Computer storage technology
Mata-Toledo, Ramon A. Department of Computer Science, James Madison University, Harrisonburg, Virginia.
Gupta, Pranshu Department of Mathematics and Computer Science, DeSales University, Center Valley, Pennsylvania.
Last reviewed:April 2018
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- Computer storage technology, published July 2016:Download PDF Get Adobe Acrobat Reader
- Computer storage technology, published June 2014:Download PDF Get Adobe Acrobat Reader
- Characteristics of storage
- Memory hierarchy
- Primary storage
- Secondary storage
- Tertiary storage
- Offline storage
- Enterprise-level storage
- Links to Primary Literature
- Additional Readings
The hardware components, both internal and external, of a computer used to read (retrieve) or write (save) digital data. The ability to read and write data is an essential function of a computer and of the so-called von Neumann architecture (stored-program computer) on which most computers are based. In computers, the central processing unit (CPU or the processor) is the electronic component that carries out the instructions of a program. The CPU performs the arithmetic, logical, control, and input/output (I/O) operations specified by a program stored in main memory. The data itself can be stored in main memory or in some external device. Modern computers may have a large amount of main memory, sometimes on the order of terabytes (1012 bytes). A byte (eight bits or binary digits) is the basic memory unit of the computer. A bit can only hold a single value of 0 or 1. However, there are still applications for which even that amount of memory is not enough. In early computer systems, memory technology was very limited in speed and size and was very expensive; for example, around 1978, 512 kilobytes cost about U.S. $100,000. A kilobyte is equivalent to 1024 bytes. The word kilo, which generally means 1000, is used here as 1024, because bytes and all multiples are powers of 2 (210 = 1024). Since the mid-1980s, the advent of high-density, high-speed, random-access memory (RAM) chips has reduced the cost of memory by more than two orders of magnitude. Memory chips now are no larger than 6 mm2 and contain all the essential hardware to store thousands of bits of data or instructions (Fig. 1). See also: Bit; Computer; Computer architecture; Computer programming; Digital computer; Numerical representation (computers)
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