Editing Conventional memory (section)

=== Upper memory blocks and loading high ===
As DOS applications grew larger and more complex in the late 1980s and early 1990s, it became common practice to free up conventional memory by moving the device drivers and TSR programs into upper memory blocks (UMBs) in the [[upper memory area]] (UMA) at boot, in order to maximize the conventional memory available for applications. This had the advantage of not requiring hardware changes, and preserved application compatibility.

This feature was first provided by third-party products such as [[QEMM]], before being built into [[DR&nbsp;DOS 5.0]] in 1990 then [[MS-DOS 5.0]] in 1991. Most users used the accompanying {{mono|[[EMM386]]}} driver provided in MS-DOS 5, but third-party products from companies such as [[QEMM]] also proved popular.

At startup, drivers could be loaded high using the "[[DEVICEHIGH (CONFIG.SYS directive)|DEVICEHIGH]]=" directive, while TSRs could be loaded high using the "[[LOADHIGH]]", "[[LH (DOS command)|LH]]" or "[[HILOAD]]" directives. If the operation failed, the driver or TSR would automatically load into the regular conventional memory instead.

[[CONFIG.SYS]], loading ANSI.SYS into UMBs, no EMS support enabled:
 DEVICE=C:\DOS\HIMEM.SYS
 DEVICE=C:\DOS\EMM386.EXE NOEMS
 DEVICEHIGH=C:\DOS\ANSI.SYS

[[AUTOEXEC.BAT]], loading MOUSE, DOSKEY, and SMARTDRV into UMBs if possible:
 LH C:\DOS\MOUSE.EXE
 LH C:\DOS\DOSKEY.EXE
 LH C:\DOS\SMARTDRV.EXE

The ability of DOS versions 5.0 and later to move their own system core code into the [[high memory area]] (HMA) through the [[DOS (CONFIG.SYS directive)|DOS]]=HIGH command gave another boost to free memory.