Memory is made of a group of RAM chips with each chip packaging a set of memory locations. These chips are mounted onto flat electronic boards that are plugged into a microcomputer’s motherboard. Popular types of these boards are the single inline memory module (SIMM) and the dual inline memory module (DIMM). The memory word size, which is the number of data bits that can be accessed at a time, for DIMM is dual (double) that for SIMM. Memory speed is measured by the time needed to read one memory word. It is expressed in nanoseconds (1 ns = billionth of a second).

Based upon the manufacturing methodology, RAM chips are classified as:

- Dynamic RAM (DRAM): RAM needs to be periodically recharged otherwise memory contents will be lost. During recharging times, RAM cannot be accessed by the CPU.

- Static RAM (SRAM): RAM does not need recharging. Hence, it is faster but more expensive.