Storage device (ii)

Overview

When accessing a storage unit according to the address in Mar, address decoding, driving, etc. are required to find the unit to be accessed. The readout also passes through the readout amplifier to send the stored word of the selected unit to the MDR. When writing, the data in the MDR must also be written to the circuit in order to actually write to the selected unit.

Main memory structure

The main memory chip and CPU are connected by bus, Mar and MDR are made in the CPU chip.

When a word is to be read from the memory, the CPU first sends the address of the word to mar, passes address bus to main memory, and then issues a read command. Main memory after receiving the read command, the need to know the contents of the address unit, after the completion of the read operation, the contents of the unit read to the data line bus, where the information is sent to where the MDR, is determined by the CPU.

If a word is to be saved, the CPU will first send the address of the main cell of the word to the address line via Mar, and then send the information to the MDR, sending a write command to primary memory, and after receiving the write command, the information on the data line will be written to the corresponding address line indicated by the main deposit cell.

Allocation of address of storage unit in storage

A 8-bit binary number represents a byte, and the stored word length is a multiple of 8. Computer systems can be addressed by word or by byte.

Main Memory Technical Index

Storage capacity

Storage capacity = Number of storage units * Storage length

Storage capacity in bytes = Number of memory units * Storage Word length/8

Storage speed

Access time refers to the time it takes to start a memory operation to complete the operation.

The access period is the minimum interval required for the memory to perform two separate memory operations at a time.

Bandwidth of the storage device

Amount of information in memory storage period per unit of time, units available words per second, bytes per second

Storage device (ii)