Himem.sys Cannot Address More Than 64 MB of Memory (116256)
The information in this article applies to:
• Microsoft MS-DOS operating system 4.0
• Microsoft MS-DOS operating system 4.01
• Microsoft MS-DOS operating system 5.0
• Microsoft MS-DOS operating system 5.0a
• Microsoft MS-DOS operating system 6.0
• Microsoft MS-DOS operating system 6.2
• Microsoft MS-DOS operating system 6.21
• Microsoft MS-DOS operating system 6.22
• Microsoft Windows 3.1
• Microsoft Windows 3.11
• Microsoft Windows 95
This article was previously published under Q116256
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.
| Modification Type: |
Major |
Last Reviewed: |
5/6/2003 |
| Keywords: |
kbHardware KB116256 |
|