Standard Disk Interconnect

The Standard Disk Interconnect (SDI, sometimes Standard Disk Interface) was used by Digital Equipment Corporation for its line of RAxx disks, for example the RA90. There were two bi-directional serial communications paths between the controller and the drive. One path was for messages (from the controller to the drive) and responses (from the drive to the controller); messages controlled seeking, setting drive parameters, reporting errors, etc. This path was also used to transmit data to and from the drive. The other path consisted of a continuously transmitted set of control (controller-to-drive) or status (drive-to-controller) bits. There were about 6 bits in each direction, and they served the same purpose as having six dedicated lines in each direction.

Standard Disk Interconnect

The Standard Disk Interconnect (SDI, sometimes Standard Disk Interface) was used by Digital Equipment Corporation for its line of RAxx disks, for example the RA90. There were two bi-directional serial communications paths between the controller and the drive. One path was for messages (from the controller to the drive) and responses (from the drive to the controller); messages controlled seeking, setting drive parameters, reporting errors, etc. This path was also used to transmit data to and from the drive. The other path consisted of a continuously transmitted set of control (controller-to-drive) or status (drive-to-controller) bits. There were about 6 bits in each direction, and they served the same purpose as having six dedicated lines in each direction.