Almost every person who works at a computer knows about the existence of a device called a “flash drive” (USB drive). Initially, these drives were quite expensive and were considered exotic devices. Back then they were not very common, and people exchanged information using disks, hard drives and floppy disks. Today, these drives have almost completely replaced the above methods of information transfer.
A USB drive is an electronic device that is used as a storage and storage medium. It connects to a personal computer, laptop, etc. The main advantages of this device are ease of use, a wide range of models and a fairly low price. Among its main characteristics are compactness, a significant amount of memory, and high data transfer speed. The drive is a universal device and is perfectly protected from mechanical influences. You can easily carry it in your pocket and use it if necessary.
Kinds
A flash drive can be completely different in its design. You can buy a wide variety of drives in stores, which will differ in capacity, design, interface type and capabilities.
- In terms of memory capacity, drives can reach 1 terabyte, that is, 1024 Gb. However, today devices with a capacity of 4-32 Gb are most widespread. Their cost varies between 150-3000 rubles. The multiple of memory capacity corresponds to 2, that is, 32, 64, 128 Gb. Devices up to 4GB are great for storing and moving text files. For storing music, photos or small videos, a 16 GB drive is sufficient. A 32 Gb device is well suited for video storage.
- According to USB interface standards, drives can be of the following types:
USB 1.0;
1.1;
2.0;
3.0;
3.1.
The main distinguishing feature of these types of drives is the data transfer speed. So USB 1.1 transmits data at a speed of 600-800 KB per second. In this case, recording is supported up to 700 KB per second. USB 2.0 more advanced, they can transmit data at a speed of 480 Mbit per second. USB 3.0 introduces a new type of drive that allows data transfer at speeds of up to 5 Gbit per second. Standard devices USB 3.1 capable of transmitting data at speeds up to 10-12 Gbit per second.
However, do not delude yourself with the desire to own the most advanced device. Actually a drive USB 3.1 unlikely to support most of your devices. The fact is that the USB receivers themselves in most cases have standard devices installed. USB 2.0. As a result, when connected to a USB 2.0 port or in reverse order, the drive will operate in information transfer mode USB 2.0, that is, the speed will be significantly limited.
- Today you can buy an incredible number of drives of various designs, which are made of different materials. It can be plastic, wood, glass, silicone, leather, metal, rubber and so on. Various drawings, engravings and other design elements can be applied to the drive body. However, the use of one or another design effect does not in any way affect the technical indicators in the form of speed and volume of data transfer.
- Availability of additional functions. For example, a flash drive may have a code input device. Therefore, to start working with it, you will need to enter the correct code. This helps protect against data theft. There may also be drives with a fingerprint scanner. In this case, to be able to work with the device, you will have to place your finger on the scanner, which is located on the case.
There may also be drives that operate using voice control. Such a device recognizes the owner’s voice, after which it unlocks the ability to work with data. There are devices with antibacterial coating. The body of such a drive is made using special antibacterial materials, so that germs do not multiply on it.
There are also double-sided drives. The flash drive has two USB connectors. Using such a drive, you can store work information and personal information separately. This is convenient in cases where you might accidentally overwrite an important document. Devices are sold that combine a storage device and a digital camera.
Device
In most cases, a flash drive consists of the following main elements:
The USB connector allows you to connect to a computer or other electronic device. With the help of a stabilizer, the voltage is converted and stabilized, which comes from the PC directly to the controller and flash memory.
The controller represents the circuitry that controls memory as well as data transfer. It has a chip that contains all the information about the memory, manufacturer. It also stores service information that is required for normal operation of the drive. In some models, the controller may be built-in or absent altogether.
Using a quartz resonator, the reference frequency of flash memory and controller logic is created. The case serves to protect against mechanical damage and accommodate all elements of the drive. The switch is required to enable write or write protection mode. An LED that blinks shows the user that the drive is working. At this time, it is highly recommended not to remove the drive from the USB connector. This can lead to data loss and even device failure.
Application
A flash drive is a universal device on which you can store any information, rewrite, erase and transfer it. You can record text documents, photos, videos, music on the drive, and you can also read, erase and edit information on it. The peculiarity of the drive is that it can be connected an infinite number of times.
The device can even be connected while the computer is running. The device case helps to protect all elements of the device well. Thanks to this, the drive is practically not afraid of falling, prolonged wearing in trouser pockets and other mechanical influences. The drive does not need an external power source, because the electricity supplied to it via the USB port is sufficient for it.
How to choose
A flash drive is a fairly simple device, but you also need to choose it wisely.
- To select a suitable device, you must first take a closer look at the amount of memory, appearance and data transfer speed.
- At this point in time, the best option is a drive with a memory capacity of 32 GB or higher. This is due to the fact that the cost of such devices is low, but this amount of memory is quite enough to record several high-quality films, a huge number of Word documents or pictures.
- You shouldn’t save a lot and buy a little-known media brand without a name. So you can run into a Chinese craft. In addition, the difference in price between branded and “unknown” media will be insignificant. Therefore, if you don’t know which brand to choose, then take a closer look at manufacturers such as Transcend, silicon-power, San Disk, Kingston and so on.
- It is not recommended to purchase a drive with a retractable connector. Many models have a connector that slides out rather than being hidden behind a cap. On the one hand, it looks beautiful and convenient, but in practice everything happens a little differently. This device is quite fragile and unreliable. If you apply force, the drive may break, which will require you to purchase a new device.
- When purchasing a drive, take a closer look at its design. Quite often they are made in the form of pendants or keychains, which allows you to use the drive not only as a useful device, but also as a rather fashionable accessory. Paying attention to the size, it is desirable that the flash drive takes up minimal space. At the same time, excessively miniature devices are very fragile. Therefore, decide for yourself what is more important to you: beauty or reliability.
- If you want to protect the data on the drive from unauthorized persons, then you need to buy devices with additional security features. For example, this could be protection in the form of a special program on a flash drive that will ask for a password, or a device with a fingerprint scanner.
You can read about what a flash drive is on many sites. They will also tell you in detail what not to do with it. But how do you know what you can do with it? How about a lesson with a visual demonstration of all points (from A to Z) about working with a flash drive? Let's say that you wish to transfer text from one computer to another (even if the second computer is not connected to the Internet).
And in the second case, a cartoon, in the third case, both. What is most important in the lesson is ALL the sequential transfer actions.
Original requirement? But this is the only way to show, explain, and protect dunno (a pebble in the garden of beginners who cannot handle it with a flash drive) from unnecessary and unnecessary actions!
There is a lot of information about a flash drive, but there are no specific step-by-step “instructions” for working with a flash drive! But in vain! I am sure that many people have such “difficulties”, but I should write about them. So here's a lesson on working with a flash drive.
This is what a regular flash drive looks like.
Step 1. You insert it intoUSB port(see picture).
Next to this port are usually headphone and microphone jacks.
Here they are, green and pink side by side.
Step 2. Now click “Start”. Then "My Computer". Among the pictures you will see a picture of a removable disk. It can have any name.
The main thing is its visual representation in the picture.
For example, "KINGSTON (F:)". In this case, “KINGSTON” means the name of the flash drive manufacturer, and (F:) is the name of the disk.
Step 3. Write information to a flash drive it is possible in at least 2 ways. Let's look at both.
1 way. Let's continue from where we left off.
1. Click on the image of the flash drive with the left mouse button. As a result, its contents will be revealed to you.
2. Select the desired file (text document, music, video, whatever) that you want to copy to the flash drive on your desktop or in any other folder.
3. Now grab it with the left mouse button and drag it to the flash drive folder. You let go.
All. You copied the file to the flash drive!
2. method.
1.Select the file you need to copy to the flash drive.
2. Click on it with the right mouse button.
3. Select “Send”
4. Then select the item with the image of the flash drive. In our example, “KINGSTON (F:)”.
5. That's it, the file has been sent to the flash drive. You can check its presence on the flash drive.
Step 4. The information you have recorded . Now you need to safely remove the flash drive from the computer. To do this, do the following.
That's all. Now you have mastered working with a flash drive. And we are ready to conquer new computer horizons! Good luck with this!
Currently, a portable storage device will not surprise any user with its functionality. However, at one time, the flash drive made a truly technological revolution in the field of data storage devices. This device replaced floppy compact discs, as well as floppy disks, gradually displacing them from the market.
In this material we will look at the design of a flash drive, the principle of operation and connecting it to a personal computer or to another device capable of reading information from a portable drive. Let's figure out how to restore a non-working flash drive, as well as remove write protection.
General information about the portable flash device
The USB flash drive was invented by Israeli scientists working for M-Systems in 1999. But the device itself was patented in the United States of America, also in 1999. The first presentation of the flash drive took place in 2000, where it received its original name DiskOnKey (disk on a key). The volume of the first portable drive was 8 megabytes, but soon devices with 16 and 32 MB appeared.
At that time, a flash drive could be called a full-fledged gadget; it was sold for a considerable price of $50, which increased by the end of the year with the advent of larger drives to $100 per piece. The sale was led by IBM.
Currently, flash drives have almost completely replaced outdated CDs from the portable device market. There are now two terabyte drives from manufacturers such as HyperX and Kingston. Just imagine the size of one and a half matchboxes, on which two terabytes of disk space are located. How does a two terabyte flash drive work? Just like a flash drive with 16 gigabytes, everything is very simple and very effective.
Advantages and disadvantages of USB storage
Since these devices are indispensable portable storage media today, it is worth understanding their advantages and potential disadvantages. After all, it is these two parameters that accompany progress in various technologies and the development of new devices. Indispensability means monopoly in any device market. So, let's find out why and in the process indirectly get acquainted with how a flash drive works.
Advantages:
- Portability and light weight of the device.
- Quiet operation and low resource consumption.
- Low energy consumption (primarily due to the absence of mechanical systems).
- Possibility of operation at high temperatures.
- Resistant to mechanical stress (unlike hard drives and CDs).
- Protected from environmental influences (scratches, dust, damage from drying out).
- Long-term data storage time offline is, at best, 10 years or more, at worst, with a low-quality device, from 3 to 6 months.
Flaws:
- Limited number of times data can be written and erased before failure. About 5000 rewrite cycles.
- The limited number of USB connector connections is about 1500 times.
- Limited recording speed, which is quite noticeable for a USB 2.0 port (no more than 35 megabytes per second).
- Sensitive to electrical short circuits and radiation, just like any other electronics.
- The disadvantage is the shape of the connector and the connected drive, which increases wear on the port and connector. This problem was solved with the USB Type-C output.
Thus, from the above bulleted list, you were able to learn about the advantages and disadvantages of a flash drive. Based on this information, we can conclude that this device in fact has few shortcomings that, if desired, can be corrected and modified.
How does a USB drive work?
The principle of operation of a flash drive is based on connecting it to the USB port of a personal computer and subsequent operation by loading and deleting data from it. A USB device is based on the following types of flash memory: NAND or NOR. Flash memory contains silicon crystals, on the basis of which field-effect transistors with insulated or floating gates are placed. The latter, in turn, can hold a charge, in other words, electrons. It should be noted that field-effect transistors have a drain and a source.
When writing to a flash drive, the controller applies a positive voltage to the control gate, thereby causing some of the charge to move from drain to source with a deviation towards the floating gate. Some of the electrons, after deflection, overcome the small insulator layer and then penetrate into the floating gate, where, in turn, they remain for a long time (storage). The storage time is given above in the section on advantages and disadvantages, however, this data will vary for different manufacturers and memory sizes of the flash device.
Flash drive device
The USB storage device is shown in the image. It is worth saying that when a user connects a USB flash drive and then uses it for his own purposes, at that moment very complex processes controlled by the memory controller take place directly in the portable media itself.
The above image contains all the main elements of a “flash drive”, but not all of them. The image below shows the remaining elements of the device
- USB connector for receiving and transmitting data.
- Board control points.
- Quartz resonator.
- LED for signaling the operation of the device.
- Write-protective switch.
- Place for connecting the memory controller.
This is what a portable portable device looks like disassembled and separated into individual circuit components. From the above information, it becomes clearer how a flash drive works. What if it's faulty?
The flash drive does not work: how to restore and what to do
This guide will be brief because if your removable device fails due to physical malfunctions or due to wear and tear of functionality, it will be more expensive to restore it than to buy a new one. You know how a flash drive works, and you also know from the information presented above what it consists of. Unfortunately, you won’t be able to repair it manually without the proper skills, so as a last resort, take the device to a service center.
In order to check the functionality of a flash drive, just connect it one by one to different ports on your computer or reading device. If none of the ports recognizes the flash drive, try connecting it to another computer or device that can read information from the media. If the device is working, it will definitely open. Also, to recognize the device on your computer, you can try updating the USB port driver.
The flash drive is write-protected: how to remove the protection
There are several simple ways to remove write protection from a flash drive. The first method is physical protection installed on the drive case. You can remove it by moving the key to another position (for recording). The second method will be one of the most common solutions to the problem, this is to format the device into a different file system (NTFS and FAT32). An alternative method is to solve the problem through the command line. To do this, start the DiskPart system service through the console interpreter "Run", then enter the command "attributes disk clear readonly", without quotes.
How to properly connect a flash drive to a computer
The correct way to connect a removable drive to a computer is to connect the flash drive connector to a USB port that matches the speed of the device connector model and data transfer speed. Accordingly, this is a 2.0 or 3.0 port, and it can also be a connection method via the latest Type C port, which is currently widely used by Apple on its MacBooks. In some cases, it happens that due to the incompatibility of the port and the flash drive, the computer does not recognize it. Therefore, make the connection correctly.
Conclusion
From the above information in this article, you learned about the origins of the removable drive, its advantages and disadvantages, as well as the complete structure and operating principle of the removable Flash drive. The article discussed how a flash drive works and how to properly connect it to a reading device. We were also able to learn how to remove write protection.
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 tunnel 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, 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.
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 marked 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. An adapter must be used to ensure compatibility with a standard MMC slot.
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 the MMC is the copyright protection technology: the card has cryptographic protection against unauthorized copying, increased information protection against 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).
Information on a flash drive is stored in memory cells, each of which can store one bit: 0 or 1. A flash drive consists of billions of such memory cells.
Memory cell
One memory cell is one bit. One letter in the text is 8 bits or 1 byte. This text takes up approximately 6 thousand bytes, that is, to save it to a flash drive, 48 thousand memory cells will be required. A new episode of House in HD will require approximately 11 billion memory cells. It is difficult to imagine that they will all easily fit into an area of 1 square centimeter.
A memory cell is a transistor. On both sides it has two n-type semiconductors, which have many free electrons that can move freely, that is, carry current.
Between these semiconductors is a p-type semiconductor, which, on the contrary, has a lack of electrons. The current there is carried, accordingly, by holes from missing electrons.
Current cannot pass between n-semiconductors because there is a p-conductor between them, and they have different types of conductivity.
But above the p-semiconductor there is a control gate. This is an electrode to which positive or negative voltage can be applied. If a positive voltage is applied to it, it will push away the holes in the p-semiconductor and attract electrons because opposite charges attract.
The floating gate is surrounded by a dielectric to prevent electrons from escaping from it. Theoretically, a memory cell can store its value indefinitely, or at least for decades.
The result is a so-called n-junction, through which electricity can pass from one n-type semiconductor to another and the transistor can conduct current.
There is a metal plate between the control gate and the p-semiconductor - this is a floating gate. If it is charged negatively, it will interfere with the operation of the control gate, and the transistor will not conduct current, regardless of whether there is a positive voltage at the control gate or not.
How data is read
To check what is written in a memory cell, zero or one, voltage is applied to the control gate and it is checked whether current can flow through the transistor:
- - If there is an excess of electrons on the control gate, then no current will flow, which means it is one.
- - If there is no excess electrons at the control gate, then the current will flow, which means it is zero.
How to record
To write a unit into a memory cell, you need to add electrons to the floating gate. But this is not so easy to do because the floating gate is surrounded by a dielectric, which is known to not conduct current.
The tunnel effect is a phenomenon possible only in quantum mechanics, when, due to its wave properties, an electron jumps from one place to another. That is, it ends up on the other side of the dielectric without passing through it. This is impossible in classical mechanics.
To force electrons into the floating gate, a positive voltage is applied to the control gate - much higher than when reading. Some passing electrons jump onto the floating gate due to the tunneling effect.
Erasing data occurs in exactly the same way, only instead of a positive voltage, a negative voltage is applied to the control gate, and electrons jump off the floating gate.