Conventional Memory
This is the "standard" or "normal" computer
memory that exists on all PC-compatibles.

PCs support a maximum of 640K of conventional
memory.  TSRs, device drivers, and DOS itself
occupy some portion of that 640K.

Other types of memory require additional
support hardware (see EMS) or a 286-based or
better CPU (see XMS and HMA), or a 386-based
or better CPU (see UMB).
  DOS fns 48H, 49H, and 4aH work with
conventional memory by default.