what is memory

Memory is a memory device in a computer system, used to store programs and data; all information in the computer, including input raw data, computer programs, intermediate running results and final running results are stored in the memory. The memory stores and retrieves information based on locations specified by the controller.

The operating environment of this tutorial: Windows 10 system, DELL G3 computer.

What is memory

Memory (Memory) is a memory device in a computer system, used to store programs and data. All information in the computer, including input raw data, computer programs, intermediate results and final results are stored in memory. It stores and retrieves information based on locations specified by the controller.

Composition of memory:

The storage medium that makes up the memory currently mainly uses semiconductor devices and magnetic materials. The smallest storage unit in memory is a bistable semiconductor circuit or a CMOS transistor or a storage element of magnetic material, which can store a binary code. A storage unit is composed of several storage units, and a memory is composed of many storage units. A memory contains many storage units, each of which can store one byte. The location of each storage unit has a number, that is, an address, generally expressed in hexadecimal. The sum of the data that can be stored in all storage units in a memory is called its storage capacity. Assuming that the address code of a memory consists of 20 binary numbers (i.e. 5 hexadecimal digits), it can represent 220, which is 1M storage unit addresses. Each storage unit stores one byte, so the storage capacity of the memory is 1KB.

Three categories of memory:

1. Random access memory

Random access memory (RAM), also known as "random access memory", is an internal memory that directly exchanges data with the CPU, also called main memory (memory). It can be read and written at any time, is very fast, and is often used as a temporary data storage medium for the operating system or other running programs.

Random access memory features

Random access. The so-called "random access" means that when data in the memory is read or written, the time required has nothing to do with the location of the information or the location where it is written. In contrast, when reading or writing information in a Sequential Access storage device, the time and location required are related. It is mainly used to store the operating system, various applications, data, etc.

Volatility. RAM cannot retain data when power is turned off. If data needs to be saved, they must be written to SRAM on a long-term storage device (such as a hard disk). Compared with RAM and ROM, the biggest difference between the two is that the data stored in RAM will disappear automatically after the power is turned off, while ROM will not disappear automatically and can be saved for a long time without power.

Sensitive to static electricity. Like other delicate integrated circuits, random access memory is very sensitive to environmental electrostatic charges. Static electricity can interfere with the charge of the capacitors in the memory, causing data loss or even burning out the circuit. Therefore, before touching the random access memory, you should first touch the metal ground with your hand.

Access speed. Modern random access memory has the fastest write and read speeds of almost any access device, and the access latency of laptop memory is negligible compared to other storage devices that involve mechanical operations.

Need to refresh (regenerate). Modern random access memory relies on capacitors to store data. A fully charged capacitor represents a 1 (binary), and an uncharged capacitor represents a 0. Since capacitors have leakage to some extent, data will gradually be lost over time if no special treatment is taken. Refreshing means periodically reading the status of the capacitor and then recharging the capacitor according to its original status to make up for the lost charge. The need to refresh explains exactly the volatile nature of random access memory.

2. Read-Only Memory

Read-Only Memory (English: Read-Only Memory, abbreviated as: 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.

Characteristics of read-only memory

The characteristic of read-only memory is that it can only read information and cannot write information at will. A basic input/output system is solidified in the ROM on the motherboard, called BIOS. (Basic Input Output System). Its main function is to complete the power-on self-test of the system, initialization of each functional module in the system, basic input/output driver of the system and boot operating system.

3. External memory

External storage refers to storage other than computer memory and CPU cache. This type of storage can generally still save data after the power is turned off. Common external memories include hard disks, floppy disks, optical disks, U disks, etc.

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