A few differences between ROM and RAM

Hello everyone, I am still your good friend, the Dragon is less than a lang, today I and everyone explain what is the difference between ROM and ram exactly?

ROM, see the interpretation, that is: Read only memory memory. It can only read information, can not write information, power off after the information is still saved, generally used for it to store fixed system software and fonts. Low access speed and cannot be rewritten relative to ram. Because it can not be rewritten, can not be upgraded, and now rarely used to it, the computer enabled with the BIOS chip is.

RAM, which is the Ramdom access memory read and write memory, the operative language is called: Volatile random access memory, high-speed access, read and write time is equal, and address-independent. such as computer memory. The memory can be read and write with any of the storage units, the information will not be saved after power off, the information needs to be re-loaded after the boot, usually used to store the operating system, various running software, input and output data, intermediate results and external memory exchange information, we often say that the memory refers to RAM.

Here I would like to use a common life of electronic products, computers and mobile phones as a metaphor:

On the computer, we say RAM refers to the computer memory, and ROM generally refers to the bios of a little memory, like a USB flash drive and hard disk.

On the phone, we say RAM refers to the phone running memory, and ROM refers to the phone body storage space and mobile phone operating system.

In addition, it's essentially different from Rom, like two mirrors, it's RAM mirroring, RAM reading it, using it, rewriting it, extending it ...

ROM is the abbreviation for ROM image (read-only memory mirroring). This has to do with the process of the mobile phone brush, which is a process of writing a read-only memory image (ROM image) to read-only memory (ROM). The common ROM image has img, zip and other formats, the former usually with the FastBoot program through the data line brush (line brush), the latter usually in recovery mode from the SD brush (card brush), solid IMG Mirror is also known as the line brush package, zip image is also known as the card brush package. Many custom system developers in China do not know whether the product they are developing is OS or UI, and in order to avoid mixing and arguing, they will call themselves ROM. Now I'm a lot more custom system players will also refer to the custom system as ROM.

RAM, also known as a "random accessor", is the internal memory that directly exchanges data with the CPU, also called main memory. It can be read and written at any time, and is fast, often as a temporary data storage medium for the operating system or other running programs. The data contents of the storage unit can be withdrawn or deposited as needed, and the speed of access is independent of the location of the storage unit. According to the principle of storage unit, random memory is divided into static random memory (Sram,static RAM) and dynamic random memory (Dram,dynamic RAM).

The following excerpt from Baidu, explain the current SRAM and DRAM each have advantages and application areas.

Static storage unit (SRAM)
Storage principle: Data stored by triggers
Unit structure: Six tube nmos or OS configuration
Advantages: Fast speed, easy to use, no need to refresh, very low static power consumption, commonly used as cache
Disadvantages: Many components, low integration, large operating power
Common SRAM Integrated chip: 6116 (2kx8 bit), 6264 (8kx8 bit), 62256 (32kx8 bit), 2114 (1kx4 bit)

Dynamic storage unit (DRAM)
Principle of storage: the principle of charge can be stored by using MOS gate capacitor, it needs to be refreshed (early: three-tube basic unit; now: single-tube basic unit)
Refresh (Regeneration): In order to timely replenish the missing charge to avoid the loss of stored information, the gate capacitor must be timed to recharge the operation of the charge
Refresh time: The time at which the refresh operation is scheduled. The time must be less than the time at which the gate capacitor naturally holds information (less than 2ms).
Advantages: Integration is much higher than SRAM, low power consumption, low price
Disadvantage: Because of the need to refresh the peripheral circuit complex; refresh also makes the access speed slower than DRAM, so in the computer, SRAM is often used as the main memory.
However, because the dram[1] storage unit is simple in structure, with fewer components, high integration and low power consumption, it has become the mainstream product of large capacity ram.

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A few differences between ROM and RAM