What is flash memory in a computer

In the everyday life of users, a new word has appeared – “flash drive”. Most people know for sure that this device is used in digital cameras, and is also designed to transfer videos and music. But this is not a complete list of functions that the 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.

Plunging into 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, which presented its 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 vaguely resembles a photo flash.

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

Not all memory is flash

Diving deep into the world of physics, you can learn that there are several types of memory.

Random access memory, which works on the principle of “electrical capacity”. 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 irrevocably.
Permanent memory. Information on the medium is stored by physical or chemical action. An example is an optical DVD, information on which is recorded by burning microscopic holes on the surface of plastic with a laser.
Conditional non-volatile memory. This includes flash memory, magnetic hard disks, floppy disks, videotape and other media that can hold a magnetic or electrical charge in the absence of a constant source of electricity.

Flash memory applications

For 20th century technology, devices such as memory sticks and USB flash drives were sufficient for the invention. But in the 21st century there has been a boom in storage media with flash technology. First of all, all mobile phones, tablets, multimedia players and digital devices have 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. Get at least a flashlight for a police officer. Thanks to the presence of flash memory in it, the human rights activist can choose the focus and beam brightness he needs from the saved settings.

How many device manufacturers

On the market, you can see that the required flash memory is provided by several manufacturers at once. Having almost the same characteristics, the drives differ significantly in price. Is the most expensive purchase the best? Not always! Often the buyer has to pay extra 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 already in their own name. The only difference is the speed of the devices, depending on the capabilities of the flash memory. Whether the memory is fast or not, it is up to the manufacturer to decide.

About prices for flash devices

Anyone who has decided to purchase a flash memory on their own may find the prices on the market 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 make markings on the body of the product. Often in the store you can find devices on which there is no marking, there is only the logo of the manufacturer. Prices for such memory cards are very low, and the seller claims high performance in the device. Reviews of experts on the pages of respected computer publications recommend refraining from buying unmarked devices, since they are fake or imported into the country illegally.

What you need to know about flash drive labels

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

The name of the manufacturing company or its logo must be present.
The amount of flash memory must be written on the medium.
The class of the flash device must be indicated on the case. Often manufacturers of USB modules indicate the class on the packaging of the goods, which is not prohibited by law.

On sale you can find flash memory cards without marking, but with a long number, which is stuffed in small print on the body of the device. 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?

Zero class. Recording speed is not less than 0.6 MB per second. In stores, you can buy without seeing the lack of labeling. Suitable for storing documentation.
Classes 2 and 4, with write speeds of 2 and 4 MB per second, respectively, also belong to the office section and are intended for storing and transferring documentation.
The sixth and eighth grades at 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 applications.
Grade ten and above, including Ultra, show write speeds in excess of 10MB per second. They are used in work with multimedia, as additional drives for workstations, used as random access memory. Where the speed of reading and writing to a storage medium is critical.

Serious brands such as Pretec and Corsair make high-speed devices with the ability to write up to 25MB per second, labeling them as 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. Even if technology does not stand still, there are still some limits. When it is necessary to change the technical process to increase the amount of memory, a dilemma arises – keeping the price low, staying on the achieved result or developing further, looking for wealthy buyers. There has been some lull in the world – buyers are offered to buy memory cards with a maximum capacity of 64 gigabytes, if you want to, you can become the owner of 128 GB and 256 GB, 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 quite 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 writing, 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 mistake by the manufacturer – and the device can end up in the trash can. It’s complicated, expensive and very serious, but the future belongs to the SSD. Direct competitor to computer hard drives that operate by magnetism. Resistant to shocks, temperatures and works silently. The day is not far off when magnetic hard drives will share space in a ball mouse cabinet, giving way to 21st century technology.

How to save money on improving your computer

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 is to buy a modern computer. After 5 years, the same specialist will come and will once again prove 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.

See also: What are backing tracks

RAM 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 give preference to

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.

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

Having found several required options, ask the seller how issues are resolved in the event of a device breakdown, whether there is a warranty replacement. Flash memory is a consumable and cannot be repaired – you need to know about this before buying. The manufacturers Corsair, Kingston, OCZ, Pretec, Silicon Power, Transcend and IBM deserve positive reviews.

How to protect yourself from losing information from a flash drive

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

Physical breakdown of modules. It is very easy to break plastic flash cards, but it is impossible to restore, therefore, when buying, you need to pay attention to metal flash drives or use them very carefully.
Moisture can destroy the drive. It is worth paying attention to waterproof media if there is a possibility of water getting into memory.
Infection of flash memory with viruses. Sometimes it turns out to be 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.

Conclusion and recommendations

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

Experts recommend giving preference to proven 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. It is worth visiting to get an idea of the company.
You should not trust your choice to 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 work of the carrier before buying. The usual formatting of the device in the Windows environment allows you to determine the health of the flash memory.
Preference should be given to fast devices that are of the tenth grade. Since there are often situations when time is a priority. Then the flash memory will become universal for the user for any device.
When buying memory cards for digital technology, it is worth worrying about the possibilities of reading data on a computer. For this, there are all kinds of adapters, which are often offered for purchase along with flash memory.

Flash memory stores information in an array of floating gate transistors, called cells (Engl. Cell ). In traditional devices with single-level cells (English single-level cells, SLC ), each of them can store only one bit. Some newer multi-level cells (MLCs ) can store more than one bit using different levels of electrical charge across the floating gate of the transistor.

At the heart of this type of flash memory is an OR-NOT element (English NOR ), because in a floating gate transistor, a low gate voltage denotes one.

The transistor has two gates: control and floating. The latter is completely isolated and can hold electrons for up to 10 years. The cell also contains 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 land on the floating gate, where they will stay. The floating gate charge changes the “width” of the drain-source channel and its conductivity, which is used for reading.

Programming and reading cells differ greatly in power consumption: flash memory devices consume a fairly large current when writing, while when reading, the power consumption is low.

To erase information, a high negative voltage is applied to the control gate, and electrons from the floating gate pass (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 the NAND architecture.

At the core lies a NAND and NOR element (Eng. NAND ). The principle of operation is the same, it differs from the NOR type only in the placement of cells and their contacts. As a result, it is no longer necessary to bring an individual contact to each cell, so the size and cost of the NAND chip can be significantly less. 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.

History

Flash memory was invented by Fujio Masuoka when he was working in 1984. The name “flash” was also coined in Toshiba by Fuji’s colleague Shoji Ariizumi, because the process of erasing the contents of memory reminded him of a flash . Masuoka presented his development at the IEEE 1984 International Electron Devices Meeting (IEDM) held in San Francisco, California. 1988 released the first commercial NOR flash chip.

The NAND type of flash memory was announced by Toshiba in 1989 at the International Solid-State Circuits Conference. It had a higher write speed and a smaller chip area.

At the end of 2008, the leaders in the production of flash memory 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). NAND flash memory chips are standardized by the Open NAND Flash Interface Working Group (ONFI). The current standard is ONFI specification version 1.0 [2], released on December 28, 2006. The ONFI group is supported by competitors Samsung and Toshiba in the production of NAND chips: Hynix and Micron Technology. [3]

Specifications

Some devices with flash memory can reach speeds of up to 100 Mb / s [4]. 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 specified speed of 100x means 100 × 150 KB / s = 15,000 KB / s = 14.65 MB / s.

Basically, the size of a flash memory chip is measured from kilobytes to several gigabytes.

In 2005, SanDisk introduced 1 GB NAND chips [5], made using multilevel cell technology, where one transistor can store several bits using different levels of electrical charge on the floating gate.

Samsung in September 2006 presented an 8 GB chip, made according to a 40 nm technological process [6]. 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 30nm process technology. The capacity of the chip is also 8 GB. The memory chips are expected to enter mass production in 2009.

To increase the volume, devices often use an array of several chips. By 2007, USB devices and memory sticks ranged in size from 512 MB to 64 GB. The largest volume of USB devices was 4 TB.

File systems

The main weak point of flash memory is the number of rewriting cycles. The situation is also made worse by the fact that the OS often writes data to the same location. For example, the file system table is frequently updated so that the first memory sectors will use up much earlier. Load balancing can significantly extend the life of the memory.

To solve this problem, special file systems were created: JFFS2 [7] and YAFFS [8] for GNU / Linux and Microsoft Windows.

SecureDigital and FAT.

Application

Flash memory is best known for its use in USB flash drives . Basically, NAND type of memory is used, which is connected via USB via the USB mass storage device (USB MSC) interface. This interface is supported by all modern OS versions.

Due to its high speed, volume and compact size, USB flash drives have completely replaced floppy disks from the market. For example, a company in 2003 stopped producing computers with a floppy disk drive [9].

At the moment, a wide range of USB flash drives is produced, in different shapes and colors. There are flash drives on the market with automatic encryption of the data written to them. Japanese company Sol> [10].

There are special GNU / Linux distributions and versions of programs that can work directly from USB drives, for example, to use their applications in an Internet cafe.

See also: Digital set-top box to the monitor for watching TV

Windows Vista technology is capable of using a USB flash drive or special flash memory built into a computer to increase performance [11]. Flash memory is also based on memory cards such as SecureDigital (SD) and Memory Stick, which are actively used in portable technology (cameras, mobile phones). Together with USB drives, flash memory occupies a large part of the portable data storage 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 write speed and volume are not so important for such devices.

The possibility of replacing hard drives with flash memory is actively being 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 actively being developed for third world countries, will use 1 GB flash memory instead of a hard drive [12]. Distribution is limited by the high cost 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 portable devices:

MMC (MultiMedia Card) : A card in MMC format has a small size of 24 × 32 × 1.4 mm. Developed jointly by SanDisk and Siemens. MMC contains a memory controller and is highly compatible with various types 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 size of a standard MMC card. Its dimensions are 24 × 18 × 1.4 mm, and its weight is about 6 g, all other characteristics do not differ from MMC. An adapter is required to ensure compatibility with the MMC standard when using RS-MMC cards. DV-RS-MMC (Dual Voltage Reduced Size MultiMedia Card) : DV-RS-MMC memory cards with dual power (1.8V and 3.3V) feature lower power consumption, allowing your mobile phone to last a little longer. The card has the same dimensions as RS-MMC, 24 × 18 × 1.4 mm. MMCmicro : miniature memory card for mobile devices with dimensions of 14 x 12 x 1.1 mm. To ensure compatibility with a standard MMC slot, an adapter must be used.

SD Card (Secure Digital Card) : Supported by Panasonic and SD (Trans-Flash) and SDHC (High Capacity) : Old so-called Trans-Flash SD cards and newer SDHC (High Capacity) cards and their readers differ in the maximum storage capacity limit , 2 GB for Trans-Flash and 32 GB 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 an SDTF device will only see 2 GB of the larger SDHC capacity, or it 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): It differs from standard Secure Digital cards in smaller dimensions of 21.5 × 20 × 1.4 mm. To ensure the operation of the card 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 (11 × 15 × 1 mm). They are used primarily in mobile phones, communicators, etc., since, due to their compactness, they can significantly expand the device’s memory without increasing its size. The write-protect switch is located on the microSD-SD adapter.

MS Duo (Memory Stick Duo) : This memory standard was developed and supported by MS Duo (Memory Stick Duo) : This format competes with the microSD format (in the same size), while retaining the advantages of Sony memory cards.

xD-Picture Card : Used in digital cameras from Fuji and some others.

In this article, we will talk with you about what is the basis of creation and how 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 (permanent storage 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 need 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 semiconductors of electrically programmable memory (EEPROM). Due to technical solutions, low cost, large volume, low power consumption, high speed of operation, compactness and mechanical strength, flash memory is embedded in digital portable devices and storage media.

Flash memory has both its advantages and disadvantages over other drives (hard drives and optical drives) such as ROM, which you can see from the table below.

ROM type	Advantages	disadvantages
HDD	Large amount of stored information.

High speed of work.

The cheapness of data storage (per 1 MB).

Vibration sensitivity.

Optical disc Convenient transportation.

The cheapness of information storage.

You need a reader.

Restrictions on operations (read, write).

Low speed of work.

Vibration sensitivity.

Flash memory High speed data access.

Vibration resistance.

Convenience of connecting to a computer.

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 USB flash drives and removable memory cards for electronic devices (SD, MMC, miniSD …) work on the basis of flash memory.

Memory cards, like USB drives, do not stand aside, but attract the attention of potential buyers with their diversity. Only the manufacturer benefits from such an abundance of storage devices, and the consumer experiences a number of inconveniences. After all, we are all familiar with situations when a phone needs one card, a PDA another, a camera a third. Such an assortment of drives is in the hands of manufacturers, because they benefit from a wide exclusive sale. Here is a small list of common flash drives:

Compact Flash Type I (CF I) / Type II (CF II);
Memory Styck (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 USB flash drive, and how to choose a card in SD format (microSD, miniSD) read here.

How flash memory works.

The flash memory unit cell is a floating gate transistor. The peculiarity of such a transistor is that it can hold electrons (charge). It is on its basis that the main types of NAND and NOR flash memory are developed . There is no competition between them, because each of the types has its own advantages and disadvantages. By the way, hybrid versions such as DiNOR and superAND are built on their basis .

In flash memory, manufacturers use two types of memory cells, MLC and SLC.

Flash memory with MLC (Multi-level cells) cells are more capacious and cheaper, but they have a longer access time and fewer write / erase cycles (about 10,000).
Flash memory, which contains SLC (Single-level cells) cells, has a maximum number of write / erase cycles (100,000) and has a shorter access time.

The change in charge (write / erase) is performed by applying a large potential between the gate and the source so that the electric field in the thin dielectric between the channel of the transistor and the pocket is sufficient for the tunneling effect to occur. To enhance the effect of electron tunneling into the pocket during recording, a slight acceleration of electrons is applied by passing a current through the channel of the field-effect transistor.

The principle of operation of flash memory is based on the change and registration of an electric charge in an isolated area (“pocket”) of a semiconductor structure.

Reading is performed by a field-effect transistor, for which the pocket acts as a gate. The potential of the floating gate changes the threshold characteristics of the transistor, which is recorded by the read circuits. This design is supplied 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 (initialization of the memory cell), then it will be in the open state, which will correspond to a logical zero.

And if an excess negative charge (electron) is placed on the floating gate and a positive voltage is applied to the control gate, then it compensates the electric field created by the control gate and will not allow the conduction channel to form, which means that the transistor will be in a closed state.

See also: How to add your photos to saved photos

So, the presence or absence of charge on the floating gate accurately determines the state of the open or closed transistor when the same positive voltage is applied to the control gate. If we consider the supply of voltage to the control gate as the initialization of 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.

Thus, 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 any) can be stored there for a long time, both when the memory cell is initialized and in the absence of voltage at the control gate. Only in this case the memory cell will be non-volatile.

So how, if necessary, put a charge on the floating gate (write the contents of the memory cell) and remove it from there (erase the contents of the memory cell) when necessary.

The charge can be placed on the floating gate (recording process) by hot electron injection (CHE-Channel Hot Electrons) or by the Fowler-Nordheim tunneling method.

If the method of injection of hot electrons is used, then a high voltage is applied to the drain and the control gate, which will give the electrons in the channel enough energy to overcome the potential barrier, which is created by a thin dielectric layer, and direct (tunnel) into the floating gate region (during reading on a lower voltage is applied to the control gate and the tunneling effect does not occur).

To remove the charge from the floating gate (erase the memory cell), a high negative voltage (about 9 V) is applied to the control gate, and a positive voltage is applied to the source region. This leads to the fact that electrons tunnel from the area of the floating gate to the area of the source. This is how the Fowler-Nordheim quantum tunneling occurs.

You’ve probably figured out by now that a floating gate transistor is an elementary 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 the bus called the Bit Line. As a result, there is a high voltage in the circuit and when recording by injection of hot electrons, all lines – words, bits and sources – must be placed at a great distance from each other. This will provide the desired level of isolation, but will have an impact on limiting the amount of flash memory.

Another disadvantage of such a memory cell is the presence of the effect of excessive charge removal from the floating gate, which cannot be compensated for 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 cell that contains a conventional CMOS transistor and a floating gate transistor. In this structure, the conventional transistor acts as an insulator of the floating gate transistor from the bit line.

Does a two-transistor memory cell have any advantages? Yes, because it can be used to 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 by the injection of hot electrons, the Fowler-Nordheim quantum tunneling method is used to write and erase information in a two-transistor memory cell. 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 it was written earlier, in order to access the contents of the memory cell (initialize the cell), you need to apply voltage to the control gate.

Therefore, the developers of the company connected all the control gates to the control line, which is called the Word Line. The analysis of the information of the memory cell is performed according to 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, operation argument …) it gives a single 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 that are connected to the bit line are zero (all transistors are closed).

Random access to memory is well organized in this architecture, but the process of writing and erasing data is relatively slow. In the process of writing and erasing, the method of injection of hot electrons is applied. In addition, the NOR-based flash memory microcircuit and the size of its cell turn out to be large, so this memory does not scale well.

Structure of six cells NOR Flash

Flash memory with NOR architecture is usually used in devices for storing program code. These can be phones, PDAs, BIOS of motherboards …

NAND flash memory device.

This type of memory was developed by Toshiba. Due to their architecture, these microcircuits are used in small drives, which are named NAND (logical NAND operation). When executed, a NAND operation gives a value of zero only when all operands are zero, and one value in all other cases.

As it was written earlier, the zero value is the open state of the transistor. As a consequence, in the NAND architecture, it is assumed that the bit line has a zero value when all the transistors connected to it are on, and the value is one when at least one of the transistors is off. Such an architecture can be built by connecting the bitline transistors not one at a time (as built in the NOR architecture), but in series (a column of cells connected in series).

This architecture, in comparison with NOR, is well scalable because it allows you to compactly place transistors on the circuit. In addition, the NAND architecture writes by means of Fowler-Nordheim tunneling, and this allows for faster writing than in the NOR structure. To increase read speed, NAND chips build in an internal cache.

Like hard disk clusters, NAND cells are grouped into small blocks. For this reason, when reading or writing sequentially, NAND will have the speed advantage. But on the other hand, NAND loses a lot 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, given the limited number of write cycles, leads to a lot of wear and tear on memory cells.

NAND Flash Single Column Structure

There have been rumors lately that Unity Semiconductor is developing next-generation flash memory that will be built on CMOx technology. It is expected that the new memory will replace NAND flash memory and overcome its limitations, which in NAND memory are caused by the architecture of transistor structures. The advantages of CMOx include higher density and write speed, as well as more attractive cost. Applications for the new memory include SSDs and mobile devices. Well, what is true or not, time will tell.

In order to convey to you all the necessary information in more detail, I posted a video clip on the topic.

PS To explain technical material in simple language to people who have no idea how the architecture of a computer is built … it’s 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!