Digital Life

Memory of machines

Silicon chips form the essence of every computer, from microprocessors that perform logic functions on data to the memory modules that store the information. Here's a look at the most common forms of memory:

Random Access Memory, or RAM, chips, used to store programs and data being processed, are the most common chips inside computers. Unlike some types of memory, they can be read and written. But the information they keep lasts only as long as power is supplied to the system. Still, RAM chips are fast and cheap. RAM is available in two main types, static and dynamic.

Static RAM, or SRAM, is by far the fastest and is typically used as a memory cache inside microprocessors. Unlike dynamic RAM, It stores information without requiring constant power refreshes. It is, however, several times more expensive than DRAM.

Dynamic RAM, or DRAM, the most common form of RAM, also stores information as long as power is supplied to the circuit. To maintain the data, it must be refreshed several hundred times each second. DRAM is available in many varieties, each known by dizzying acronyms. Extended Data Output DRAM is faster than conventional DRAM. EDO DRAM has now been surpassed by Synchronous DRAM, which runs about twice as fast. The newest computers also support Double Data Rate SDRAM, or DDR SDRAM, which also consumes less power.

RDRAM is a DRAM developed by Rambus Inc. RDRAM that is very fast but more expensive than DRAM. It was the only supported DRAM for Intel Corp.'s Pentium 4 in the first several months after the processor's release. Newer Pentium 4 chip sets support less expensive but slower forms of memory, such as DDR SDRAM.

Read Only Memory chips, or ROMs, are much slower than Random Access Memory but continue to store information even after power has been shut off. The Basic Input-Output System, or BIOS, a program that loads into a computer each time it is turned on, is stored on such a chip.

Programmable ROM chips, or PROMs, can be written to. A very popular form of ROM memory called flash memory is found in popular electronic consumer gadgets such as cell phones, digital cameras and digital music players. The chips store phone numbers, pictures and songs even if the power has been cut off.

- Associated Press

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