Modern computers are the most complex electronic devices, performing millions of simple operations per second.

Thanks to this, we can enjoy complex game worlds, watch movies in high quality images, surf the Internet, etc. Not much inferior to computers are phones, which today are also necessarily equipped with all the necessary attributes of a computing device - a high-performance processor, RAM and permanent memory, abbreviated as RAM and ROM.

What is RAM?

The need for a random access memory device (abbreviated as RAM or RAM) arose already among the very first computers, created in the distant 40s. Buffer memory, as it is sometimes called in other words, is used during the execution of any process.

In fact, all operations performed by the processor use RAM to store intermediate results. The data stored in RAM changes very quickly and is never saved after the computer or phone is turned off.

Volume random access memory selected according to processor speed. Extensive RAM will be of little use in combination with a low-power processor. Accordingly, the most powerful processor will not be able to work effectively when paired with a small amount of RAM.


However, powerful processor you can help by “pinching off” a piece of memory from . This method is not suitable for a telephone, but in desktop computer an experienced user can easily “overclock” by increasing the speed of its processes.

Speaking in simple words RAM is a device used by a computer or phone as a back-end. Intermediate results are recorded there, which are quickly erased and replaced with new ones, also intermediate. When the computer is turned off, the “draft” is destroyed, since there is absolutely no need to store the data recorded in its memory.

What is ROM?

Much more complex are read-only memory devices (abbreviated ROM or ROM), which have one very important property– retain recorded information even when complete shutdown power supply A desktop computer uses several types of ROM:

— integrated circuit, on which the BIOS is recorded, located on motherboard and powered by its own coin cell battery;

— HDD, or hard drive, internal or external placement;

— removable cards memory (flash memory, microSD cards etc.);


— laser discs CD, DVD and their storage devices;

- floppy disks (now completely out of use).

All these devices can be united under one name - read-only storage devices. But, as a rule, when they talk about the ROM of a computer or phone, they mean only the microcircuit in which it is “stitched” basic complex software.

In order to change the information recorded in it, you need special and very complex equipment, regular user under no circumstances will he be able to do this.

Information stored by other types of ROM is divided into several sections according to the degree of importance for the device:

- section for operating system;

— section for programs and applications;

— section for other information.

The operating system of the computer, as well as mobile phone, if desired, you can replace or make corrections to it. However, this should be done with caution and only if you fully understand what these changes will lead to.

If the operation of the OS is disrupted, you will have to contact a specialist to configure it, and maybe even reinstall it. The remaining sections of memory can be special problems erased and overwritten, in whole or in part - this will not affect the performance of the device.


So, the computer's read-only storage device is its “memory”, the information in which is retained even if the power is turned off. ROM can be called a computer's scratch notebook, where only the results of processes are recorded for permanent storage.

Types of ROM

ROM – stands for read-only memory that provides non-volatile storage of information on any physical media. Based on the method of storing information, ROM can be divided into three types:

1. ROM based magnetic principle information storage.

The operating principle of these devices is based on changing the direction of the magnetization vector of sections of a ferromagnet under the influence of an alternating magnetic field in accordance with the values ​​of the bits of the recorded information.

A ferromagnet is a substance capable of possessing magnetization at a temperature below a certain threshold (Curie point) in the absence of an external magnetic field.

Reading of recorded data in such devices is based on the effect of electromagnetic induction or magnetoresistive effect. This principle is implemented in devices with moving media in the form of a disk or tape.

Electromagnetic induction is the effect of the appearance electric current in a closed loop when the magnetic flux passing through it changes.

The magnetoresistive effect is based on the change electrical resistance solid conductor under the influence of an external magnetic field.

Main advantage of this type– large volume of stored information and low cost per unit of stored information. The main disadvantage is the presence of moving parts, large dimensions, low reliability and sensitivity to external influences(vibration, shock, movement, etc.)

2. ROMs based on the optical principle of storing information.

The operating principle of these devices is based on changing the optical properties of a portion of the media, for example, by changing the degree of transparency or reflectance. An example of ROM based on the optical principle of storing information is CD, DVD, BluRay discs.

The main advantage of this type of ROM is the low cost of the media, ease of transportation and the possibility of replication. Flaws - low speed read/write, limited quantity rewrites, the need for a reading device.

3. ROMs based on the electrical principle of storing information.

The operating principle of these devices is based on threshold effects in semiconductor structures - the ability to store and record the presence of charge in an isolated area.

This principle is used in solid state memory– memory that does not require the use of moving parts to read/write data. An example of ROM based on the electrical principle of storing information is flash memory.

The main advantage of this type of ROM is high speed read/write, compactness, reliability, efficiency. Flaws - limited number rewrites.

On this moment Other “exotic” types exist or are under development permanent memory, such as:

Magnetic-optical memory– memory that combines the properties of optical and magnetic storage devices. Writing to such a disk is carried out by heating the cell with a laser to a temperature of about 200 o C. The heated cell loses its magnetic charge. Next, the cell can be cooled, which will mean that a logical zero is written to the cell, or recharged with a magnetic head, which will mean that a logical one is written to the cell.

Once cooled, the magnetic charge of the cell cannot be changed. Reading is performed with a laser beam of lower intensity. If the cells contain a magnetic charge, the laser beam is polarized, and the reader determines whether the laser beam is polarized. Due to the “fixation” of the magnetic charge during cooling, magnetic-optical ones have high reliability of information storage and theoretically can have a recording density greater than ROM based only on the magnetic principle of information storage. However, they cannot replace “hard” drives due to the very low recording speed caused by the need for high heating of the cells.

Magnetic-optical memory is not widely used and is used very rarely.

Molecular memory– memory based on atomic tunneling microscopy technology, which allows individual atoms to be removed or added to molecules, the presence of which can then be read by special sensitive heads. This technology was introduced in mid-1999 by Nanochip, and theoretically made it possible to achieve a packaging density of about 40 Gbit/cm 2, which is tens of times higher than existing serial samples of “Hard” drives, but the recording speed and reliability of the technology are too low to speak of practical use molecular memory in the foreseeable future.

Holographic memory– differs from the existing most common types of permanent memory, which use one or two surface layers for recording, by the ability to write data over the “entire” amount of memory using different angles laser tilt. The most likely use of this type of memory is in ROM based on optical storage of information, where it is no longer a novelty optical discs with several information layers.

There are other, very exotic types of permanent memory, but even in laboratory conditions they balance on the brink of science fiction, so I won’t mention them, we’ll wait and see.

| Read Only Memory (ROM)

Intel 1702 EPROM chip with UV erase
Read-only memory (ROM)- non-volatile memory, used to store an array of immutable data.

Historical types of ROM

Read-only storage devices began to find application in technology long before the advent of computers and electronic devices. In particular, one of the first types of ROM was a cam roller, used in barrel organs, music boxes, and striking clocks.

With development electronic technology and computers there was a need for high-speed ROMs. In the era of vacuum electronics, ROMs were used based on potentialoscopes, monoscopes, and beam lamps. In computers based on transistors, plug matrices were widely used as small-capacity ROMs. If necessary storage large volumes data (for computers of the first generations - several tens of kilobytes), ROMs based on ferrite rings were used (they should not be confused with similar types of RAM). It is from these types of ROM that the term “firmware” originates - the logical state of the cell was set by the direction of winding the wire surrounding the ring. Since a thin wire had to be pulled through a chain of ferrite rings, metal needles similar to sewing needles were used to perform this operation. And the operation of filling the ROM with information itself was reminiscent of the sewing process.

How does ROM work? Modern types of ROM

Very often, in various applications, it is necessary to store information that does not change during the operation of the device. This is information such as programs in microcontrollers, boot loaders and BIOS in computers, tables of digital filter coefficients in signal processors. Almost always this information is not required at the same time, so the simplest devices for storing permanent information can be built on multiplexers. The diagram of such a permanent storage device is shown in the following figure

Read-only memory circuit based on a multiplexer
In this circuit, a read-only memory device with eight single-bit cells is built. Storing a specific bit into a single-digit cell is done by soldering the wire to the power source (writing a one) or sealing the wire to the case (writing a zero). On circuit diagrams such a device is designated as shown in the figure

Designation of a permanent storage device on circuit diagrams
In order to increase the capacity of the ROM memory cell, these microcircuits can be connected in parallel (the outputs and recorded information naturally remain independent). Scheme parallel connection single-bit ROM is shown in the following figure

Multi-bit ROM circuit
In real ROMs, information is recorded using the last operation of chip production - metallization. Metallization is carried out using a mask, which is why such ROMs are called mask ROMs. Another difference between real microcircuits and the simplified model given above is the use of a demultiplexer in addition to a multiplexer. This solution makes it possible to turn a one-dimensional storage structure into a multidimensional one and, thereby, significantly reduce the volume of the decoder circuit required for the operation of the ROM circuit. This situation is illustrated by the following figure:

Mask read-only memory circuit
Mask ROMs are depicted in circuit diagrams as shown in the figure. The addresses of memory cells in this chip are supplied to pins A0 ... A9. The chip is selected by the CS signal. Using this signal, you can increase the volume of ROM (an example of using the CS signal is given in the discussion of RAM). The microcircuit is read using the RD signal.

Programming of the mask ROM is carried out at the manufacturer's factory, which is very inconvenient for small and medium-sized production batches, not to mention the device development stage. Naturally, for large-scale production, mask ROMs are the cheapest type of ROM, and therefore are widely used at present. For small and medium-sized production series of radio equipment, microcircuits have been developed that can be programmed in special devices ah - programmers. In these chips, the permanent connection of conductors in the memory matrix is ​​replaced by fusible links made of polycrystalline silicon. During the production of a microcircuit, all jumpers are made, which is equivalent to writing logical units to all memory cells. During the programming process, increased power is supplied to the power pins and outputs of the microcircuit. In this case, if the supply voltage (logical unit) is supplied to the output of the microcircuit, then no current will flow through the jumper and the jumper will remain intact. If you apply to the output of the microcircuit low level voltage (connect to the body), then a current will flow through the jumper, which will evaporate this jumper and when the information is subsequently read from this cell, a logical zero will be read.

Such microcircuits are called programmable ROM (PROM) and are depicted on circuit diagrams as shown in the figure. As an example, we can name microcircuits 155PE3, 556PT4, 556PT8 and others.

Designation of programmable read-only memory on circuit diagrams
Programmable ROMs have proven to be very convenient for small- and medium-scale production. However, when developing radio-electronic devices, it is often necessary to change the program recorded in ROM. In this case, the EPROM cannot be reused, so once the ROM is written down, if there is an error or an intermediate program, it has to be thrown away, which naturally increases the cost of hardware development. To eliminate this drawback, another type of ROM was developed that could be erased and reprogrammed.

UV erasable ROM is built on the basis of a storage matrix built on memory cells, internal organization which is shown in the following figure:

UV- and electrically erasable ROM memory cell
The cell is a MOS transistor in which the gate is made of polycrystalline silicon. Then, during the manufacturing process of the microcircuit, this gate is oxidized and as a result it will be surrounded by silicon oxide - a dielectric with excellent insulating properties. In the described cell, with the ROM completely erased, there is no charge in the floating gate, and therefore the transistor does not conduct current. When programming the microcircuit, a high voltage is applied to the second gate located above the floating gate and charges are induced into the floating gate due to the tunnel effect. After the programming voltage on the floating gate is removed, the induced charge remains and, therefore, the transistor remains in a conducting state. The charge on a floating gate can be stored for decades.

The structural diagram of a read-only memory device does not differ from the mask ROM described earlier. The only thing that is used instead of a jumper is the cell described above. In reprogrammable ROMs, previously recorded information is erased using ultraviolet radiation. In order for this light to pass freely to semiconductor crystal, a quartz glass window is built into the microcircuit body.

When the microcircuit is irradiated, the insulating properties of silicon oxide are lost and the accumulated charge from the floating gate flows into the volume of the semiconductor and the transistor of the memory cell goes into the off state. The erasing time of the microcircuit ranges from 10 to 30 minutes.

The number of write-erase cycles of microcircuits ranges from 10 to 100 times, after which the microcircuit fails. This is due to the damaging effects of ultraviolet radiation. An example of such microcircuits is the 573 series microcircuits Russian production, microcircuits of the 27cXXX series of foreign production. These chips most often store BIOS programs. universal computers. Reprogrammable ROMs are depicted in circuit diagrams as shown in the figure

Designation of a reprogrammable read-only memory device on circuit diagrams
So, cases with a quartz window are very expensive, as well as the small number of write-erase cycles, which led to the search for ways to erase information from the EPROM electrically. There were many difficulties encountered along this path, which have now been practically resolved. Nowadays, microcircuits with electrical erasure of information are quite widespread. As a storage cell, they use the same cells as in the ROM, but they are erased by electrical potential, so the number of write-erase cycles for these microcircuits reaches 1,000,000 times. The time to erase a memory cell in such microcircuits is reduced to 10 ms. The control circuit for such microcircuits turned out to be complex, so two directions for the development of these microcircuits have emerged:

1. -> EEPROM
2. -> FLASH – ROM

Electrically erasable PROMs are more expensive and smaller in volume, but they allow you to rewrite each memory cell separately. As a result, these chips have maximum number write-erase cycles. The area of ​​application of electrically erasable ROM is the storage of data that should not be erased when the power is turned off. Such microcircuits include domestic microcircuits 573РР3, 558РР and foreign microcircuits of the 28cXX series. Electrically erasable ROMs are designated on the diagrams as shown in the figure.

Designation of electrically erasable read-only memory on circuit diagrams
IN Lately There has been a tendency to reduce the size of EEPROM by reducing the number of external legs of the microcircuits. To do this, the address and data are transferred to and from the chip via a serial port. In this case, two types of serial ports are used - SPI port and I2C port (microcircuits 93cXX and 24cXX series, respectively). Foreign series 24cXX corresponds domestic series 558PPX chips.

FLASH - ROMs differ from EEPROMs in that erasing is not performed on each cell separately, but on the entire microcircuit as a whole or a block of the memory matrix of this microcircuit, as was done in EEPROM.

When accessing a permanent storage device, you first need to set the address of the memory cell on the address bus, and then perform a read operation from the chip. This timing diagram is shown in the figure

Designation FLASH memory on circuit diagrams
The arrows in the figure show the sequence in which control signals should be generated. In this figure, RD is the read signal, A is the cell address select signals (since individual bits on the address bus can receive different meanings, then the transition paths to both the single and zero states are shown), D is the output information read from the selected ROM cell.

Read-only memory (ROM)– A memory designed to store immutable information (programs, constants, table functions). In the process of solving problems, the ROM allows only reading information. As a typical example of the use of ROM, we can indicate the LSI ROM used in PCs to store BIOS (Basic Input Output System - basic system input/output).

In the general case, a ROM storage device (an array of its storage cells) with a capacity of EPROM words, a length of r+ 1 digits each, usually a system of horizontal (address) EPROMS and r+ 1 vertical (discharge) conductors, which at the intersection points can be connected by coupling elements (Fig. 1.46). Communication elements (EC) are fuse-links or p-n-transitions. The presence of an element of connection between j-th horizontal and i th vertical conductors means that in i-th digit of memory cell number j one is written, the absence of ES means that zero is written here. Writing a word to cell number j ROM is produced by proper arrangement of communication elements between the bit conductors and the address wire number j. Reading a word from cell number j The ROM goes like this.

Rice. 1.46. ROM storage with a capacity of EPROM words, a length of r+ 1 digits each

Address code A = j is deciphered, and on the horizontal conductor the number j The drive is supplied with voltage from the power source. Those of the bit conductors that are connected to the selected address conductor by communication elements are energized U 1 level unit, the remaining discharge conductors remain energized U 0 level zero. Set of signals U 0 and U 1 on the bit conductors and forms the contents of the PL number j, namely the word at the address A.

Currently, ROMs are built from LSI ROMs that use semiconductor ES. LSI ROM is usually divided into three classes:

– mask (MPZU);

– programmable (PROM);

– reprogrammable (RPM).

Mask ROMs(ROM - from Read Only Memory) - ROM into which information is written from a photomask during the process of growing a crystal. For example, LSI ROM 555PE4 with a capacity of 2 kbytes is a character generator using the KOI-8 code. The advantage of mask ROMs is their high reliability, but the disadvantage is their low manufacturability.

Programmable ROMs(PROM - Programmable ROM) - ROM, information into which is written by the user using special devices - programmers. LSI data is manufactured with full set ES at all intersection points of address and bit conductors. This increases the manufacturability of such LSIs, and hence their mass production and use. Recording (programming) of information in EEPROM is carried out by the user at the place of their use. This is done by burning out the communication elements at those points where zeros should be written. Let's point out, for example, the TTLSH-BIS PROM 556RT5 with a capacity of 0.5 kbytes. The reliability of EPROM LSIs is lower than that of masked LSIs. Before programming, they must be tested for the presence of ES.

In MPOM and PROM it is impossible to change the contents of their PL. Flashable ROMs(RPM) allow multiple changes of the information stored in them. In fact, RPOM is RAM in which t Salary>> t Thurs. Replacing the contents of the ROM begins with erasing the information stored in it. ROMs with electrical (EEPROM) and ultraviolet (UVEPROM) erasure of information are available. For example, the KM1609RR2A LSI RPOM with electrical erasure with a capacity of 8 kbytes can be reprogrammed at least 104 times, stores information for at least 15,000 hours (about two years) in the on state and at least 10 years in the off state. LSI RPOM with ultraviolet erasure K573RF4A with a capacity of 8 kbytes allows for at least 25 rewrite cycles, stores information in the on state for at least 25,000 hours, and in the off state for at least 100,000 hours.

The main purpose of RPOMs is to use them instead of ROMs in software development and debugging systems, microprocessor systems and others when it is necessary to make changes to programs from time to time.

The operation of a ROM can be considered as a one-to-one conversion N-bit address code A V n-bit code of the word read from it, i.e. ROM is a code converter (digital machine without memory).

In Fig. Figure 1.47 shows a conventional image of a ROM in the diagrams.

Rice. 1.47. Conditional ROM image

The functional diagram of the ROM is shown in Fig. 1.48.

Rice. 1.48. Functional diagram ROM

According to the terminology adopted among storage device specialists, the input code is called an address, 2 n vertical buses - number lines, m outputs - by bits of the stored word. When any ROM enters the input binary code One of the number lines is always selected. In this case, at the output of those OR elements whose connection with a given number line is not destroyed, 1 appears. This means that 1 is written in this bit of the selected word (or number line). At the outputs of those bits whose connection with the selected number line is burned out, zeros will remain. The programming law can also be inverse.

Thus, ROM is a functional unit with n entrances and m outputs storing 2 n m-bit words, which when working digital device do not change. When a ROM address is applied to the input, the word corresponding to it appears at the output. At logical design permanent storage is considered either as a memory with a fixed set of words, or as a code converter.

In the diagrams (see Fig. 1.47), ROM is designated as ROM. Read-only memory devices usually have an E enable input. When the E input level is active, the ROM performs its functions. If there is no resolution, the outputs of the microcircuit are inactive. There can be several enabling inputs, then the microcircuit is unlocked when the signals at these inputs match. In ROM, the E signal is often called reading CT (read), selecting a VM chip, selecting a VC crystal (chip select - CS).

ROM chips are expandable. To increase the number of bits of stored words, all inputs of the microcircuits are connected in parallel (Fig. 1.49, A), and from the increased total number of outputs, the output word is removed according to the increased bit depth.

To increase the number of stored words themselves (Fig. 1.49, b) the address inputs of the microcircuits are switched on in parallel and are considered as the low-order bits of the new, extended address. The added high-order bits of the new address are sent to the decoder, which selects one of the microcircuits using the E inputs. With a small number of microcircuits, decoding of the most significant bits can be done on the conjunction of the enabling inputs of the ROMs themselves. The outputs of the same bits must be combined using OR functions as the number of stored words increases. Special OR elements are not required if the outputs of the ROM chips are made either according to an open collector circuit for combining using the wiring OR method, or according to a three-state buffer circuit, allowing direct physical combining of the outputs.

The outputs of ROM chips are usually inverse, and input E is often inverted. Increasing the ROM may require the introduction of buffer amplifiers to increase the load capacity of some signal sources, taking into account the additional delays introduced by these amplifiers, but in general, with a relatively small volumes memory, which is typical for many control centers (for example, automation devices), increasing ROM usually does not give rise to fundamental problems.

Rice. 1.49. Increasing the number of bits of stored words when microcircuit inputs are connected in parallel and increasing the number of stored words when microcircuit address inputs are connected in parallel

Computers and any electronics are complex devices, the operating principles of which are not always clear to most ordinary people. What is ROM and why is the device needed? Most people will not be able to answer this question. Let's try to correct this misunderstanding. What is ROM?

What are they and where are they used? Read-only memory devices (ROM) are non-volatile memory. Technologically, they are implemented as a microcircuit. At the same time, we learned what the ROM abbreviation is. Devices are designed to store information entered by the user and installed programs. In the permanent storage device you can find documents, melodies, pictures - i.e. anything that needs to be stored for months or even years. Memory volumes, depending on the device used, can vary from several kilobytes (on the simplest devices that have a single silicon chip, an example of which are microcontrollers) to terabytes. The larger the ROM capacity, the more objects can be stored. The volume is directly proportional to the amount of data. If we condense the answer to the question of what a ROM is, we should answer: it is a data storage that does not depend on constant voltage. Hard disks as primary permanent storage devices The question of what ROM is has already been answered. Now we should talk about what they are. The main permanent storage devices are hard disks. They are in everyone modern computer. They are used due to their wide capabilities for storing information. But at the same time, there are a number of ROMs that use multiplexers (these are microcontrollers, bootloaders and other similar electronic mechanisms). At detailed study It will be necessary not only to understand the meaning of the ROM. Decoding other terms is also necessary in order to understand the topic. Expansion and addition of ROM capabilities thanks to flash technologies

If the standard amount of memory is not enough for the user, then you can use additional extension capabilities of the provided ROM in the field of data storage. This is done through modern technologies, implemented in memory cards and USB flash drives. They are based on the principle of reusable use. In other words, data on them can be erased and written tens or hundreds of thousands of times. What does read-only memory consist of?

The ROM contains two parts, which are designated as ROM-A (for storing programs) and ROM-E (for issuing programs). A type A read-only memory device is a diode-transformer matrix, which is stitched using address wires. This section of ROM performs main function. The filling depends on the material from which the ROM is made (punched and magnetic tapes, punched cards, magnetic disks, drums, ferrite tips, dielectrics and their property of accumulating electrostatic charges can be used). Schematic structure of ROM

This electronics object is depicted as a device that appearance resembles a connection a certain number single-digit cells. The ROM chip, despite its potential complexity and seemingly significant capabilities, is small in size. When storing a certain bit, it is sealed to the case (when a zero is written) or to the power source (when a unit is written). To increase the capacity of memory cells in permanent storage devices, microcircuits can be connected in parallel. This is what manufacturers do to get a modern product, because a high-performance ROM chip allows them to be competitive in the market. Memory volumes when used in various units of equipment

Memory sizes vary depending on the type and purpose of the ROM. So in simple household appliances like washing machines or refrigerators, you can have enough installed microcontrollers (with their reserves of several tens of kilobytes), and in rare cases something more complex is installed. It makes no sense to use a large amount of ROM here, because the amount of electronics is small and the equipment is not required complex calculations. For modern TVs something more perfect is required. And the pinnacle of complexity is Computer Engineering like computers and servers, ROMs for which, at a minimum, hold from several gigabytes (for those released 15 years ago) to tens and hundreds of terabytes of information. Mask ROM

In cases where recording is carried out using a metallization process and a mask is used, such a read-only memory device is called masked. The addresses of the memory cells in them are supplied to 10 pins, and a specific chip is selected using a special CS signal. Programming of this type of ROM is carried out in factories, as a result of which production in small and medium volumes is unprofitable and rather inconvenient. But when produced in large quantities, they are the cheapest among all permanent storage devices, which has ensured their popularity. Schematically, they differ from the general mass in that in the memory matrix the conductor connections are replaced by fusible jumpers made of polycrystalline silicon. At the production stage, all jumpers are created, and the computer believes that logical ones are written everywhere. But during preparatory programming, increased voltage is applied, with the help of which logical units are left. When low voltages are applied, the jumpers evaporate and the computer reads that there is a logical zero. Programmable read only memory devices operate on this principle. Programmable read-only memory devices (PROMs) have proven to be convenient enough in the manufacturing process to be used in medium- and small-scale production. But such devices also have their limitations - for example, a program can only be written once (due to the fact that the jumpers evaporate once and for all). Due to this inability to reuse a permanent storage device, if it is written incorrectly, it must be thrown away. As a result, the cost of all manufactured equipment increases. Due to the imperfection of the production cycle, this problem was quite on the minds of memory device developers. The way out of this situation was the development of ROM, which can be re-programmed many times. UV or electrical erasable ROM

And such devices were called “ultraviolet or electrically erasable read only memory.” They are created on the basis of a memory matrix, in which memory cells have a special structure. Thus, each cell is a MOS transistor in which the gate is made of polycrystalline silicon. Similar to the previous option, right? But the peculiarity of these ROMs is that the silicon is additionally surrounded by a dielectric that has wonderful insulating properties - silicon dioxide. The operating principle here is based on the content of an inductive charge, which can be stored for decades. There are specifics to erasing. Thus, an ultraviolet ROM device requires exposure to ultraviolet rays coming from outside (ultraviolet lamp, etc.). Obviously, from the point of view of simplicity, the operation of electrically erasable read-only memories is optimal, since they simply need to be activated by applying voltage. The principle of electrical erasure has been successfully implemented in ROMs such as flash drives, which can be seen in many. But such a ROM circuit, with the exception of cell construction, is structurally no different from a conventional masked read-only memory device. Sometimes such devices are also called reprogrammable. But with all the advantages, there are also certain limits to the speed of erasing information: this action usually takes about 10-30 minutes. Despite the ability to rewrite, reprogrammable devices have limitations on their use. Thus, electronics with ultraviolet erasure can survive from 10 to 100 rewrite cycles. Then the destructive influence of radiation becomes so noticeable that they cease to function. You can see the use of such elements as storage for BIOS programs, in video and sound cards, for additional ports. But the optimal principle regarding rewriting is the principle of electrical erasure. Thus, the number of rewrites in ordinary devices ranges from 100,000 to 500,000! There are separate ROM devices that can do more, but most users have no use for them.