(Previously "direct-access memory"). A data storage device for which the order of access to different locations does not affect the speed of access. This is in contrast to, say, a magnetic disk, magnetic tape or a mercury delay line where it is very much quicker to access data sequentially because accessing a non-sequential location requires physical movement of the storage medium rather than just electronic switching.
In the 1970s magnetic core memory was used and some old-timers still call RAM "core". The most common form of RAM in use today is semiconductor integrated circuits, which can be either static random-access memory (SRAM) or dynamic random-access memory (DRAM).
The term "RAM" has gained the additional meaning of read-write. Most kinds of semiconductor read-only memory (ROM) are actually "random access" in the above sense but are never referred to as RAM. Furthermore, memory referred to as RAM can usually be read and written equally quickly (approximately), in contrast to the various kinds of programmable read-only memory. Finally, RAM is usually volatile though non-volatile random-access memory is also used.
Interestingly, some DRAM devices are not truly random access because various kinds of "page mode" or "column mode" mean that sequential access is faster than random access.
The humorous expansion "Rarely Adequate Memory" refers to the fact that programs and data always seem to expand to fill the memory available.
Hardware inside your computer that retains memory on a short-term basis and stores information while you work. RAM is one of the things that make your computer run faster. It comes in 32-bit, 64-bit, 128-bit, 256-bit, and higher, and you can add additional "blocks" of RAM, depending on your computer.
Slang usage of this term often describes someone who does not possess the mental capacities required for the task at hand, as in, "I wouldn't ask him to do it, he's a little short on RAM." Actual RAM comes in a variety of forms: DRAM (Dynamic Random-Access Memory): A memory chip contained on such devices as video and sound cards.
A type of data storage device which is manufactured with fixed contents. In its most general sense, the term might be used for any storage system whose contents cannot be altered, such as a gramophone record or a printed book; however, the term is most often applied to semiconductor integrated circuit memories, of which there are several types, and CD-ROM.
ROM is inherently non-volatile storage - it retains its contents even when the power is switched off, in contrast to RAM.
ROM is often used to hold programs for embedded systems since these usually have a fixed purpose. ROM is also used for storage of the lowest level bootstrap software (firmware) in a computer.
Built-in computer memory that can be read but not written to. ROM contains the programming that allows your computer to boot up each time you turn it on, and it contains essential system programs that neither you or the computer can erase. Unlike a computer's random access memory (RAM), ROM does not lose its data when the computer power is turned off. It is sustained by a small, long-life battery. (If you ever run the hardware setup procedure on your computer, you are in effect writing to ROM.)
ROM can also refer to Rough Order of Magnitude, referring to the amount of time it takes to accomplish a given task.
The BIOS of a mother board is made of ROM.