ddev@wam.umd.edu (Don DeVoe) (02/14/90)
Can anyone tell me if the 68882 and '881 are pin compatible? I recently
obtained an '882, and I hope to replace my mac II's '881 with it. What I
need to know is A) will this switch work? B) Will I see any real performance
improvement? I kinda-sorta recall hearing that the '882 will work in a
mac II, but I don't really feel like risking my motherboard on it.
If anyone out there has successfuly swaped these chips in a macII, please
let me know!knapp@cs.utexas.edu (Edgar Knapp) (02/15/90)
In article <1990Feb14.050221.16897@wam.umd.edu> ddev@wam.umd.edu (Don DeVoe) writes: > > Can anyone tell me if the 68882 and '881 are pin compatible? I recently >obtained an '882, and I hope to replace my mac II's '881 with it. What I >need to know is A) will this switch work? B) Will I see any real performance >improvement? I kinda-sorta recall hearing that the '882 will work in a >mac II, but I don't really feel like risking my motherboard on it. [..] I have been running a 20 MHz 68882 for two months. It works without a hitch, and you do notice a performance gain, especially in programs like Mathematica that use the floating point chip heavily. By the way, I have both a 20 MHz and a 25 MHz MC68882 for sale ($150.- and $200.- respectively). Also, if someone wants my old 16 MHz MC68881 to use in an accelerator board it can be had for $50.-. Edgar (knapp@cs.utexas.edu)
rcfische@polyslo.CalPoly.EDU (Raymond C. Fischer) (02/15/90)
In article <1990Feb14.050221.16897@wam.umd.edu> ddev@wam.umd.edu (Don DeVoe) writes: > Can anyone tell me if the 68882 and '881 are pin compatible? I recently >obtained an '882, and I hope to replace my mac II's '881 with it. What I >need to know is A) will this switch work? B) Will I see any real performance >improvement? I kinda-sorta recall hearing that the '882 will work in a >mac II, but I don't really feel like risking my motherboard on it. The 68881 IS pin compatible with the 68882. Although I haven't tried it, I referred to the "MC68881/882 Floating-Point Coprocessor User's Manual" to make sure. Will you see any performance inprovement? Yes. How much? It depends. The '882 is faster, but it's speedup comes from increased efficiency rather than a complete redesign. The '882 improves the coprocessor interface to increase throughput and allows multiple '882 instructions to execute concurrently. With code optimized for the '882, the speedup can be 50%. No compilers that I know of do this optimization however, so your actual speedup will probably be more along the lines of 10%. Ray Fischer rcfische@polyslo.calpoly.edu > > If anyone out there has successfuly swaped these chips in a macII, please >let me know!