Weitek 3167 coprocessors
The 3167 was introduced by Weitek in 1989 and provided the fastest floating-point performance possible on a 386 based system at that time. The 3167 is not a real coprocessor, strictly speaking, but rather a memory-mapped peripheral device. The architecture of the 3167 was optimized for speed wherever possible. Besides using the faster memory mapped interface to the CPU (the 80x87 uses IO-ports), it does not support many of the features of the 80x87 coprocessors, allowing all of the chip's resources to be concentrated on the fast execution of the basic arithmetic operations.
In benchmark comparisons, the Weitek 3167 provided up to 2.5 times the performance of an Intel 387DX coprocessor. For example, on a 33MHz 3167 the Whetstone benchmark performed at 7574 kWhetstones/sec compared with the 3743 kWhetstones/s for the Intel 387DX. Note, however, that these are single-precision results and that the Weitek 3167's performance would drop to about half the stated rate for double-precision, while the value for the Intel 387DX would change very little. In any case, before the advent of the Intel RapidCAD, the Weitek 3167 usually outperformed all 387-compatible coprocessors, even for double-precision operations. For typical applications, the advantage of the Weitek 3167 over the 387 clones is much smaller. In a benchmark test using AutoDesk's 3D-Studio the Weitek 3167 performed at 123% of the Intel 387DX's performance compared with 106% for the Cyrix FasMath 83D87 and 118% for the Intel RapidCAD.
The Weitek Abacus 3167 is packaged in a 121-pin PGA that fits into an EMC socket (provided in most 386-based systems). It does not fit into the normal 68-pin PGA socket intended for a 387 coprocessor.
To get the best of both worlds, one might want to use a Weitek 3167 and a 387 compatible coprocessor in the same system. These coprocessors can coexist in the same system without problems; however, most 386-based systems contain only one coprocessor socket, usually of the EMC (extended math coprocessor) type. Thus, you can install either a 387 coprocessor or a Weitek 3167, but not both at the same time. There are small daughter boards available that plug into the EMC socket and provide two sockets, an EMC and a standard coprocessor socket.