DSQC639 3HAC025097-001/14A Main computer ABB

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Essential details：DSQC639 3HAC025097-001/14A Main computer ABB

Main memory (Main memory), short for main memory. Is an important part of computer hardware, its role is to store instructions and data, and can be directly random access by the central processing unit (CPU). In order to improve the performance, modern computer can take into account the reasonable cost, often adopt multilevel storage system. In other words, the main memory with small storage capacity and high access speed is essential. Main memory stores information by address, and access speed is generally independent of address. 32-bit (bit) addresses can represent up to 4GB of memory addresses. This is sufficient for most applications, but it is not enough for some applications with very large amounts of computation and very large databases, which raises the need for 64-bit structures.

DSQC639

The main memory generally adopts semiconductor memory, which has the characteristics of small capacity, fast reading and writing speed and high price compared with auxiliary memory. The main memory in the computer is mainly composed of five parts: the memory, the control line, the address register, the data register and the address decoding circuit.
Since 1970s, the main memory has been gradually composed of large-scale integrated circuits. The most commonly used and most economical are dynamic random access memory chips (DRAM). In 1995, DRAM chips with an integration capacity of 64Mb (capable of storing 4 million Chinese characters) began to be commercially produced, and 16MbDRAM chips have become the mainstream products in the market. The access speed of DRAM chips is moderate, usually 50 to 70ns. Some improved DRams, such as EDO DRams (extended data output DRams), can improve their performance by more than 10 percent over ordinary DRams, and SDRams (synchronous DRams) can improve their performance by about 10 percent over EDO DRams. In 1998, SDRAM II (or DDR, double data rate), the successor of SDRAM, was launched. In the pursuit of speed and reliability, usually the expensive static random access memory chip (SRAM), its access speed can reach 1~15ns. Regardless of whether the main memory is made of DRAM or SRAM chips, information stored in a power outage is “lost”, so computer designers should consider maintaining power for a few milliseconds to preserve important information in main memory so that the computer can resume normal operation when power is restored. In view of the above situation, in some applications, the main memory to store important and relatively fixed programs and data is composed of “non-volatile” memory chips (such as EPROM, flash memory chips, etc.); For completely fixed programs, the data area is even composed of read-only memory (ROM) chips; These parts of the main memory are protected from temporary power outages and from viruses.

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