Purpose and characteristics of ROM. Read-only memory devices (ROM): principle of operation, classification, characteristics ROM is used

Adviсe

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 a 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 something that does not depend on constant voltage.

Hard drives as primary permanent storage devices

The question of what a ROM is has already been answered. Now we should talk about what they are. The main permanent storage devices are hard drives. They are in every 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, bootloaders and other similar electronic mechanisms). With a detailed study, it will be necessary not only to understand the meaning of 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 one is not enough for the user, then you can take advantage of the additional expansion of the capabilities of the provided ROM in the field of data storage. This is done using 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). Type A ROM is a diode-transformer matrix, which is stitched using address wires. This section of ROM performs the 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 in appearance resembles the connection of a certain number of 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. There is no point in using a large amount of ROM here, because the amount of electronics is small and the equipment does not require complex calculations. Modern TVs require something more advanced. And the pinnacle of complexity is computer technology 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 turned out to be convenient enough in the process of technological manufacturing that they could 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.

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Novgorod State University named after. Ya the Wise

Essay

On the topic “Read-only storage devices. Main characteristics, scope"

Completed by: 1st year student gr. 5261

Bronina Ksenia

Checked by: Arkhipova Gelirya Askhatovna

Veliky Novgorod, 2016

1. The concept of read-only storage

1.1 Main characteristics of ROM

1.2 ROM classification

1.2.1 By type of execution

1.2.2 By types of ROM chips

1.2.3 By the method of programming microcircuits (writing firmware to them)

2. Application

3. Historical types of ROM

Literature

1. The concept of read-only storage

Read-only memory (ROM, or ROM - Read Only Memory) is also built on the basis of modules (cassettes) installed on the motherboard and is used to store immutable information: operating system boot programs, computer device testing programs and some drivers basic input/output system (BIOS), etc.

Read-only memory includes read-only memory, ROM (in English-language literature - Read Only Memory, ROM, which literally translates as “read-only memory”), reprogrammable ROM, PROM (in English-language literature - Programmable Read Only Memory, PROM), and flash memory. The name of the ROM speaks for itself. Information in ROM is written at the factory of the memory chip manufacturer, and its value cannot be changed in the future. ROM stores information critical to the computer, which does not depend on the choice of operating system. Programmable ROM differs from conventional ROM in that the information on this chip can be erased using special methods (for example, ultraviolet rays), after which the user can re-write information to it. This information cannot be deleted until the next erase operation.

ROM usually includes non-volatile permanent and “semi-permanent” storage devices, from which information can only be quickly read; information is written to ROM outside of a PC in the laboratory or with a special programmer and in a computer. Based on the information recording technology, the following types of ROM can be distinguished:

§ microcircuits that are programmable only at the time of manufacture - classic or masked ROM or ROM;

§ microcircuits that are programmed once in the laboratory - programmable ROM (PROM), or programmable ROM (PROM);

§ microcircuits that are programmed repeatedly - reprogrammable ROM or erasable PROM (EPROM). Among them, electrically reprogrammable EEPROM (Electrical Erasable PROM) chips, including flash memory, should be noted.

1.1 Main characteristics of ROM

Data in read-only memory (ROM) is stored permanently. Data that is stored permanently is called non-volatile, meaning that it is retained in ROM even when the power is turned off. Once data is written to ROM, it can be read by other devices, but new data cannot be written to ROM.

ROM is most commonly used to store what is called a “monitor program.” A monitor program is a machine program that allows the user of a microcomputer system to view and change all functions of the system, including memory. Another common use of ROM is to store fixed tables of data, such as mathematical functions, that never change.

There are four types of ROM commonly used by digital computer systems: mask-programmed ROM, programmable ROM (PROM), erasable programmable ROM (EPROM), and electrically programmable ROM (EPROM).

1.2 ROM classification

1.2.1 By type of execution

The data array is combined with the sampling device(reading device), in this case the data array is often called “firmware” in conversation:

§ ROM chip;

§ One of the internal resources of a single-chip microcomputer (microcontroller), usually FlashROM.

The data array exists independently:

§ CD;

§ punched card;

§ punched paper tape;

§ barcodes;

§ mounting “1” and mounting “0”.

1.2.2 By types of ROM chips

According to crystal manufacturing technology:

§ R.O. M English read-only memory - read-only memory, mask ROM, is manufactured using the factory method. There is no possibility to change the recorded data in the future.

Figure 1. Mask ROM

§ PRO M English programmable read-only memory -- programmable ROM, flashed once by the user.

Figure 2. Programmable ROM

§ EPROM English. erasable programmable read-only memory - reprogrammable/reprogrammable ROM (PRPZU/RPZU)). For example, the contents of the K573RF1 chip were erased using an ultraviolet lamp. To allow ultraviolet rays to pass to the crystal, a window with quartz glass was provided in the microcircuit housing.

Figure 3. Flashable ROM

§ EEPROM English. electrically erasable programmable read-only memory - electrically erasable reprogrammable ROM). This type of memory can be erased and refilled with data several tens of thousands of times. Used in solid state drives. One of the types of EEPROM is flash memory.

Figure 4. Erasable ROM

§ ROM on magnetic domains, for example K1602RTs5, had a complex sampling device and stored a fairly large amount of data in the form of magnetized areas of the crystal, while having no moving parts (see Computer memory). An unlimited number of rewrite cycles was provided.

§ NVRAM, non-volatile memory - “non-volatile” memory, strictly speaking, is not ROM. This is a small-volume RAM, structurally combined with a battery. In the USSR, such devices were often called “Dallas” after the company that launched them on the market. In NVRAM of modern computers, the battery is no longer structurally connected to the RAM and can be replaced.

By type of access:

§ With parallel access (parallel mode or random access): such a ROM can be accessed in the system in the RAM address space. For example, K573RF5;

§ With sequential access: such ROMs are often used for one-time loading of constants or firmware into a processor or FPGA, used to store TV channel settings, etc. For example, 93С46, AT17LV512A.

1.2.3 According to the method of programming microcircuits (writing firmware to them)

§ Non-programmable ROMs;

§ ROMs programmed only with the help of a special device - a ROM programmer (both once and repeatedly flashed). The use of a programmer is necessary, in particular, for supplying non-standard and relatively high voltages (up to +/- 27 V) to special terminals.

§ In-circuit (re)programmable ROMs (ISP, in-system programming) - such microcircuits have inside a generator of all the necessary high voltages, and can be reflashed without a programmer and even without desoldering from a printed circuit board, using software.

memory chip programming monoscope

2. Application

The firmware for controlling a technical device is often written into permanent memory: a TV, a cell phone, various controllers, or a computer (BIOS or OpenBoot on SPARC machines).

BootROM is firmware such that if it is written to a suitable ROM chip installed in the network card, it becomes possible to load the operating system onto the computer from a remote local network node. For network cards built into the computer, BootROM can be activated through the BIOS.

ROM in IBM PC-compatible computers is located in the address space from F600:0000 to FD00:0FFF

3. 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 the development of electronic technology and computers, the need for high-speed ROMs arose. 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 it was necessary to store large amounts of data (for first-generation computers - 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.

Literature

Ugryumov E. P. Digital circuitry BHV-Petersburg (2005) Chapter 5.

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Random Access Memory (RAM)

RAM is a type of memory that allows stored data to be accessed in any order and from any physical location in memory. RAM can be read and written with new data. The main advantage of RAM is that it takes almost the same time to access any data, regardless of the location of the data. This makes RAM a very fast memory. Computers can read from memory very quickly, and they can also write new data into RAM very quickly.

What does RAM look like?

Commercially available regular memory chips can be easily plugged into and connected to the output of a computer's motherboard. The following picture shows the memory chips.

Read-only memory (ROM)

As the name suggests, data is written to ROM only once and forever. After this, the data can only be read by computers. Read-only memory is often used to install permanent instructions into a computer. These instructions will never change. ROM chips store basic input/output system(BIOS) of the computer. The following figure shows a commercially available ROM BIOS chip.

Difference between RAM and ROM

The following table lists the main differences between random access And only For reading memory.

Comparison table of RAM and ROM

	RAM	ROM
1.	Stands for RANDON-memory access	Stands for memory only For reading
2.	RAM for reading and writing to memory	Typically, ROM is permanent storage and cannot be overwritten. However, the EPROM can be reprogrammed
3.	RAM is faster	ROM is relatively slower than RAM
4.	RAM is non-volatile storage device. This means that data in RAM will be lost if the power supply cuts out.	ROM is read-only memory. The data in the ROM will remain as is even if we remove the power supply
5.	There are basically two types of RAM; static random access memory And dynamic RAM	There are several types of ROM; EPROM, Programmable ROM, EPROM, etc.
6.	RAM stores all applications and data when the computer is running normally	ROM typically stores the instructions needed to start (boot) the computer
7.	The price of RAM is relatively high	ROM chips are comparatively cheaper
8.	larger memory chips	ROM chips are smaller in size
9.	The processor can directly access the contents of memory	The contents of ROM are typically transferred to RAM first and then accessed by the processor. This is done in order to be able to access the contents of the disk at a higher speed.
10.	RAM is often installed with a large amount of memory.	The capacity of the ROM storage device installed in the computer is much less than RAM

RAM and ROM are an integral part of a modern computer system. Do you want to know when the disk is running and when the RAM is in play? Well, when you switch on your computer, you may see a black screen with some white text. This text is from ROM. The ROM instructions control your computer for the first few seconds you turn it on. During this period, as instructions " , how to read from hard drive" "how to print on screen" loaded from ROM. Once the computer is able to do these basic operations, the operating system (Windows/Linux/OSX, etc.) is read from the hard drive and loaded into RAM. The following video explains RAM vs ROM concept further.

When you open a program, like Microsoft Word, the program is loaded from your computer's hard drive into RAM.

We hope this article helped you understand the main differences between RAM and ROM. If you have any questions related to this topic, please feel free to ask in the comment section. We will try to help you. Thank you for using TechWelkin!

Types of ROM

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

1. ROMs based on the magnetic principle of storing information.

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 generation of electric current in a closed circuit when the magnetic flux passing through it changes.

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

The main advantage of this type is the large volume of stored information and the 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. Disadvantages - low read/write speed, limited number of rewrites, 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 read/write speed, compactness, reliability, and efficiency. Disadvantages - limited number of rewrites.

At the moment, other, “exotic” types of permanent memory exist or are at the development stage, such as:

Magnetic-optical memory– memory that combines the properties of optical and magnetic storage. 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 presented 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 too low recording speed and reliability of the technology do not allow us to talk about practical use of 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 record data over the “entire” memory volume using different laser angles. The most likely use of this type of memory is in ROM based on optical information storage, where optical disks with several information layers are no longer a novelty.

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.

Last file update date: 10/23/2009

Read Only Memory (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 (BIOS) in computers, tables of digital filter coefficients in , and , tables of sine and cosine in NCO and DDS. Almost always this information is not required at the same time, so the simplest devices for storing permanent information (ROM) can be built on multiplexers. Sometimes in translated literature, permanent storage devices are called ROM (read only memory). The diagram of such a read-only memory (ROM) is shown in Figure 1.

Figure 1. Read-only memory (ROM) circuit built 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 Figure 2.

Figure 2. 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). The parallel connection diagram of single-bit ROMs is shown in Figure 3.

Figure 3. Multi-bit ROM circuit diagram

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, in addition to a multiplexer, a . This solution makes it possible to turn a one-dimensional storage structure into a two-dimensional one and, thereby, significantly reduce the amount of circuitry required for the operation of the ROM circuit. This situation is illustrated by the following figure:

Figure 4. Masked read-only memory (ROM) circuit diagram

Mask ROMs are depicted in circuit diagrams as shown in Figure 5. 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). The microcircuit is read using the RD signal.

Figure 5. Mask ROM (ROM) on circuit diagrams

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 were developed that can be programmed in special devices - programmers. In these ROMs, the permanent connection of conductors in the memory matrix is replaced by fusible links made of polycrystalline silicon. During ROM production, all jumpers are made, which is equivalent to writing logical units to all ROM memory cells. During the ROM programming process, increased power is supplied to the power pins and outputs of the microcircuit. In this case, if the supply voltage (logical one) is supplied to the output of the ROM, then no current will flow through the jumper and the jumper will remain intact. If a low voltage level is applied to the output of the ROM (connected to the case), then a current will flow through the jumper of the memory matrix, which will evaporate it and when the information is subsequently read from this ROM cell, a logical zero will be read.

Such microcircuits are called programmable ROM (PROM) or PROM and are depicted on circuit diagrams as shown in Figure 6. As an example of PROM, we can name microcircuits 155PE3, 556RT4, 556RT8 and others.

Figure 6. Graphic designation of a programmable read-only memory (PROM) 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, the internal structure of which is shown in the following figure:

Figure 7. 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 chip, 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 ROM, 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 tunneling effect. After the programming voltage is removed, the induced charge remains on the floating gate and hence the transistor remains in a conducting state. The charge on the floating gate of such a cell can be stored for decades.

The described read only memory does not differ from the previously described mask ROM. The only difference is that instead of a fusible jumper, the cell described above is used. This type of ROM is called reprogrammable read only memory (EPROM) or EPROM. In ROM, previously recorded information is erased using ultraviolet radiation. In order for this light to pass freely to the semiconductor crystal, a quartz glass window is built into the housing of the ROM chip.

Figure 8. Appearance of an erasable read only memory (EPROM)

When an EPROM chip is irradiated, the insulating properties of silicon oxide are lost, 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 RPOM chip ranges from 10 to 30 minutes.

Purpose and characteristics of ROM. Read-only memory devices (ROM): principle of operation, classification, characteristics ROM is used

What is ROM?

Hard drives as primary permanent storage devices

Expansion and addition of ROM capabilities thanks to flash technologies

What does read-only memory consist of?

Schematic structure of ROM

Memory volumes when used in various units of equipment

Mask ROM

Programmable Read Only Memory Devices

UV or electrical erasable ROM

Send your good work in the knowledge base is simple. Use the form below

1. The concept of read-only storage

1.1 Main characteristics of ROM

1.2 ROM classification

1.2.1 By type of execution

The data array is combined with the sampling device(reading device), in this case the data array is often called “firmware” in conversation:

1.2.2 By types of ROM chips

According to crystal manufacturing technology:

By type of access:

2. Application

3. Historical types of ROM

Literature

Similar documents

Random Access Memory (RAM)

What does RAM look like?

Read-only memory (ROM)

Difference between RAM and ROM

Types of ROM

Read Only Memory (ROM)

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