Wednesday, June 19, 2013


To make 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 co-processor was supported, floating-point calculations could be carried out many times faster. Math co-processors were popular purchases for users of computer-aided design (CAD) software and scientific and engineering calculations. Some floating-point units, such as the AMD 9511, Intel I8231 and Weitek FPUs were treated as peripheral devices, while others such as the Intel 8087, Motorola 68881 and National 32081 were more closely integrated with the CPU.

Another form of co-processor was a video display coprocessor, as used in the Atari 8-bit family, the Texas Instruments TI-99/4A and MSX home-computers, which were called "Video Display Controllers". The graphics processor chip in the Commodore Amiga series was known as the "Copper".

As microprocessors developed, the cost of integrating the floating point arithmetic functions into the processor declined. High processor speeds also made a closely integrated coprocessor difficult to implement. Separately packaged mathematics co-processors are now uncommon in desktop computers. The demand for a dedicated graphics co-processor has grown, however, particularly due to an increasing demand for realistic 3D graphics in computer games.

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