INT 21,36 - Get Disk Free Space

AH = 36h

DL = drive number (0=default, 1=A:)

on return:

AX = sectors per cluster

= FFFF if drive is invalid

BX = number of available clusters

CX = number of bytes per sector

DX = number of clusters per drive

- used to determine available space on specified disk

- see ~INT 21,1B~ ~INT 21,1C~