Random-access memory
Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the same amount of time irrespective of the physical location of data inside the memory, in contrast with other direct-access data storage media (such as hard disks, CD-RWs, DVD-RWs and the older magnetic tapes and drum memory), where the time required to read and write data items varies significantly depending on their physical locations on the recording medium, due to mechanical limitations such as media rotation speeds and arm movement.

RAM contains multiplexing and demultiplexing circuitry, to connect the data lines to the addressed storage for reading or writing the entry. Usually more than one bit of storage is accessed by the same address, and RAM devices often have multiple data lines and are said to be "8-bit" or "16-bit", etc. devices.

In today's technology, random-access memory takes the form of integrated circuit (IC) chips with MOS (metal-oxide-semiconductor) memory cells. RAM is normally associated with volatile types of memory (such as dynamic random-access memory (DRAM) modules), where stored information is lost if power is removed, although non-volatile RAM has also been developed. Other types of non-volatile memories exist that allow random access for read operations, but either do not allow write operations or have other kinds of limitations on them. These include most types of ROM and a type of flash memory called "NOR-Flash".

The two main types of volatile random-access semiconductor memory are static random-access memory (SRAM) and dynamic random-access memory (DRAM). Commercial uses of semiconductor RAM date back to 1965, when IBM introduced the SP95 SRAM chip for their System/360 Model 95 computer, and Toshiba used DRAM memory cells for its Toscal BC-1411 electronic calculator, both based on bipolar transistors. Commercial MOS memory, based on MOS transistors, was developed in the late 1960s, and has since been the basis for all commercial semiconductor memory. The first commercial DRAM IC chip, the Intel 1103, was introduced in October 1970. Synchronous dynamic random-access memory (SDRAM) later debuted with the Samsung KM48SL2000 chip in 1992.
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computer memory
Concept
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data
Concept
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machine code
Concept
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random-access
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data
Concept
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Concept
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hard disk
Concept
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CD-RW
MISC
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DVD-RW
Concept
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magnetic tapes
Concept
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drum memory
Concept
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Concept
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Concept
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dynamic random-access memory
Concept
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MISC
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non-volatile memories
Concept
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ROM
Concept
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flash memory
Concept
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NOR-Flash
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semiconductor memory
Concept
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static random-access memory
Concept
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System/360 Model 95
Concept
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Toshiba
ORG
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electronic calculator
Concept
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bipolar transistor
Concept
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MOS transistor
MISC
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Intel 1103
MISC
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Synchronous dynamic random-access memory
Concept
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Samsung
ORG
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Random-access memory
Concept
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