Abstract: A CD-ROM drive unit includes a disk transport tray moved between an open position, in which a compact disk, exposed outside the drive unit, can be removed and replaced, and a closed position, in which data can be read. The drive unit also includes a disk reading mechanism, which rotates the disk, and which moves an optical sensor along the disk as required for reading information from the disk. Motions obtained from this disk reading mechanism are used to drive the disk transport tray between the positions. In a first version of the device, a spindle motor drives a spindle, on which a disk is placed, in a forward direction to effect reading data and in a reverse direction to effect movement of the disk transport tray. A one-way clutch is used to discriminate between driver directions, only operating a mechanism to move the tray when the spindle motor is driving in reverse.

Abstract: A microcomputer system has a first, low order address, memory soldered to the planar printed circuit board and can accept further memory pluggable into a socket on the board. At power on self test, the memories are tested, and, if an error is detected in the first memory, this memory is disabled by directing the lowest order memory addresses to the second memory and reducing the highest order addresses by the number of locations in the first memory.