INT 27 - DOS 1+ - TERMINATE AND STAY RESIDENT
DX = number of bytes to keep resident (max FFF0h)
CS = segment of PSP
Return: never
Notes:  this is an obsolete call
INT 22, INT 23, and INT 24 are restored from the PSP
does not close any open files
the minimum number of bytes which will remain resident is 110h for
DOS 2.x and 60h for DOS 3+; there is no minimum for DOS 1.x, which
implements this service in COMMAND.COM rather than the DOS kernel

See also: 2131

27 - DOS 1+ - TERMINATE AND STAY RESIDENT