Can't see >16 MB under Windows 95? HIMEMUPD.EXE is the cure!

On an IBM PS/2 Model 77, 90 or 95 with more than 16 MB of memory (RAM) installed, Windows 95 only recognizes and uses 16 MB of memory. This is because HIMEM.SYS, the extended memory manager, only detects 16 MB of memory installed.


These computers use a nonstandard API for reporting memory in excess of 16 MB that is not supported by Windows 95.


This issue is resolved by the following updated file(s) for Windows 95 and OSR2, and later versions of these file(s):

HIMEM.SYS  ver 3.95 dated 10/2/95  33,127 bytes.

This and later versions of HIMEM.SYS support the API used by the computers listed in this article for reporting memory in excess of 16 MB.


Microsoft has confirmed this to be a problem in Microsoft Windows 95. An update to address this problem is now available, but is not fully regression tested and should be applied only to computers experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft does not recommend implementing this update at this time. Contact Microsoft Technical Support for additional information about the availability of this update.

This issue is resolved in Microsoft Windows 98.

More Information

The computers listed in this article use INT 15 AX=C700h to report memory above 16 MB. (Other IBM PS/2 Micro Channel computers may use INT 15 AX=E881h.) The updated version of HIMEM.SYS accepts a /P switch that causes HIMEM to use this API to detect memory in excess of 16 MB. Without the /P switch, the updated HIMEM does not use this API, and functions the same as the shipping version of HIMEM.

The new version of HIMEM.SYS reports itself as version 3.95, the same as the shipping version. Knowledge Base Reference Article: Q137755: No More Than 16 MB of Memory Reported on IBM PS/2 Model 77, 90.

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