Memory is used to run programmes, and fast memory speed, expressed in megahertz helps to keep a computer running smoothly. Typically the motherboard of a PC will have a pair of slots for memory. If only one is in use, fitting matched memory with the same speed will boost the performance of the PC. Technical specifications for a PC can be located on the website belonging to the manufacturer the PC. The manual will state the speed of the RAM.

DDR SDRAM Chips and modules
Standard nameModule nameMemory clock
DDR-200PC-1600100 MHz
DDR-266PC-2100133 MHz
DDR-300PC-2400150 MHz
DDR-333PC-2700166 MHz
DDR-400PC-3200200 MHz

Amazon Books
Image of Core Memory: A Visual Survey of Vintage Computers
Author: John Alderman
Publisher: Chronicle Books (2007)
Binding: Hardcover, 160 pages