Classic Computer Magazine Archive COMPUTE! ISSUE 89 / OCTOBER 1987 / PAGE 10

What's A Blit?

I've heard people talk about a "blitter" in the Amiga. Just what is a blitter and why is it important?

Jeff Murphy

The word blit is short for bit-block image transfer, so a blitter is something which transfers bit-block images. All the images that are displayed are your screen are represented internally as rectangular groups of bits. The blitter's job is to move the collection of bits that make up a graphics image from one part of memory to another at high speed.

Most computers rely on the microprocessor to perform these transfers. Unfortunately, this slows down the computer to a great degree any time an image needs to be moved. Since the Amiga's blitter operates independently of its 68000 processor, smooth animation is possible.

If your favorite language is C, Modula-2, or machine language, you can access the blitter directly, creating blazing animation. If you program in Amiga Basic, you can still use the blitter. Amiga Basic has OBJECT commands which control bobs (blitter objects).

Right now, the Amiga is the only personal computer that has a blitter, but during the past year Atari has been showing one for its ST line of computers. As of this writing (early July), it is rumored that production problems may keep the blitter from being shipped in the new Mega ST line of computers. Presumably, the blitter will be made available as an upgrade to both the Mega series and the 520 and 1040STs. The older machines will also need new ROM chips to support the blitter.