Article ID: 109845 - View products that this article applies to.
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You receive the following error message at startup after HIMEM.SYS version 3.10 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 cache controller or by bad or mismatched memory chips on the external cache (generally 64, 128, or 256K cache SRAM). If disabling the external cache does not correct this problem, there may be a problem with the motherboard at the current processor speed, A20 handler problems, or bad or mismatched main system RAM chips.
Use the following troubleshooting procedures to isolate the cause of the XMS test failure:
The HIMEM.SYS version 3.10 included with MS-DOS 6.2 and Windows for Workgroups 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-on memory test, is that HIMEM.SYS writes series of 0FFh's and 000h's in various 32-bit combinations. The ROM BIOS test does not generate difficult bus-loading conditions; instead, it checks for hard stuck bits (fatally bad memory cells). Therefore, HIMEM.SYS is much more likely to detect general-purpose hardware problems. The ROM BIOS test generally detects seriously flawed main-memory RAM chips themselves. (This is not to say that main RAM can be ruled out when HIMEM.SYS detects a failure but ROM BIOS does not.)
Other symptoms of unreliable XMS memory may include file corruption or system hangs in applications that use XMS memory. For example, you may experience persistent corruption of group files (.GRP) in Windows or your system may stop responding.
Windows 95 loads HIMEM.SYS by default, and no DEVICE= line is required in CONFIG.SYS. The default behavior for HIMEM.SYS during a normal Windows 95 boot is to not test XMS memory. That is, assuming no DEVICE= line in CONFIG.SYS, Windows 95 will automatically load HIMEM.SYS but it will not perform the XMS memory check discussed in this article.
Windows 95 Safe mode tests XMS memory automatically (/TESTMEM:ON), or you can manually add the following line to CONFIG.SYS to force the Windows 95 HIMEM.SYS to test XMS memory:
Article ID: 109845 - Last Review: January 18, 2007 - Revision: 2.1
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