HP 7920 Disc Drive

The 7920 represented the beginning of the next generation of system hard disc drives up from the 790X drives. The 7920 drives held removable 50MB disc platters. The 7920M also included a controller into which an additional seven slave drives could be connected (7920S). The 7925 disc drives (introduced in 1978) came with 120MB removable disc platters. These drives had an average seek time of 25ms and a data transfer rate of 938K per second.