computer rom refers to

ROM is the abbreviation of Read-Only Memory. It is a solid-state semiconductor memory that can only read out previously stored data. Its characteristic is that once the data is stored, it cannot be changed or deleted. Usually used in electronic or computer systems that do not need to change data frequently, and the data will not disappear when the power is turned off.

Introduction

The English abbreviation is ROM. The data stored in ROM is generally written in advance before being installed into the whole machine. It can only be read out during the operation of the whole machine, and cannot be rewritten quickly and conveniently like random access memory. The data stored in ROM is stable and will not change after power failure; its structure is relatively simple and easy to read, so it is often used to store various fixed programs and data. Except for a few types of read-only memories (such as character generators) that can be used universally, the contents of the read-only memories required by different users are different. For ease of use and mass production, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM) and electrically erasable programmable read-only memory ROM (EEPROM) have been further developed. For example, the boot program (operating system) of early personal computers such as Apple II or IBM PC XT/AT or the firmware (Firmware) in various other microcomputer systems.

EPROM needs to be erased with UV light, which is inconvenient and unstable. The EEPROM produced in the 1980s overcame the shortcomings of EPROM, but its integration level was not high and the price was relatively expensive. Therefore, a new type of flash memory with a memory cell structure similar to EPROM was developed. It has high integration, low power consumption, small size, and can be quickly erased online. Therefore, it has developed rapidly and may replace the current hard disk and floppy disk to become the main large-capacity storage media. Most read-only memories are made from metal-oxide-semiconductor (MOS) field-effect transistors.

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Type

##1.ROM

Read-Only Memory is a type of memory that can only be read Data storage. During the manufacturing process, data is burned into the circuit with a special mask. The data content cannot be changed after writing, so it is sometimes called "mask read-only memory" (mask ROM). The manufacturing cost of this memory is low, and it is often used for startup in computers, such as boot CDs. When the system is installed on the computer, the computer reads the operating system files in the C drive directory into the memory, and then calls various accessories through the CPU. When working, the system stores memory in RAM. This type of CD is a COMPACT DISC laser disc, which is what CDs are like.

2.PROM

There is a determinant fuse inside the Programmable ROM (PROM), which needs to be blown by current. , write the required data, but it can only be written once. When the PROM leaves the factory, the stored content is all 1, and the user can write data 0 into some of the units as needed (some PROMs have all data as 0 when they leave the factory, so the user can write 1 into some of the units) , to achieve the purpose of "programming" it. A typical PROM product is a "bipolar fuse structure". If we want to rewrite certain units, we can pass a large enough current to these units and maintain it for a certain period of time. The original fuse will be blown, so that The effect of rewriting some bits is achieved. Another type of classic PROM is a PROM using a "Schottky diode". When it leaves the factory, the diode is in a reverse cutoff state, and a large current method is used to apply the reverse voltage to the "Schottky diode", causing it to Permanent breakdown is enough.

3.EPROM

Erasable Programmable Read Only Memory (EPROM) can use high voltage to program, write and erase data. By exposing the circuit to ultraviolet light, the data can be cleared and reused. Usually a quartz transparent window is reserved on the package shell to facilitate exposure.

4.OTPROM

The writing principle of One Time Programmable Read Only Memory (OTPROM) is the same as EPROM, but in order to save costs, programming and writing Once entered, it will not be erased, so no transparent window is set.

5.EEPROM

The operating principle of Electronically Erasable Programmable Read Only Memory (EEPROM) is similar to EPROM, but it is erased The method is done using a high electric field, so no transparent window is required.

6. Flash memory

Each memory cell of flash memory has a "control gate" and a "floating gate". The electric field changes the threshold voltage of the floating gate to perform programmed actions.

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