Microsoft KB Archive/39547

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Older Versions of VDISK.SYS Will Not Work with HIMEM.SYS PSS ID Number: Q39547 Article last modified on 01-05-1989

2.04 2.05



The Microsoft XMS (eXtended Memory Specification) driver HIMEM.SYS does not work correctly with older releases of the IBM PC-DOS virtual disk driver VDISK.SYS. Older releases of this driver use an extended-memory allocation scheme that is incompatible with HIMEM.SYS. However, the version of VDISK.SYS included with IBM PC-DOS Version 4.00 WILL work with HIMEM.SYS because IBM has changed the extended-memory allocation scheme that the VDISK.SYS driver uses so that it is now compatible with HIMEM.SYS. The XMS document “eXtended Memory Specification” Version 2.00 mentions that HIMEM.SYS will not work with VDISK allocation schemes. However, it does not mention these changes in IBM PC-DOS Version 4.00’s VDISK.SYS.

HIMEM.SYS will work with the Microsoft virtual disk driver, RAMDRIVE.SYS, included with Microsoft Windows and Microsoft MS-DOS. In most cases, OEM releases of RAMDRIVE.SYS and VDISK.SYS behave exactly like the standard Microsoft and IBM releases of these respective drivers, at least in terms of extended-memory allocation.


Copyright Microsoft Corporation 1989.