Q-Bus
| Q-Bus | |
DEC MicroVAX II CPU card (quad height) | |
| Created by | Digital Equipment Corporation |
|---|---|
| Supersedes | Unibus |
| Superseded by | VAXBI bus (1986) |
| Width in bits | 8 or 16-bit data, 16-bit address extended to 22-bit |
| No. of devices | 127 in theory, ~20 in practice |
| Style | Parallel |
| Hotplugging interface | No |
| External interface | No |
The Q-bus, also known as the LSI-11 Bus, is one of several bus technologies used with PDP and MicroVAX computer systems previously manufactured by the Digital Equipment Corporation of Maynard, Massachusetts.
The Q-bus is a less expensive version of Unibus using multiplexing so that address and data signals share the same wires. This allows both a physically smaller and less-expensive implementation of essentially the same functionality.
Over time, the physical address range of the Q-bus was expanded from 16 to 18 and then 22 bits. Block transfer modes were also added to the Q-bus.