General Information about Computer Memory (RAM)

There are many different types of memory and this page is by no means a complete dissertation on the various types of memory you will find in computers or printers. For more detailed information, Kingston Technologies has a lot of very good information. I use their site to lookup which memory is needed for a specific device.

Adding Memory to a Computer

The first thing is to lookup what memory has been tested for the computer on the manufacturer’s website. If that cannot be found Kingston has a memory lookup tool that covers most computer’s memory configuration.

When adding memory to a computer all of the memory needs to be the same speed (i.e. PC133, PC3200, etc...) and have the same CL number (Column Access Strobe Latency i.e. CL2, CL3, etc...) or the computer will be unstable.

Double Data Rate (DDR) Memory

Electronic circuits typically perform one transfer per full cycle (rise and fall) of a clock signal. However, this requires that the clock signal changes twice per transfer information to memory, while the data lines change at most once per transfer. DDR transfers data on both the rising and falling edges of the clock signal. By using both edges of the clock the memory can operate at the same frequency as the data signals.

DDR Memory Naming Conventions

DDR 184-pin DIMM DDR2 240-pin DIMM
DDR 200MHz PC-1600 400MHz DDR2 PC2-3200
DDR 266MHz PC-2100 533MHz DDR2 PC2-4200
DDR 333MHz PC-2700 667MHz DDR2 PC2-5300
DDR 400MHz PC-3200 800MHz DDR2 PC2-6400
    1066MHz DDR2 PC2-8500
DDR3 240-pin DIMM DDR4 288-pin DIMM
DDR3 800MT/s PC3-6400 DDR4 1600MT/s PC4-12800
DDR3 1066MT/s PC3-8500 DDR4 1866MT/s PC4-14900
DDR3 1333MT/s PC3-10600 DDR4 2133MT/s PC4-17000
DDR3 1600MT/s PC3-12800 DDR4 2400MT/s PC4-19200
DDR3 1866MT/s PC3-14900 DDR4 2666MT/s PC4-21300
DDR3 2133MT/s PC3-17000 DDR4 2933MT/s PC4-23466
    DDR4 3200MT/s PC4-25600
DDR5 288-pin DIMM  
DDR5 3200MT/s      
DDR5 4000MT/s      
DDR5 4400MT/s      
DDR5 4800MT/s PC5-4800    
DDR5 5200MT/s      
DDR5 5600MT/s      
DDR5 6000MT/s      
DDR5 6400MT/s      

MT/s denotes million transfers per second and represents the effective data rate of DDR SDRAM memory.

Identifying Older Memory

The first step in determining what type of memory your system uses is by looking for a manufacturer's part number. The better memory manufacturers will normally attach a label to the memory stick. If there is no label and you have no clue what type of memory you have you can start by measuring the length of the memory.

Physical 30-Pin SIMM, 72-Pin SIMM, and 168-Pin DIMM Sizes


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