The IIT chip 3C87 was introduced in 1989, about the same time as the Cyrix 83D87. Both coprocessors are faster than Intel’s 387DX coprocessor. The IIT 3C87 also provides extra functions not available on any other 387 chip. It has 24 user-accessible floating-point registers organized into three register banks. Three additional instructions (FSBP0, FSBP1, FSBP2) allow switching from one bank to another. The register bank’s main purpose is to aid the fourth additional instruction the 3C87 has (F4X4), which does a full multiply of a 4×4 matrix by a 4×1 vector, an operation common in 3D-graphics applications. There are very few applications that make use of it when an IIT coprocessor is detected at run time (among them Silver Screen and Fast-CAD 3-D).
The 3C87 is implemented in an advanced CMOS process and has low power requirements, typically about 600 mW. Like the 387 ‘clones’ from Cyrix and ULSI, the 3C87 does not support asynchronous operation of the CPU and the coprocessor, but always runs at the full speed of the CPU. It is available in 16, 20, 25, 33, and 40 MHz versions.
|Core Frequency:||25 MHz|
|Board Frequency:||25 MHz|
|Data bus (ext.):||32 Bit|
|Address bus:||32 Bit|