multiprocessing

—multiprocessor, n.

/mul"tee pros'es ing, -euh sing/ or, esp. Brit., /-proh'ses ing, -seuh sing/, n. Computers.

the simultaneous execution of two or more programs or instruction sequences by separate CPUs under integrated control.

[1930-35; MULTI- + PROCESS + -ING¹]

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Mode of computer operation in which two or more processors (see CPU) are connected and are active at the same time.

In such a system, each processor is executing a different program or set of instructions, thus increasing computation speed over a system that has only one processor (which means only one program can be executed at a time). Because the processors must sometimes access the same resource (as when two processors must write to the same disk), a system program called the task manager has to coordinate the processors' activities.

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▪ computing

      in computing, a mode of operation in which two or more processors in a computer simultaneously process two or more different portions of the same program (set of instructions). Multiprocessing is typically carried out by two or more microprocessors (microprocessor), each of which is in effect a central processing unit (CPU) on a single tiny chip. Supercomputers (supercomputer) typically combine thousands of such microprocessors to interpret and execute instructions.

      The primary advantage of a multiprocessor computer is speed, and thus the ability to manage larger amounts of information. Because each processor in such a system is assigned to perform a specific function, it can perform its task, pass the instruction set on to the next processor, and begin working on a new set of instructions. For example, different processors may be used to manage memory storage, data communications, or arithmetic functions. Or a larger processor might utilize “slave” processors to conduct miscellaneous housekeeping duties, such as memory management. Multiprocessor systems first appeared in large computers known as mainframes, before their costs declined enough to warrant inclusion in personal computers (personal computer) (PCs).

      Personal computers had long relied on increasing clock speeds, measured in megahertz (MHz) or gigahertz (GHz), which correlates to the number of computations the CPU calculates per second, in order to handle ever more complex tasks. But as gains in clock speed became difficult to sustain, in part because of overheating in the microprocessor circuitry, another approach developed in which specialized processors were used for tasks such as video display. These video processors typically come on modular units known as video cards, or graphic accelerator cards. The best cards, which are needed to play the most graphic-intensive electronic games (electronic game) on personal computers, often cost more than a bargain PC. The commercial demands for ever better cards to run ever more realistic games, on PCs and video game systems, led IBM (International Business Machines Corporation) to develop a multiprocessor microchip, known as the Cell Broadband Engine, for use in the Sony (Sony Corporation) Computer Entertainment PlayStation 3 and a new supercomputer that included thousands of the microchips.

      It must be noted, however, that simply adding more processors does not guarantee significant gains in computing power; computer program problems remain. While programmers and computer programming languages (computer programming language) have developed some proficiency in allocating executions among a small number of processors, parsing instructions beyond two to eight processors is impracticable for all but the most repetitive tasks. (Fortunately, many of the typical supercomputer scientific applications involve applying exactly the same formula or computation to a vast array of data, which is a difficult but tractable problem.)

      IBM led one effort to address the problem of programming multiprocessor computers through an open source initiative, in which academics, nonprofit organizations, and other corporations contributed advancements. Similar proprietary research was pursued by Microsoft Corporation and Apple Inc.

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