Two types of RAM chip

Dynamic (DRAM) - Less expensive to manufacture therefore is most popular. Requires refreshing.
parity, nonparity, ecc

Parity is simple error detection (not correction) If the 9th bit is not what the computer expectes you receive a parity error.

Parity errors usually occur when the chips become unreliable due to age or heat damage.

Static RAM (SRAM) - Holds data until the power is turned off. Very expensive to manufacture.

SIMM - Single Inline Memory Module
30 or 72 pin
8 to 64 mB on one stick

DIMM - Dual Inline Memory Module
168 pin
8 MB to 256 MB

There are other considerations on selecting RAM. For now assume that you simply have to match the RAM type to the motherboard.

DRAM must be refreshed every 3.86 milliseconds.