Blitters

A blitter is a hardware or software component that performs block image transfers and related pixel operations, typically moving rectangular regions of video memory and optionally combining them with other image data. The name derives from bit-block transfer, or blit, a term used to describe moving blocks of bits in memory. Blitters were common in earlier computer systems as dedicated co-processors or as features of display hardware to accelerate graphics tasks while the CPU handled other work.

Functionally, a blitter copies a source rectangle to a destination rectangle in memory and may apply a variety of operations during the transfer. These operations can include raster or logical operations (such as AND, OR, XOR), masking, color keying for transparency, and sometimes color expansion or pixel format conversions. In many designs, the blitter can operate asynchronously from the CPU, enabling smoother animation, scrolling, and compositing of moving sprites or background layers.

Notable examples include the Amiga’s custom blitter, which could perform multiple data fetches and pixel-wise operations in parallel with CPU execution, supporting efficient graphics effects and smooth scrolling. In other architectures, blitting is implemented via DMA engines or as part of the GPU’s rasterization and memory-copy pathways. The concept persists in modern hardware as rectangle transfers and texture blits within GPUs and display pipelines, where efficient memory-to-memory or memory-to-framebuffer transfers are essential for performance.

In summary, blitters accelerate image copying and compositing by handling block transfers and simple raster operations, reducing CPU load and enabling more complex graphics effects in both historical and contemporary systems. See also bit blt, raster operation, and graphics hardware.