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In a computer system, a blitter (from BLIT or Block Image Transfer) is a co-processor or logic block dedicated to memory data transfers, usually independently of the CPU, using bit blit methods.

In early computers with raster-graphics output, the computer's CPU had the task of moving bitmaps around in memory. But as graphics operations became more intensively used, this work tied down the computer, taking valuable CPU resource away from other tasks.

Computer manufacturers introduced blitters to help lessen the graphics burden on the CPU. For some time in the 1980s several home computers included a graphics co-processor for this task. The CPU would send the bit blit operations to the blitter, which would then carry out the operation much faster than the CPU could.

The Commodore Amiga became one of the first personal computers to use this solution. The first US patent filing to use the term blitter was "Personal computer apparatus for block transfer of bit-mapped image data," assigned to CommodoreAmiga, Inc. On top of the ability to copy and manipulate large areas of graphics, the Amiga's blitter also included line drawing and area-filling hardware.

Later models of the Atari ST also included a blitter co-processor. One story goes that manufacturing delays deferred its introduction into the ST line until after the first STs had shipped. Another is that the Atari ST's main competitor, the Amiga, was famous for its blitter, and so Atari introduced one. Although Atari planned an upgrade to allow dealers to install the blitter chip, this plan was later dropped. The Atari Mega 2 and up (except the Atari TT) had a blitter chip.

Graphics-oriented software (mostly games) running on systems that did not have a blitter needed to find other methods of transferring large graphics. This also applied to cross-platform software that could not rely on the presence of a blitter, but, for whatever reason, was not optimised for the features of each platform.

One approach to handling this, on MC68000 processors at least, involved loading all available processor registers with data from memory, and then putting them back into memory in as few operations as possible. One Bitmap Brothers game, at least, used instructions for stack pushing and popping to accomplish this.