Random Access Memory
Random Access Memory (more commonly, RAM) is a term most often used to describe the main system memory of an electronic computer. There have been many types of memory devices called "RAM", most of which share the common features of having read\write access to any nonsequential memory location (thus "random" access), and relatively fast data access times.
The most common type of RAM used in personal computers is Dynamic Random Access Memory (DRAM) patented in 1968 by Robert Dennard at IBM. During the 1990's Synchronous DRAM (SDRAM) became the most common type of DRAM used in computers. SDRAM is most commonly found on Pentium II and Pentium III computers owing to its 100 and 133 MHz operating speeds. Newer types of SDRAM include "Double Data Rate" types DDR, DDR2, and (naturally) DDR3 SDRAM. All newer types of SDRAM chips (see integrated circuits designed for use as main system memory on a personal computer come mounted on some type of module (SIMM, DIMM, etc) that is designed to plug directly into the computers motherboard, typically very near the processor.
Other types of RAM have included Static RAM (SRAM), the type used in the cache inside the processor, and Non-Volatile RAM (NVRAM). It is important to note here that most types of RAM are volatile, meaning that if power is removed, the information stored will be lost, and also that this list of types is by no means exhaustive.
The newest form of memory, Rambus DRAM (RDRAM) was developed by Rambus Corporation. When it first came out in 1999, it offered clock speed of 800MHz and transfer rates of up to 1.6Gbps. Although it offers higher performance than its predecessors, it has not gained market popularity because is still quite expensive and has some motherboard compatibility issues. As of now it also available at clock speeds of 1066, and 1200MHz.
In some sense, Flash memory can be considered RAM, as it is randomly addressable, although it is typically not as fast as other RAM technologies. ROM, EPROM, and EEPROM could also be considered "random access" types of memory by this reasoning, although this is not generally the nomenclature conventionally used.
- rambus.com. RDRAM® Frequently Asked Questions.