Weitek 4167 is a high-performance Floating Point Unit for
Intel 80486 family of microprocessors.
The 4167 works similar to Weitek 3167 FPU,
and offers much better performance (3 - 4 times faster by some estimates)
than the 3167. To communicate with the Weitek 4167 the CPU reads
from/writes to memory space designated for the FPU. This communication
method was beneficial to previous generation of Weitek 3167 FPUs
because it was faster than I/O communication method used by
80387 co-processors. On 4167 this
communication method became one of FPU disadvantages due to changes in
80486 CPU architecture. In 80486 family the co-processor was
integrated with the main processor, thus eliminating communication
delay between the CPU and FPU. Other disadvantages of the Weitek 4167
were the same as for the 3167 FPU:
- The 4167 FPU didn't fit into 80486 upgrade socket and required a
separate 142-pin socket to be present on the motherboard.
- The Weitek FPU instruction set was different from 80x87 instruction
set. All applications compiled for 487 FPU didn't work with the 4167
co-processor. To take advantage of the 4167 FPU the applications had
to be re-compiled using a compiler which supported Weitek
co-processor.
The 4167 offered better performance than integrated FPU in the 80487
and 80486DX processors, but it lost its performance lead with the
introduction of 80486DX2 CPUs.
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