You receive the following error message at startup after HIMEM.SYS version3.10 tests extended (XMS) memory:
ERROR: HIMEM.SYS has detected unreliable XMS memory at address XXXX:XXXXh. XMS driver not installed.
This error may be caused by a fault in the computer's external cachecontroller or by bad or mismatched memory chips on the external cache(generally 64, 128, or 256K cache SRAM). If disabling the external cachedoes not correct this problem, there may be a problem with the motherboardat the current processor speed, A20 handler problems, or bad or mismatchedmain system RAM chips.
Use the following troubleshooting procedures to isolate the cause of theXMS test failure:
Disable the external cache (also known as "secondary cache" or"CPU cache") in CMOS. For information about how to do so, referto the documentation included with your computer or contactyour hardware manufacturer.
NOTE: If disabling the external cache corrects the problem, replace the memory (SRAM) on the cache with the type and speed chips recommended byyour hardware manufacturer. If this does not correct the problem, youmay have a bad cache controller. Contact your hardware manufacturer formore information.
Disable Turbo in CMOS.
Disable Fast Gate A20 and Fast A20 Display in CMOS.
Try different machine switches with HIMEM.SYS (/M:2, 11, 12, and 13).For more information on this procedure, type "help HIMEM.SYS" (withoutthe quotation marks) at the MS-DOS command prompt.
Replace main system RAM chips with the type and speed memory modulesrecommended by your hardware manufacturer.
NOTE: You can disable XMS memory testing by adding /TESTMEM:OFF to the device line that loads HIMEM.SYS in your CONFIG.SYS file. For example,
Disabling XMS memory testing may allow HIMEM.SYS to load, but you mayexperience random file corruption, system instability, or other problemsuntil the underlying hardware problem is resolved.
The HIMEM.SYS version 3.10 included with MS-DOS 6.2 and Windows forWorkgroups 3.11 automatically performs an XMS memory check (/TESTMEM:ON)when loading. Note that the version of HIMEM.SYS included with Windows 95(3.95) does not automatically perform an XMS memory check unless the/TESTMEM:ON parameter is set in the Config.sys file.
The nature of the HIMEM.SYS test, as opposed to the ROM BIOS power-onmemory test, is that HIMEM.SYS writes series of 0FFh's and 000h's invarious 32-bit combinations. The ROM BIOS test does not generate difficultbus-loading conditions; instead, it checks for hard stuck bits (fatallybad memory cells). Therefore, HIMEM.SYS is much more likely to detectgeneral-purpose hardware problems. The ROM BIOS test generally detectsseriously flawed main-memory RAM chips themselves. (This is not to saythat main RAM can be ruled out when HIMEM.SYS detects a failure but ROMBIOS does not.)
Other symptoms of unreliable XMS memory may include file corruption orsystem hangs in applications that use XMS memory. For example, you mayexperience persistent corruption of group files (.GRP) in Windows or yoursystem may stop responding.
Windows 95 loads HIMEM.SYS by default, and no DEVICE= line isrequired in CONFIG.SYS. The default behavior for HIMEM.SYS duringa normal Windows 95 boot is to not test XMS memory. That is, assumingno DEVICE= line in CONFIG.SYS, Windows 95 will automatically loadHIMEM.SYS but it will not perform the XMS memory check discussed inthis article.
Windows 95 Safe mode tests XMS memory automatically (/TESTMEM:ON), oryou can manually add the following line to CONFIG.SYS to force theWindows 95 HIMEM.SYS to test XMS memory: