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Blitter
In a computer system, a blitter is a circuit, sometimes as a coprocessor or a logic block on a microprocessor, that is dedicated to the rapid movement and modification of data within that computer's memory. A blitter is capable of copying large quantities of data from one memory area to another relatively quickly, and in parallel with the CPU, while freeing up the CPU's more complex ISA for more general operations.
The name comes from BLIT, which is not an acronym but is often interpreted as BLock Image Transfer. A typical use for a blitter is the movement of a bitmap, such as windows and fonts in a graphical user interface or sprites and backgrounds in a 2D computer game.
==The historical need for a blitter==
In early computers with raster-graphics output, the screen buffer was normally held in main memory and updated using software running on the CPU. For many simple graphics routines, like sprite support or flood filling polygons, large amounts of memory had to be manipulated, and many CPU cycles were spent fetching and decoding instructions for repetitive loops of simple shift/masking operations. For CPUs without caches, this bus requirement for instructions was as significant as data.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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