Two of the most important uses of the DEVICE command involve HIMEM.SYS and DOS itself.
Since our PCs cannot address extended memory without HIMEM.SYS, it makes sense that HIMEM.SYS would have to be loaded before we could load drivers into upper memory or into a special area of memory called the High Memory Area.
Included with the DOS 5.0 upgrade is HIMEM.SYS, a program that provides access to extended memory and insures that no two programs can use the same memory address.
Using HIMEM.SYS and EMM386.SYS and loading MS-DOS into upper memory yielded 613 KB of usable conventional memory and 5,460 KB of extended or expanded memory as needed.
For example, HIMEM.SYS, Microsoft's extended memory manager, cannot be loaded using DEVICEHIGH or LOADHIGH because, until it is loaded, DOS does not even know extended memory exists.
The HIMEM.SYS and EMM386.EXE programs discussed earlier are the first essential step in activating extended and upper memory.
: The MS-DOS extended-memory manager, HIMEM, automatically tests your system's memory when you start your computer.
The install program will detect DOS 5.0 or Windows HIMEM.SYS
and ask if you want HIMEM.SYS
Most Windows users are at least somewhat familiar with HIMEM.SYS because it is an extended memory manager and most computers running Windows have some extended memory.
HIMEM.SYS is of course fully compatible with the Extended Memory Specification, or XMS, not to be confused with EMS, the Expanded Memory Specification.
DOS memory management includes two components, HIMEM.SYS
and EMM386.EXE, that permit the use of available memory between 640K and 1MB, as well as simulated expanded memory.
Typically, an extended memory device driver such as HIMEM.SYS
will do the trick.