Int 21H, AH=44H, AL=09H

3.1 and higher

CHECK IF BLOCK DEVICE REMOTE

AX = 4409h
BL = drive number (00h = default, 01h = A:, etc)

CF clear if successful

    DX = device attribute word
	bit 15: drive is SUBSTituted
	bit 13: (DR DOS 3.41/5.0 local drives only) always set
		media ID needed
	bit 12: drive is remote
	bit  9: direct I/O not allowed
CF set on error
    AX = error code (01h,0Fh,15h) (see #01680 at AH=59h/BX=0000h)

on local drives, DX bits not listed above are the attribute word from the device driver header (see #01646 at AH=52h); for remote drives, the other bits appear to be undefined for MS-DOS versions prior to 5.0 (they are all cleared in DOS 5+)

checking whether DX=0800h on return appears to be a fairly reliable method for detecting Microsoft's RAMDRIVE, though not for other ramdisks (there appears to be no simple yet foolproof method for detecting ramdisks, although the presence of only a single copy of the FAT and only a single head on non-removable devices is a fairly good indicator); for Windows95, RAMDRIVE returns DX=4800h

for non-existent remote drives, this function sometimes returns AX=0015h (drive not ready) instead of AX=000Fh (invalid drive) on the first call; a subsequent call will return the correct error code

this function was not supported by Digital Research's DOS Plus

AX=4400h,AX=4408h,AX=440Ah,INT 2F/AX=122Bh

Text based on Ralf Brown Interrupt List Release 61