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Disable 387 FPU
- Thread starter Xacalite
- Start date
kgober
Veteran Member
As far as I know there's no way to disable the hardware via a software setting.
But many math libraries had a configuration option to disable their use of floating-point hardware (presumably to allow easy testing without physically removing the chip), for example by setting the "NO87=1" environment variable. Do you have documentation for this math software? It might have such an option.
But many math libraries had a configuration option to disable their use of floating-point hardware (presumably to allow easy testing without physically removing the chip), for example by setting the "NO87=1" environment variable. Do you have documentation for this math software? It might have such an option.
So I'm benchmarking some math software on a 386 with FPU, and want to measure the performance impact of the FPU.
But I don't feel like physically removing the chip - anybody knows a program to disable it?
I have a 386 with an AMIBIOS. Under 'Advanced CMOS Setup' it has a provision for 'Numerical Processor Test', but no way to enable or disable the FPU.
twistedpneumatic
Experienced Member
Write software that ises the CPU and FPU directly? Find some different software?
Stone
10k Member
Sorry, but that's way beyond my pay grade.Write software that ises the CPU and FPU directly? Find some different software?
twistedpneumatic
Experienced Member
How about shifting that i key one to the left. Uses sounds a little better.
Too bad...
I tried to prevent software from using FPU by zeroing the bit 1 at 0040h:0010h, but it's not enough...
Checkit still detects FPU and benchmarks it as usual.
Mathematica on startup displays a warning about the lack of FPU, but later on works as usual.
I tried to prevent software from using FPU by zeroing the bit 1 at 0040h:0010h, but it's not enough...
Checkit still detects FPU and benchmarks it as usual.
Mathematica on startup displays a warning about the lack of FPU, but later on works as usual.
Stone
10k Member
Since you're the OP I would suspect that's your responsibility.How about shifting that i key one to the left.
Stone
10k Member
Have you tried a coprocessor emulator?Mathematica on startup displays a warning about the lack of FPU, but later on works as usual.
No, but I doubt it would do any change.Have you tried a coprocessor emulator?
Coprocessor emulators are based on some exception generated by CPU on FPU instructions executed without an actual FPU, right?
If the FPU is present, such exceptions should never occur.
I remember there was a DOS utility, hide87.com, for that purpose.So I'm benchmarking some math software on a 386 with FPU, and want to measure the performance impact of the FPU.
But I don't feel like physically removing the chip - anybody knows a program to disable it?
I believe it was from German c`t magazine. However, I have not really tested it.
There was some problem with the forum, recent posts got lost, so let me reply again...I remember there was a DOS utility, hide87.com, for that purpose.
I believe it was from German c`t magazine. However, I have not really tested it.
I tried HIDE87.COM:
"Terminate and Stay Resident code that hooks Int 11h (BIOS equipment check) to fool some programs (notably Windows' Kernel) into thinking there isn't a math coprocessor."
But it's of limited use - eg. Checkit 3.0 still detects FPU and benchmarks it as usual.
Thanks for the feedback, Xacalite!
I almost thought my reply was lost.
Also sorry for the program. I wasn't sure how well it works.
Maybe there are different versions of the program..
The version comes with Winfloat outputs a different string than the c't version I'm familiar with (see attachment).
I almost thought my reply was lost.
Also sorry for the program. I wasn't sure how well it works.
Maybe there are different versions of the program..
The version comes with Winfloat outputs a different string than the c't version I'm familiar with (see attachment).