Intel I860 - Versions and Applications

Versions and Applications

The chip was released in two versions, the basic XR (code named N10), and the XP (code named N11). The XP added larger on-chip caches, a second level cache, faster buses, and hardware support for bus snooping, for cache consistency in parallel computing systems. The XR ran at 25 or 40 MHz, and a process shrink for the XP (from 1 micrometre to 0.8) bumped the XR to 40 and 50 MHz. Both ran the same instruction set.

At first the i860 was only used in a small number of very large machines like the iPSC/860 at Los Alamos National Laboratory. As the compilers improved, the general performance of the i860 did likewise, but by then most other RISC designs had already passed the i860 in performance.

Intel for a time tested the viability of the i860 as a workstation CPU, competing with the MIPS Architecture chips and others. Microsoft initially developed what was to become Windows NT on internally-designed i860-based workstations (codenamed Dazzle), only porting NT to the MIPS (Microsoft Jazz), Intel 386 and other processors later. The NT designation originally referred to the "N-Ten" (i860 XR) processor.

The i860 did see some use in the workstation world as a graphics accelerator. It was used, for instance, in the NeXTdimension, where it ran a cut-down version of the Mach kernel running a complete PostScript stack. However, the PostScript part of the project was never finished so it ended up just moving color pixels around. In this role the i860 design worked considerably better, as the core program could be loaded into the cache and made entirely "predictable", allowing the compilers to get the ordering right. Truevision produced an i860-based accelerator board intended for use with their Targa and Vista framebuffer cards. Pixar produced a custom version of RenderMan to run on the card that ran approximately 4 times faster than the 386 host. Another example was SGI RealityEngine, which used a number of i860XP processors in its geometry engine. This sort of use slowly disappeared as well, as more general-purpose CPUs started to match the i860's performance, and as Intel turned its focus to Pentium processors for general-purpose computing.

Mercury Computer Systems used the i860 in their multicomputer. From 2 to 360 compute nodes would reside in a circuit switched fat tree network, with each node having local memory that could be mapped by any other node. Each node in this heterogeneous system could be an i860, a PowerPC, or a group of three SHARC DSPs. Good performance was obtained from the i860 by supplying customers with a library of signal processing functions written in assembly language. The hardware packed up to 360 compute nodes in 9U of rack space, making it suitable for mobile applications such as airborne radar processing.

During the early 1990s, Stratus Technologies built i860-based servers, the XA/R series, running their proprietary VOS operating system.

In the late 1990s Intel replaced their entire RISC line with ARM-based designs, known as the XScale. Confusingly, the 860 number has since been re-used for a motherboard control chipset for Intel Xeon (high-end Pentium) systems.