memory
Story
Characteristics
File systems
Application
Types of memory cards
operator101 operator101
1
normal
Flash memory is a type of solid-state semiconductor non-volatile rewritable memory.
It can be read as many times as desired, but it can be written to such memory only a limited number of times (maximum - about a million cycles). Flash memory is common and can withstand about 100 thousand rewrite cycles - much more than a floppy disk or CD-RW can withstand.
It does not contain moving parts, so, unlike hard drives, it is more reliable and compact.
Due to its compactness, low cost and low power consumption, flash memory is widely used in portable devices that run on batteries and rechargeable batteries - digital cameras and camcorders, digital voice recorders, MP3 players, PDAs, mobile phones, as well as smartphones and communicators. In addition, it is used to store embedded software in various devices (routers, PBXs, printers, scanners), and various controllers.
Also recently, USB flash drives (flash drive, USB drive, USB disk) have become widespread, practically replacing floppy disks and CDs.
At the end of 2008, the main drawback that prevents flash memory-based devices from displacing hard drives from the market is the high price/volume ratio, which is 2-3 times higher than that of hard drives. In this regard, the volumes of flash drives are not so large. Although work in these directions is underway. The technological process becomes cheaper and competition intensifies. Many companies have already announced the release of SSD drives with a capacity of 256 GB or more.
Another disadvantage of flash memory-based devices compared to hard drives is, oddly enough, lower speed. Despite the fact that manufacturers of SSD drives assure that the speed of these devices is higher than the speed of hard drives, in reality it turns out to be significantly lower. Of course, an SSD drive does not spend time like a hard drive on overclocking, positioning heads, etc. But the reading, and even more so writing, time of flash memory cells used in modern SSD drives is longer. Which leads to a significant decrease in overall performance. To be fair, it should be noted that the latest models of SSD drives are already very close to hard drives in this parameter. However, these models are still too expensive.
In February 2009, deliveries of USB-flash drives with a capacity of 512Gb began. This model has already gone on sale in Moscow. The estimated cost of such a model for the end consumer is planned to be around $250, which makes such a flash drive a clear competitor to external HDDs. The flash drive has a small compact size, a USB 2.0 interface, and a read speed of 11MB/sec. and 10MB/sec. for recording.Contents [remove]
Operating principle
Flash Memory Programming
Erasing flash memory
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) devices can store more than one bit by using different levels of electrical charge on a transistor's floating gate.
This type of flash memory is based on a NOR element because in a floating gate transistor, a low voltage at the gate 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 tunneling effect occurs. Some electrons tunnel through the insulator layer and end up on the floating gate, where they will remain. 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 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.
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 provide an individual contact to each cell, so the size and cost of the NAND chip can be significantly reduced. Also, recording 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.
Story
Flash memory was invented by Fujio Masuoka while he was working at Toshiba in 1984. The name "flash" was also coined at Toshiba by Fuji's colleague, Shoji Ariizumi, because the process of erasing the contents of memory reminded him of a flash. Masuoka presented his design at the IEEE 1984 International Electron Devices Meeting (IEDM), held in San Francisco, California. Intel saw great potential in the invention and released the first commercial NOR flash chip in 1988.
NAND flash memory was announced by Toshiba in 1989 at the International Solid-State Circuits Conference. It had a faster write speed and a smaller chip area.
At the end of 2008, the leaders in flash memory production are Samsung (31% of the market) and Toshiba (19% of the market, including joint factories with Sandisk). (Data according to iSupply as of Q4"2008). The standardization of NAND flash memory chips is carried out by the Open NAND Flash Interface Working Group (ONFI). The current standard is the ONFI specification version 1.0, released on December 28, 2006. The ONFI group is supported by competitors Samsung and Toshiba in NAND chip production: Intel, Hynix and Micron Technology.
Characteristics
Some devices with flash memory can reach speeds of up to 100 MB/s. In general, flash cards have a wide range of speeds and are usually labeled at the speeds of a standard CD drive (150 Kb/s). So the indicated speed of 100x means 100 H 150 Kb/s = 15,000 Kb/s = 14.65 Mb/s.
Basically, the volume of a flash memory chip is measured from kilobytes to several gigabytes.
In 2005, Toshiba and SanDisk introduced 1GB NAND chips using multi-level cell technology, where a single transistor can store multiple bits using varying levels of electrical charge on a floating gate.
In September 2006, Samsung introduced an 8 GB chip made using a 40 nm process technology. At the end of 2007, Samsung announced the creation of the world's first MLC (multi-level cell) NAND flash memory chip, made using a 30 nm process technology. The chip capacity is also 8 GB. Memory chips are expected to go into mass production in 2009.
To increase the volume, devices often use an array of several chips. Basically, as of mid-2007, USB devices and memory cards have a capacity of 512 MB to 64 GB. The largest capacity of USB devices is 1 TB.
File systems
The main weak point of flash memory is the number of rewrite cycles. The situation is also made worse by the fact that the OS frequently writes data to the same location. For example, the file system table is updated frequently, so the first sectors of memory will use up their supply much earlier. Load distribution can significantly extend the life of memory.
To solve this problem, special file systems were created: JFFS2 and YAFFS for GNU/Linux and exFAT for Microsoft Windows.
USB flash drives and memory cards, such as SecureDigital and CompactFlash, have a built-in controller that detects and corrects errors and tries to evenly use the flash memory rewrite resource. On such devices it makes no sense to use a special file system and for better compatibility, regular FAT is used.
Application
Flash cards of different types (match shown for size estimation)
Flash memory is best known for its use in USB flash drives. The main type of memory used is NAND, which is connected via USB via the USB mass storage device (USB MSC) interface. This interface is supported by all modern operating systems.
Thanks to their high speed, capacity and compact size, USB flash drives have completely replaced floppy disks from the market. For example, Dell stopped producing computers with a floppy drive in 2003.
Currently, a wide range of USB flash drives are produced in different shapes and colors. There are flash drives on the market with automatic encryption of the data recorded on them. The Japanese company Solid Alliance even produces flash drives in the form of food.
There are special GNU/Linux distributions and versions of programs that can work directly from USB drives, for example, to use your applications in an Internet cafe.
ReadyBoost technology in Windows Vista can use a USB flash drive or special flash memory built into the computer to increase performance. Flash memory is also the basis for memory cards, such as SecureDigital (SD) and Memory Stick, which are actively used in portable equipment (cameras, mobile phones). Together with USB storage devices, flash memory occupies the majority of the portable storage media market.
NOR type of memory is more often used in BIOS and ROM memory of devices, such as DSL modems, routers, etc. Flash memory allows you to easily update the firmware of devices, while the writing speed and capacity are not so important for such devices.
The possibility of replacing hard drives with flash memory is now being actively considered. As a result, the speed of turning on the computer will increase, and the absence of moving parts will increase the service life. For example, the XO-1, a “$100 laptop” that is being actively developed for third world countries, will use 1 GB of flash memory instead of a hard drive. Distribution is limited by the high price per GB and shorter shelf life than hard drives due to the limited number of write cycles.
Types of memory cards
There are several types of memory cards used in cell phones.
MMC (MultiMedia Card): a card in MMC format is small in size - 24x32x1.4 mm. Developed jointly by SanDisk and Siemens. The MMC contains a memory controller and is highly compatible with a wide variety of devices. In most cases, MMC cards are supported by devices with an SD slot.
RS-MMC (Reduced Size MultiMedia Card): A memory card that is half the length of a standard MMC card. Its dimensions are 24x18x1.4 mm, and its weight is about 6 g; all other characteristics do not differ from the MMC. To ensure compatibility with the MMC standard when using RS-MMC cards, an adapter is required.
DV-RS-MMC (Dual Voltage Reduced Size MultiMedia Card): DV-RS-MMC memory cards with dual power (1.8 and 3.3 V) feature reduced power consumption, which will allow your mobile phone to work a little longer. The card dimensions are the same as RS-MMC, 24x18x1.4 mm.
MMCmicro: miniature memory card for mobile devices with dimensions 14x12x1.1 mm. To ensure compatibility with a standard MMC slot, an adapter must be used.
SD Card (Secure Digital Card): Supported by SanDisk, Panasonic and Toshiba. The SD standard is a further development of the MMC standard. In terms of size and characteristics, SD cards are very similar to MMC, only slightly thicker (32x24x2.1 mm). The main difference from MMC is copyright protection technology: the card has cryptographic protection against unauthorized copying, increased protection of information from accidental erasure or destruction, and a mechanical write-protect switch. Despite the similarity of the standards, SD cards cannot be used in devices with an MMC slot.
SD (Trans-Flash) and SDHC (High Capacity): Old SD cards so-called. Trans-Flash and new SDHC (High Capacity) and their reading devices differ in the limitation on the maximum storage capacity, 2GB for Trans-Flash and 32GB for High Capacity. SDHC readers are backward compatible with SDTF, that is, an SDTF card will be read without problems in an SDHC reader, but in an SDTF device only 2GB of the larger SDHC capacity will be seen, or will not be read at all. It is assumed that the TransFlash format will be completely replaced by the SDHC format. Both sub-formats can be presented in any of the three physical formats. sizes (Standard, mini and micro).
miniSD (Mini Secure Digital Card): They differ from standard Secure Digital cards in their smaller dimensions of 21.5x20x1.4 mm. To ensure the card works in devices equipped with a regular SD slot, an adapter is used.
microSD (Micro Secure Digital Card): are currently (2008) the most compact removable flash memory devices (11x15x1 mm). They are used primarily in mobile phones, communicators, etc., since, due to their compactness, they can significantly expand the memory of the device without increasing its size. The write protection switch is located on the microSD-SD adapter.
MS Duo (Memory Stick Duo): This memory standard was developed and supported by Sony. The case is quite durable. At the moment, this is the most expensive memory of all presented. Memory Stick Duo was developed on the basis of the widely used Memory Stick standard from the same Sony, and is distinguished by its small dimensions (20x31x1.6 mm).