1 MB COMPAQ and AT&T Machines Can't Run HIMEM.SYS (81710)

SUMMARY

COMPAQ 286, 386, and 486 machines and the AT&T 6300 Plus, 6386 WGS, 6386/20 WGS implement a memory mapping scheme that does not allow for the installation of HIMEM.SYS if the machine has only 384K of extended memory.

This information applies to all versions of HIMEM.SYS.

COMPAQ and AT&T computers with more than 1 MB of memory installed function properly with HIMEM.SYS.

MORE INFORMATION

A COMPAQ 286, 386, or 486 with 1 megabyte (MB) installed has 640K base memory and remaps the 384K extended memory to the 0FA0000 address mark (to the 16 MB mark, not the 1 MB mark). Because the 384K of extended memory is not addressed contiguously above the 1 MB line, there is no extended memory in HMA (1024K-1088K). Therefore, MS-DOS has no place to load high. The AT&T/Olivetti computer functions in a similar manner.

This behavior occurs by design with COMPAQ and AT&T systems. The design decision was made by these manufacturers long before HIMEM.SYS was created. HIMEM.SYS relies on the capability of the 80286/80386/80486 processor to address 64K of extended memory at the 1024K line.

Loading HIMEM.SYS may appear to be successful on some machines while failing to load or causing system hangs on others. The success depends on the particular model of COMPAQ or AT&T in use. Alternative machine switches on HIMEM.SYS will not solve the problem.

COMPAQ has its own OEM version of HIMEM.SYS extended memory manager called HIMEM.EXE, which is included on the utilities disks with the COMPAQ Deskpro 80286, 80386, and 80486 based systems. It allows those systems with extended memory to access this extended memory using the extend memory specification (XMS). It also allows MS-DOS programs to use the 64K region of memory located just above the 1 MB address.

The version of HIMEM.EXE dated 6-14-90 works with Microsoft Windows version 3.0 and is recommended by COMPAQ for use on COMPAQ machines with less than 16 MB of memory.

For additional information, contact COMPAQ technical support or AT&T.

The products included here are manufactured by vendors independent of Microsoft; we make no warranty, implied or otherwise, regard these products' performance and reliability.