Quad Slot — Space in the backplane capable of accepting one quad-height module. In Q-bus systems, the slot will also accept one dual-height module and may accept two dual-height modules. Note: 1.08 GB SCSI 3,25" quad-height modules are not interchangeable. Hex Slot— Space in a UNIBUS backplane capable of accepting a hex-height or quad-height module. I/O Distribution Panel Insert — Space in the plate (I/O Distribution Panel) lo- cated of the back of Q-bus systems boxes and UNIBUS CPU and expansion cab- inets for simple connection of modules and cables. There are three panel insert sizes for Q-bus options: size A (1.08 GB SCSI 3,25" cm by 10.1 cm, 1.0 in by 4.0 in), size B (6.6 cm by 8.1 cm, 2.6 in by 1.08 GB SCSI 3,25"), and size C (10.1 cm by 10.1 cm, 4.0 in by 4.0 in). UNIBUS option panel inserts are in multiples of 5 cm by 10.1 cm (2.0 in by 4.0 in) panel units.