RapidCAD
Encyclopedia
RapidCAD is a specially packaged Intel 486DX and a dummy floating point unit
(FPU) designed as pin-compatible replacements for an Intel 80386
processor and 80387 FPU. Because the i486DX has a working on-chip FPU, a dummy FPU package is supplied to go in the Intel 387 FPU socket. 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 1 cache and the bottleneck of the 386 bus. RapidCAD offers minimal improvement in integer performance over a 386DX (typically 10%, at most 35%), but provides substantial improvement in floating point operations (up to 80% faster) for which it was marketed. Floating point performance is mostly improved by moving the FPU onto the CPU core.
Intel RapidCAD-2
Floating point unit
A floating-point unit is a part of a computer system specially designed to carry out operations on floating point numbers. Typical operations are addition, subtraction, multiplication, division, and square root...
(FPU) designed as pin-compatible replacements for an Intel 80386
Intel 80386
The Intel 80386, also known as the i386, or just 386, was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit of many workstations and high-end personal computers of the time...
processor and 80387 FPU. Because the i486DX has a working on-chip FPU, a dummy FPU package is supplied to go in the Intel 387 FPU socket. 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 1 cache and the bottleneck of the 386 bus. RapidCAD offers minimal improvement in integer performance over a 386DX (typically 10%, at most 35%), but provides substantial improvement in floating point operations (up to 80% faster) for which it was marketed. Floating point performance is mostly improved by moving the FPU onto the CPU core.
Technical specifications
Intel RapidCAD-1- Package: 132-Pin CPGA
- CPU clock: 25/33 MHz
- Transistors: 800,000
- Process: CHMOS 0.8µm
- Voltage: 5V
- sSpec: SZ624
Intel RapidCAD-2
- Package: 68-Pin CPGA
- CPU clock: 25/33 MHz
- Transistors: 275,000
- Process: CHMOS
- Voltage: 5V
- sSpec: SZ625