DOCUMENT:Q116256 24-JUL-2001 [msdos] TITLE :Himem.sys Cannot Address More Than 64 MB of Memory PRODUCT :Microsoft Disk Operating System PROD/VER:MS-DOS:4.x,5.x,6.0,6.2,6.21,6.22; WINDOWS:3.1,3.11,95 OPER/SYS: KEYWORDS:kbhw kbtool win31 msdos win95 kbHardware ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft MS-DOS operating system versions 4.0, 4.01, 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22 - Microsoft Windows versions 3.1, 3.11 - Microsoft Windows 95 ------------------------------------------------------------------------------- SYMPTOMS ======== Himem.sys does not report or use more than 64 megabytes (MB) of installed memory on computers with an Industry Standard Architecture (ISA) or Micro Channel Architecture (MCA) bus. CAUSE ===== ISA Buses --------- ISA buses lack a standard BIOS interrupt routine for reporting more than 64 MB of memory. Himem.sys depends on the INT 15 function 88 service to determine installed memory, and this function is limited to 65,535 kilobytes (64 MB). MCA Buses --------- MCA-based computers add the INT 15 function C7 service to report installed memory. Although this function can report more than 64 MB of memory, Himem.sys has no code to support it. As a result, Himem.sys uses the standard INT 15 function 88 call, which is limited to 64 MB of memory. MORE INFORMATION ================ This limitation does not apply to computers with an Extended Industry Standard Architecture (EISA) bus. On EISA-based computers, Himem.sys scans each slot for device information, which means that it can report up to 4 gigabytes (GB). NOTE: You may need to use the /EISA switch on the Himem.sys line in your Config.sys file. Note that although Himem.sys addresses only the first 64 MB of memory, the Windows 95 virtual memory manager (Vmm32.vxd) takes over memory management tasks from Himem.sys. Vmm32.vxd can address more than 64 MB of memory. Additional query words: 4.x 5.x 6.00 6.20 6.21 6.22 3.10 3.11 busses mem xms ram ====================================================================== Keywords : kbhw kbtool win31 msdos win95 kbHardware Technology : kbWin3xSearch kbWin95search kbZNotKeyword3 kbWin310 kbWin311 kbMSDOSSearch kbMSDOS400 kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS500 kbMSDOS401 kbMSDOS500a Version : MS-DOS:4.x,5.x,6.0,6.2,6.21,6.22; WINDOWS:3.1,3.11,95 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.