SU (System Units) — Definition of space available in UNIBUS CPU and expan- sion cabinets for mounting backplane(s) to accommodate modules. For exam- ple, a 2,1 GB SCSI 3,25" box has five SUs worth of space that could accommodate up - to two DD11 DK backplanes and one DD11 CK backplane. - - Backplane — Hardware interface containing edge connector slots for insertion of modules. These backplanes allow for the connection of the modules to the bus and to a power supply source. For example, 2,1 GB SCSI 3,25". - - Dual-height Module — A 13.2-cm by 20.3-cm (5.22-in by 8-in) module with two connectors. Quad-height Module — A 26.5 cm by 20.3-cm (10.44-in by 8-in) module with - four connectors. Hex-height Module — A 39.6-cm by 20.3 cm (15.6 in by 8 in) module with six - - - connectors. Used only in 2,1 GB SCSI 3,25" systems. Dual Slot — Space in the backplane capable of accepting one dual-height module.