Abstract: A modular disk memory apparatus provides a modularly expandable, multi-gigabyte auxiliary memory for a computer or other host electronic device, and includes multiple, parallel serial data channels to maximize bidirectional data transfer rates between the apparatus and the host device. Maximization of READ/WRITE data transfer rates within the apparatus is achieved by utilizing a large number of small hard disk drives, typically eight 2.5-inch drives on each of a plurality of Disk Storage Modules, each including a plug-in printed circuit board capable of holding two 5-1/4 inch drives, thereby increasing the maximum data transfer rate per unit volume of the modules by a factor of two.