Int 21H, AH=44H, AL=06H

2 and higher

GET INPUT STATUS

AX = 4406h
BX = file handle

CF clear if successful

    AL = input status
	00h not ready (device) or at EOF (file)
	FFh ready
    AH may be destroyed (refer to note)
CF set on error
    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)

files may not register as being at EOF if positioned there by AH=42h
under DOS 5.0, on a successful return, AH contains either the next
  character which will be read or 1Ah if at EOF; under a Windows95
  DOS box, AH seems to be either unchanged or 00h
this function was not supported by Digital Research's DOS Plus
 the CLOCK$ device under DR DOS 3.41 always indicates 'Ready'; this was
  corrected in v5.0

AX=4407h,INT 2F/AX=122Bh

Text based on Ralf Brown Interrupt List Release 61