In MS-DOS systems, the 640K of memory located at linear addresses 00000000-0009FFFF. The lower part of this region (00000000-000005FF) is generally reserved for the interrupt vector table and the BIOS and MS-DOS data areas, while the remainder, minus any memory taken up by TSR programs and device driver modules, is available as the Transient Program Area.

Conventional memory is a very important system resource in MS-DOS systems.
