November 11, 2020
The speed of the memory bar generally uses the time of accessing data once (the unit is generally ns) as a performance indicator. The shorter the time, the faster the speed. The speed of ordinary memory can only reach 70ns to 80ns, the speed of EDO memory can reach 60ns, and the speed of SDRAM memory has reached 7ns.
Note: There are many manufacturers of memory sticks, and there is no unified labeling specification yet. Therefore, the performance index of the memory cannot be simply read from the memory chip label, but the speed can be understood, such as -70 or -60, etc. The number indicates that the speed of this memory chip is 70ns or 60ns.
There are a variety of specifications for memory module capacity. Early 30-line memory modules have 256K, 1M, 4M, 8M capacities, 72-line EDO memory is mostly 4M, 8M, 16M, and 168-line SDRAM memory is mostly 16M , 32M, 64M, 128MB capacity, or even higher. Figure 5-1 is a unique 64MB memory stick.
3. Parity check
In order to verify the accuracy of the accessed data, each 8-bit capacity in the memory module can be equipped with 1 bit as a parity bit, and the parity check circuit of the main board can be used to correctly verify the accessed data. However, whether there is a parity bit in actual use has no effect on system performance, so currently most memory modules no longer have a check chip installed.
Note: The computer counts in binary, expressed as 0 and 1. When the machine writes data to the memory, it actually stores the code 01, and the parity check counts the number of codes stored in the unit. , And save the statistical results in the parity bit. When the computer fetches the data in the memory, the parity check compares the statistical results with the actual read data to see if they are consistent, thus ensuring the correctness of the memory data .
4. The voltage of the memory
FPM memory and EDO memory both use 5V voltage, while SDRAM uses 3.3V voltage. Please note that the jumper on the motherboard cannot be set wrong during use.
5. Memory clock speed
The memory clock speed represents the highest work efficiency that the memory can achieve. The main frequency of the memory is measured in MHz (Mega Hertz). The higher the memory clock speed, to a certain extent, the faster the memory can reach.
6. Access time TAC
TAC only represents the time required to access the data. The access time is marked with -6 and -5 (-6 means 60ns, -5 means 50ns).
CL (CASLatency) is the delay time of CAS (ColumnAddressStrobe, column address controller). It is an important indicator of memory performance, and it is the response time of memory vertical address pulses.
SPD (Serial Presence Detect, serial presence detection) is an EEPROM chip, which stores the relevant information of the memory stick, such as capacity, chip manufacturer, working speed, whether it has ECC verification and other parameters. When booting, the motherboard BIOS program uses the data in the SPD chip to set the operating parameters of the memory to make it work in the best state and better ensure the stable operation of the system.