This includes the keyboard, video display, printer and communications port.
Output is discarded and input returns zero.
This byte contains the low byte of the driver routine that services this device. This byte contains the high byte of the driver routine that services this device. These three bytes are for the driver routine to use as variable storage. It is up to the driver to define their use. The DCT contains the memory variables LDOS needs in order to determine the disk's geometry as well as the address of the driver routine that services requests to the drive.