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Concept
Coprocesseur
Résumé
A coprocessor is a computer processor used to supplement the functions of the primary processor (the CPU). Operations performed by the coprocessor may be floating-point arithmetic, graphics, signal processing, string processing, cryptography or I/O interfacing with peripheral devices. By offloading processor-intensive tasks from the main processor, coprocessors can accelerate system performance. Coprocessors allow a line of computers to be customized, so that customers who do not need the extra performance do not need to pay for it.
Coprocessors vary in their degree of autonomy. Some (such as FPUs) rely on direct control via coprocessor instructions, embedded in the CPU's instruction stream. Others are independent processors in their own right, capable of working asynchronously; they are still not optimized for general-purpose code, or they are incapable of it due to a limited instruction set focused on accelerating specific tasks. It is common for these to be driven by direct memory access (DMA), with the host processor (a CPU) building a command list. The PlayStation 2's Emotion Engine contained an unusual DSP-like SIMD vector unit capable of both modes of operation.
To make the best use of mainframe computer processor time, input/output tasks were delegated to separate systems called Channel I/O. The mainframe would not require any I/O processing at all, instead would just set parameters for an input or output operation and then signal the channel processor to carry out the whole of the operation. By dedicating relatively simple sub-processors to handle time-consuming I/O formatting and processing, overall system performance was improved.
Coprocessors for floating-point arithmetic first appeared in desktop computers in the 1970s and became common throughout the 1980s and into the early 1990s. Early 8-bit and 16-bit processors used software to carry out floating-point arithmetic operations. Where a coprocessor was supported, floating-point calculations could be carried out many times faster.
Source officielle
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