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Last updated on April 19, 2014 at 1:20 EDT

Random Access Memory

Random access memory (RAM) is a form of computer data storage that takes the form of integrated circuits in order to allow stored data to be accessed in any order. Random refers to the idea that any piece of data can be restored in a constant time, regardless of its physical location and whether or not it is related to the prior piece of data. The word RAM is often associated with unstable types of memory where the information is lost after the power is switched off.

Magnetic core memory was introduced in 1949 as an early type of widespread writable random-access memory. Later, it was used in most computers up until the development of static and dynamic integrated RAM circuits in the 1970s. Today, types of writable RAM store data in either the state of a flip-flop, as in static RAM, or as a charge in a capacitor, as in dynamic RAM. Some types have circuitry to detect and fix random memory errors in the stored data by using similar bits or error correction codes. The read-only type of RAM, called ROM, uses a metal mask to permanently enable or disable selected transistors. SRAM and DRAM are other volatile forms of computer storage that have been used as constant storage in traditional computers. Newer products, however, rely on flash memory to preserve data when it is not being used. Some personal computers also have replaced magnetic disks with flash drives.

Most computer systems have a memory hierarchy that consists of CPU registers, on-die SRAM caches, external caches, DRAM, paging systems, and virtual memory on a hard drive. This whole collection of memory is considered RAM. The purpose of using a memory hierarchy is to acquire the highest possible average access performance while reducing the total cost of the entire memory system. Also, most computers come with RAM that is in an easily upgraded form of modules called memory modules. They can be replaced easily if they become damaged.

Recent developments involve several new types of non-volatile RAM that will preserve data while it’s turned off. Engineers are hopeful that these new technologies will be able to revolutionize RAM. Since 2006, solid-state drives with larger capacities and exceptional performance have become available.

Random Access Memory