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Joystick Magazine 1997 February
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cd no21 joystick no79.iso
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pc
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data
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patches
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patch
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cyrix
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nt406x86.txt
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1996-11-27
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4KB
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64 lines
THE PROBLEM:
On IBM/Cyrix 6x86 rev2.6 and prior CPU's, Windows NT 4.0 causes Write-Through cache
mode to be enabled instead of Write-Back cache mode, which slows down system
performance by about 20%. Apparently, on Microsoft's hardware compatibility testing
(HCT) for Windows NT 4.0, they saw a problem with rev2.6 and prior 6x86 CPU's and wrote
code to force Write-Through cache mode on for stability. It seems that Microsoft did not see
any problems with rev 2.7 or beyond 6x86 CPU's in their HCT... Check IBM's server for
more on this problem.
At this point in time, there are NO KNOWN actual applications that have caused a rev2.6 or
prior 6x86 CPU to fail or hang using Write-Back cache mode with programs under Windows
NT 4.0. So for real-world applications there does not appear to be any issue.
A POSSIBLE SOLUTION:
Place your Windows NT 4.O operating system (O/S) so that it is in Administrator mode.
Download PUZZLE.EXE from here or http://www.chips.ibm.com/products/x86/doclist.html
and put it on your C: drive. This is a 6x86 system benchmark program. Run PUZZLE.EXE in
a DOS window and record your score. With a 133MHz 6x86 (P166+) rev2.6 or prior CPU,
you should get a score of 1.3 - 1.5 when running with Windows NT 4.0.
Download nt406x86.zip and unzip this file. It will decompress into 4 files which you should
copy to your floppy A: drive. The files are: DRVON.BAT, IBM_WB.SYS, INSTDRV.EXE,
and NTDRV.EXE.
If Windows NT 4.0 is installed on your C: drive, then proceed to the next bullet. However, if
NT 4.0 is installed to a drive other than C: you will need to modify the DRVON.BAT file.
Using a text editor, open the DRVON.BAT file. It should have the following lines:
cd\ntdrv
instdrv simpldrv c:\ntdrv\ibm_wb.sys
Change the C: to whatever drive that Windows NT 4.0 is installed on, like D:, E:, etc.
From a DOS window, type "A:NTDRV" (or "B:NTDRV if B: is your floppy drive) and enter
"1." This installs a driver that will enable Write-Back cache mode upon system boot-up.
NTDRV will ask for the drive that NT 4.0 is installed on which should be the same drive
listed in the DRVON.BAT file as discussed above. To uninstall the driver, re-run
"A:NTDRV" and enter "2" and the system will be back at it's default Write-Through cache
mode.
Once the driver has been installed, reboot your system and run the PUZZLE.EXE program
again from a DOS window. For a 6x86 133MHz (P166+) you should now get a score of 0.8 or
0.9 and your system will run Windows NT 4.0 at the same performance as a rev2.7 or later
6x86 CPU, and definitely faster than a comparable Pentium !!
WHAT DOES THE PATCH DO ?
The patch makes a folder in the NT start-up where it puts a driver that sets Bit 29 (NW or
Not-Write Back) in the CR0 to 0 so the processor operates in Write-Back cache mode.
DISCLAIMER:
I do not myself run Windows NT 4.0 so I have no hands-on experience with that O/S or this
fix. However, I have talked to people who have used this procedure with Windows NT 4.0
and a rev 2.6 or prior 6x86 CPU and they have not seen any problems. Feel free to try this
out at your own risk. Also note that this "patch" is NOT ENDORSED by IBM, Cyrix,
or any other company. It is intended as a possible solution to the Rev 2.6 and
prior 6x86 Windows NT 4.0 performance problem. By enabling Write-Back Cache mode
on these Rev 6x86 chips, instability MAY be introduced into the Windows NT 4.0
operating system.