The Powermate External Hard Disk drives were sold in 20 MB and 40 MB versions. They consisted of a small external enclosure housing the hard drive, an external power supply and a left or center slot interface board. In addition to the hard drive port, the center slot interface board provided a hard drive boot PROM socket, a printer port and a memory board bank-switching port. The left-slot board required a boot disk or tape or a center-slot board with a boot PROM on it to boot up the hard disk. 