Enable Extended Memory in MS-DOS 6.22

This article explains how to configure MS-DOS 6.22 to access Extended Memory (XMS) through the CONFIG.SYS configuration file. By loading the native Extended Memory Manager driver, users can surpass the standard 640 KB conventional memory barrier and make up to several gigabytes of RAM available for compatible DOS programs, utilities, and the operating system itself.

The Driver Line

To enable Extended Memory in MS-DOS 6.22, you must add the HIMEM.SYS device driver to your CONFIG.SYS file. The standard line is:

DEVICE=C:\DOS\HIMEM.SYS

If your MS-DOS system files are located in a different directory or on another drive, replace C:\DOS\ with the correct path to the HIMEM.SYS file.

How It Works

HIMEM.SYS is the Extended Memory Specification (XMS) manager provided with MS-DOS. Standard DOS can natively address only the first 1 MB of memory (the first 640 KB for conventional memory, and the remaining 384 KB for the Upper Memory Area). HIMEM.SYS manages the memory above the 1 MB address space, known as Extended Memory (XMS), and also controls the High Memory Area (HMA), which consists of the first 64 KB of extended memory.

Proper Placement in CONFIG.SYS

The HIMEM.SYS driver must be declared before any other memory managers or drivers that rely on extended memory.

A standard configuration in CONFIG.SYS typically looks like this:

DEVICE=C:\DOS\HIMEM.SYS
DOS=HIGH
  • DEVICE=C:\DOS\HIMEM.SYS: Initializes and enables access to Extended Memory.
  • DOS=HIGH: Instructs MS-DOS to load parts of its own kernel into the High Memory Area (HMA) provided by HIMEM.SYS, freeing up valuable conventional memory for applications.

If you also plan to use Expanded Memory (EMS) or Upper Memory Blocks (UMBs) via EMM386.EXE, the HIMEM.SYS line must always appear first:

DEVICE=C:\DOS\HIMEM.SYS
DEVICE=C:\DOS\EMM386.EXE NOEMS
DOS=HIGH,UMB

Verifying Extended Memory

After editing CONFIG.SYS, save the file and reboot the computer. To verify that Extended Memory is functioning properly, type the following command at the DOS prompt:

MEM

The output will display a memory summary table confirming that Extended Memory (XMS) is present, configured, and managed.