In order understand memory upgrade, it is important to know the different types of memory available. It is possible to have more than one type of memory in a single computer. There are basically 5 memory modules; SIMM, DIMM, SODIMM, RDRAM and SO RIMM. Each of these modules works differently. The Single In-line Memory Modules (SIMMs) are fixed onto a PCB and store one row of DRAM, BEDO or EDO. The largest SIMM currently have 72 pins. A single SIMM can have several chips and by adding more SIMMs, you increase the memory. They are commonly used in desktops.

Dual In-line Memory Modules (DIMMs) are larger with 168 pins and twice as much memory. They have 2 rows of DRAM, BEDO or EDO. Small Outline DIMMs (SODIMMs) are smaller than DIMMs, with either 72 pins or 144 pins. They are mostly used in notebooks. SO RIMMs are near similar to SODIMM but differ in technology. RDRAM – RIMMs are the latest modules with up to 184 pins transferring 1.6 GB per second in 16 bits. With increase in chip speed, there is faster access to memory. There is also custom USB memory where data can be accessed in case the machine crashes.