RapidCAD is a specially packagedIntel 486DX and a dummyfloating-point unit (FPU) designed as pin-compatible replacements for anIntel 80386 processor and80387 FPU. Because the i486DX has a working on-chip FPU, a dummy FPU package (the "RapidCAD-2") is supplied to go in theIntel 387 FPU socket.[1] The dummy FPU is used to provide the FERR signal, necessary for compatibility purposes.
Despite being able to execute instructions in the same number of cycles as an i486DX, integer performance on RapidCAD suffers due to the absence of level 1cache and the bottleneck of the 386bus. RapidCAD offers minimal improvement in integer performance over a 386DX (typically 10%, at most 35%), but provides substantial improvement infloating-point operations (up to 80% faster) for which it was marketed, primarily forcomputer-aided design (hence the name). Floating-point performance is mostly improved by moving the FPU onto the CPU core. Other source reports that the performance boost ranged from 20 to 170 percent faster than the regular386DX based motherboards. It was available at manufacturer's suggested list price of US$499.[2]
