A freakshow of a processor. Developed in the late 80's in response to the RISC revolution. The i860 can best be described as it was advertised, a supercomputer on a chip. This makes for great advertising, but not for a good general purpose microprocessor. The i860 was fast (in fact, faster than the Pentiums that were designed after it), but like all supercomputers, was quirky. It couldn't achieve full speed with conventional compilers, and for full speed, needed to be coded in assembly (carefully). It had perversely long interrupt latencies, on the order of 1000 cycles (you read that right). It also had a built in graphics accelerator (you read that right) that could do Gouraud shading, texturing, and z-buffering. It is for these reasons that the i860 ended up in graphics cards. It was also used as a floating point accelerator because of its vector abilities, a distinct mark of the supercomputers. Of course, it was in the Intel Paragon supercomputers (although a i386 version of the Paragons did exist).

The i860 was some perverse mix of a 64 bit processor and a 32 bit processor. Address was 32 bits, as were instructions. However, operations could be, in most cases, performed on 32 bit or 64 bit operands. In fact, the register set is described being either 64 32 bit registers, or 32 64 bit registers. It has various vector operations that it can perform (floating point and otherwise). It can use the 8K cache in some circumstances as a vector register, like many supercomputers. It has a superscalar mode, where it can dispatch three instructions to its four pipes simultaniously. The pipelines are user visible (an oddity), that allowed for a particularly heinous programming trick, where bogus operands were stuffed into the pipes for additional storage (yeilding 192 64 bit register equivalents).

The i860's lasting legacy is in various parts of other Intel processors.

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