Updated: 04/26/2017 by Computer Hope

Alternatively referred to as main memory, primary memory, or system memory, Random Access Memory (RAM) is a hardware device that allows information to be stored and retrieved on a computer. RAM is usually associated with DRAM, which is a type of memory module. Because information is accessed randomly instead of sequentially like it is on a CD or hard drive, the computer can access the data much faster. However, unlike ROM or the hard drive, RAM is a volatile memory and requires power to keep the data accessible. If the computer is turned off, all data contained in RAM is lost.

Tip: New users often confuse RAM with disk drive space. See our memory definition for a comparison between memory and storage.

Types of RAM

Over the evolution of the computer there have been different variations of RAM. Some of the more common examples are DIMM, RIMM, SIMM, SO-DIMM, and SOO-RIMM. Below is an example image of a 512 MB DIMM computer memory module, a typical piece of RAM found in desktop computers. This memory module would be installed into one of the memory slots on a motherboard.

Computer DIMM or dual-inline memory module

Additional information

As the computer boots, parts of the operating system and drivers are loaded into memory, which allows the CPU to process the instructions faster and speeds up the boot process. After the operating system has loaded, each program you open, such as the browser you're using to view this page, is loaded into memory while it is running. If too many programs are open the computer will swap the data in the memory between the RAM and the hard disk drive.

History of RAM

The first form of RAM came about in 1947 with the use of the Williams tube. It utilized a cathode ray tube (CRT) and data was stored on the face of the CRT as electrically charged spots.

The second widely used form of RAM was magnetic-core memory, invented in 1947. Frederick Viehe is credited with much of the work, having filed for several patents relating to the design. Magnetic-core memory works through the use of tiny metal rings and wires connecting to each ring. One bit of data could be stored per ring and accessed at any time.

However, RAM as we know it today, as solid state memory, was first invented in 1968 by Robert Dennard. Known specifically as dynamic random access memory, or DRAM, transistors were used to store bits of data.

Related pages

DDR, DDR2, DDR3, DDR4, Dynamic storage, Memory terms, Primary storage, RDRAM, SIMM, SDRAM