Troubleshooting HIMEM.SYS 3.10 XMS Test (TESTMEM) Failures (109845)

The information in this article applies to:
    Microsoft Windows 98
    Microsoft Windows 95
    Microsoft MS-DOS operating system 6.2
    Microsoft MS-DOS operating system 6.21
    Microsoft MS-DOS operating system 6.22
    Microsoft Windows for Workgroups 3.11

This article was previously published under Q109845
If this article does not describe your hardware-related issue, please see the following Microsoft Web site to view more articles about hardware:


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:
    Disable the external cache (also known as "secondary cache" or "CPU cache") in CMOS. For information about how to do so, refer to the documentation included with your computer or contact your 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 by your hardware manufacturer. If this does not correct the problem, you may have a bad cache controller. Contact your hardware manufacturer for more 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" (without the quotation marks) at the MS-DOS command prompt.
    Replace main system RAM chips with the type and speed memory modules recommended 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 may experience random file corruption, system instability, or other problems until the underlying hardware problem is resolved.


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:

Modification Type: Major Last Reviewed: 12/28/2001
Keywords: kbprb KB109845