Classification of the Memories

The characteristic of RAM is that when the computer is turned on, all the running data and programs of the operating system and application programs will be put in it, and the data stored in it can be modified and accessed at any time. Its work needs continuous power supply. Once the system is powered off, all data and programs stored in it will be automatically emptied and can never be recovered.

According to different components, RAM memory is divided into the following eighteen types:

0 1. dynamic random access memory

This is the most common RAM. The electron tube and the capacitor form a bit storage unit. DRAM stores each storage bit as a charge in a bit memory cell, and uses the charging and discharging of the capacitor to do the storage action. However, due to the leakage problem of the capacitor itself, it must be refreshed every few microseconds, otherwise the data will be lost. The access time is consistent with the discharge time, which is about 2 ~ 4 ms Because of its low cost, it is usually used as the main memory in computers.

02. Static random access memory.

Static means that the data in the memory can stay in it for a long time without access at any time. Every six tubes make up a bit memory cell. Because there is no capacitor, it can work normally without constant charging, so it can be faster and more stable than the general dynamic random access memory, and is often used as a cache.

03. Video memory

Its main function is to output the video data of the graphics card to the digital-to-analog converter, which effectively reduces the workload of the drawing display chip. It is designed with dual data ports, one of which is a parallel data output port and the other is a serial data output port. Mostly used for high-end memory in advanced graphics cards.

04.FPM DRAM (Fast Page Mode DRAM).

Most of the improved versions of DRAM are 72-pin or 30-pin modules. When accessing one bit of data, the traditional DRAM must send the row address and column address once to read and write the data. However, after the row address is triggered by FRM DRAM, if the addresses required by the CPU are in the same row, the column address can be output continuously without the row address. Because the addresses of general programs and data are arranged continuously in the memory, in this case, the required data can be obtained by continuously outputting row addresses and column addresses. FPM divides the memory into many pages, ranging from 5 12B to several KB. When reading data in continuous areas, the data in each page can be read directly through the fast page change mode, which greatly improves the reading speed. 96 years ago, in the 486 era and the early Pentium era, FPM DRAM was widely used.

05.EDO DRAM (Extended Data Output DRAM).

This is a kind of memory after FPM, generally 72Pin and 168Pin modules. It doesn't need to output row address and column address for a period of time when accessing each bit of data like FPM DRAM, and then it can read and write valid data, and can't output the address of the next bit until this reading and writing operation is completed. Therefore, the waiting time of output address can be greatly shortened, and its access speed is generally about 15% faster than that of FPM mode. Generally applicable to the standard memory of Pentium motherboards below mid-range. In the later period, 486 system began to support Edo DRAM, and 1996 began to realize Edo DRAM. .

06. Burst expansion data output DRAM.

This is an improved EDO DRAM, which was proposed by Meguiar. It adds an address counter on the chip to track the next address. It is a burst reading mode, that is, when sending a data address, it only takes one cycle to read each of the remaining three data, so it can access multiple groups of data at a time, which is faster than EDO DRAM. However, few motherboards support BEDO DRAM memory, and only a few motherboards provide support (for example, through APOLLO VP2), so it was quickly replaced by DRAM.

07. Multi-bank DRAM.

A memory specification proposed by MoSys Company is divided into several different types of small libraries, that is, it is composed of several independent small identity matrix. Each library is connected with each other at a higher data speed than the outside, which is generally used for high-speed display cards or accelerator cards, and a few motherboards are used for L2 cache.

08.WRAM (window RAM).

The memory mode developed by Samsung in South Korea is an improved version of VRAM memory. The difference is that its control circuit has 10-20 groups of input/output controllers, and adopts the data access mode of EDO, so the speed is relatively fast. In addition, it also provides a block shift function (BitBlt), which can be applied to professional drawing work.

09.RDRAM(Rambus DRAM)。

Rambus company independently designed a memory mode, the speed can generally reach 500~530MB/s, which is more than 10 times that of DRAM. The memory controller needs to make considerable changes after using this kind of memory, so it is generally used in professional graphics acceleration adapter cards or video game consoles.

10. Synchronous dynamic random access memory

This is a memory mode that can be synchronized with the external clock of CPU. Generally, 168Pin memory module is used, and the working voltage is 3.3V The so-called clock synchronization means that the memory can access data synchronously with the CPU, which can cancel the waiting period and reduce the delay of data transmission, thus improving the performance and efficiency of the computer.

1 1.s gram (synchronous graphics ram).

An improved version of SDRAM uses blocks, that is, every 32 bits as the basic access unit, to retrieve or modify the accessed data separately, so as to reduce the reading and writing times of the whole memory. In addition, a drawing controller is added to meet the drawing requirements, providing a block move function (BitBlt), which is obviously higher than SDRAM.

12. Synchronous burst SRAM

General SRAM is asynchronous. In order to adapt to the faster and faster speed of CPU, it is necessary to synchronize its working clock with the system, which is the reason why SB SRAM appears.

13. pipeline burst SRAM

The rapid increase of CPU external frequency speed puts forward higher requirements for its matching memory. It is an inevitable choice to replace synchronous explosive SRAM with pipeline explosive SRAM, because it can effectively prolong the access clock and thus effectively improve the access speed.

14. Double data rate synchronous dynamic random access memory

As a replacement product of SDRAM, it has two characteristics: first, it is twice as fast as SDRAM; Secondly, DLL (Delay Locked Loop) is used to provide the data filtered signal. This is the mainstream mode of the current memory market.

15. Synchronize the link.

This is an extended SDRAM memory, which improves the logic control circuit and adds a more advanced synchronization circuit. But because of the technical demonstration, it is not difficult to put it into practice.

16.CDRAM (cache DRAM).

This is the first patented technology developed by mitsubishi electric Company. It inserts an SRAM as a secondary cache between the external pin of the DRAM chip and the internal DRAM. At present, almost all CPUs are equipped with a first-level cache to improve efficiency. With the doubling of CPU clock frequency, the influence of cache not being selected will become more and more serious, and the second-level cache provided by CACHE DRAM just supplements the shortage of CPU first-level cache, so it can greatly improve CPU efficiency.

17.DDR II (double data rate synchronous DRAM, second generation synchronous double rate dynamic random access memory)

DDRII is a new standard in the future after the dissolution of DDR's original SLDRAM alliance in 1999 and the integration of existing R&D achievements and DDR. The detailed specifications of DDRII have not yet been determined.

18. Direct Rambus DRAM

It is one of the mainstream memory standards of the next generation, designed and developed by RamBus Company. Connecting all pins to a bus with the same * * * * can not only reduce the size of the controller, but also increase the efficiency of data transmission.

Second, ROM (Read Only Memory)

ROM is the simplest semiconductor circuit. It is manufactured at one time by mask technology. Under the condition that the components work normally, the codes and data in ROM will be permanently saved and cannot be modified. Generally used in PC system program code, BIOS (basic input and output system) on the motherboard, etc. Its reading speed is much slower than RAM.

According to the different components, ROM memory is divided into the following five types:

1. mask read-only memory (mask model read-only memory)

In order to mass-produce ROM memory, manufacturers need to make a ROM or EPROM as a sample from the original data, and then make a large number of copies. This sample is a mask ROM, and the data recorded in the mask ROM can never be modified. Its cost is relatively low.

2. Programmable read-only memory.

This is a ROM memory, in which data can be written by a burner, but only once, so it is also called "OTP-ROM". When the PROM leaves the factory, the stored contents are all 1, and users can write some cells into data 0 as needed (some PROMs are all data 0 when they leave the factory, so users can write some cells into 1) to achieve the purpose of "programming".

3.EPROM (erasable programmable).

This is an erasable read-only memory, which can be reprogrammed after erasure. Before writing, the transparent window on its IC card must be irradiated with ultraviolet rays to clear the contents inside. This kind of chip is easy to identify, and its packaging has "timely glass windows". The "timely glass window" of the programmed EPROM chip is usually covered with black self-adhesive paper to prevent direct sunlight.

4.EEPROM (electrically erasable and programmable).

The function and use mode are the same as EPROM, but the difference is the data clearing mode, which is cleared with a voltage of about 20V. In addition, it can also use electrical signals to write data. This ROM memory is mainly used for Plug and Play (PnP) interface.

5. Flash memory (flash memory)

This is a kind of memory that can directly modify the contents of the motherboard without unplugging IC. When the power is turned off, the data stored in it will not be lost. When writing data, the original data must be cleared before writing new data. The disadvantage is that the speed of writing data is too slow.