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Intel RapidCAD - 1989
Intel RapidCAD is the first ever upgrade solution (a predecessor of Intel OverDRIVE line) provided for old PC users (for existing 80386 to be more precise). The 386 PC owners do not need to change their motherboard in their computers; they only need to buy the RapidCAD chips and replace the old CPU in their computer to experience the fast, 486-like, speed. RapidCAD is actually a 80486 die with stripped internal cache in a 80386 package. RapidCAD also does not support the newer 486 specific instructions. Because of the package limitation, the overall performance of RapidCAD installed system is still not as good as upgrading the whole system to 80486 DX. Under the same clock speed, 486 DX is about 2 times faster than a 386/387 system; on the other hand, RapidCAD only has about 37% increase for integer and 70% increase for floating point computation performance.
The interesting thing about Intel RapidCAD is that it is actually a set of two chips. That is because 486 DX has built-in co-processor but 80386 working with a seperate co-processor - 80387. There, RapidCAD-1 has a co-processor itself (because it is based on 486 DX) and do not need a 387. RapidCAD-2 is a dummy chip just to replace the existing 80387 (if any). After upgraded, all the computation are done by RapidCAD-1 while RapidCAD-2 pretends to be a working co-processor so the system can take advantage of the co-processor functions (especially for 286/287 programs). Sometimes, we see RapidCAD-1 and RapidCAD-2 are being sold seperately, because many people do not understand how RapidCAD operates.
| Process: |
0.8 micron CHMOS IV, 800,000 transistors |
| Package: |
132-pin ceramic PGA |
| Data Bandwidth: |
32 bit |
| Working Voltage: |
5V |
| Released Clock Speed(s) |
25MHz - 33MHz |
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Intel RAPIDCAD [F]
Intel RAPIDCAD-1 [F] [B]
Intel RAPIDCAD-2 [F] [B]
Intel RapidCAD是英特爾有史以來第一款為舊款個人電腦所提供的升級套件（也就是OverDrive的始祖）。原386的使用者不需要更換主機板，只要把RapidCAD買回來將主機板上舊有的中央處理器晶片（CPU）替換掉，就可以享受接近486的運算能力。RapidCAD其實就是把486 DX晶片去掉內部快取記憶體然後裝入386的封裝裡面，RapidCAD也不支援486增加的新指令。不過由於386封裝的頻寬限制，RapidCAD對整體的效能提升比不上直接升級到486 DX。相同時脈下，486 DX可以有比386/387快上兩倍的速度，而RapidCAD在整數運算方面最多只能提升35%，在浮點運算方面，則可以提升將近70%。
Intel RapidCAD特殊的地方在於，它是由兩顆晶片組成，缺一不可。這歸咎於486 DX內建浮點運算器（FPU），而386則是將浮點運算器分開（就是387）。由於RapidCAD-1本身就含有浮點運算器（因為它就是486 DX閹割版），根本不需要387，所以RapidCAD-2就是用來替代原來主機板上的387晶片。RapidCAD-1負責所有的運算，而RapidCAD-2則是負責假裝浮點運算器，以防止舊有主機板以為沒有安裝浮點運算功能（尤其在執行286/287的程式時）。市面上有時候把RapidCAD-1與RapidCAD-2分開賣，這是就是不瞭解RapidCAD運作方式的結果。
| 製程： |
0.8 micron CHMOS IV, 800,000 transistors |
| 封裝： |
132-pin ceramic PGA |
| 資料頻寬： |
32 bit |
| 工作電壓： |
5V |
| 工作時脈： |
25MHz - 33MHz |
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Intel RAPIDCAD 正
Intel RAPIDCAD-1 正 反
Intel RAPIDCAD-2 正 反
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