Apple Desktop Bus
 
The ADB Icon and an early ADB keyboard.
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| Type | Human input device interface | ||
|---|---|---|---|
| Designer | Steve Wozniak/Apple Computer | ||
| Designed | 1986 | ||
| Manufacturer | Apple Computer Inc. | ||
| Produced | 1986 to 1999 | ||
| Superseded | RS-422/6522 keyboard and mouse | ||
| Superseded by | USB and FireWire (1998-1999) | ||
| Hot pluggable | occasional support | ||
| External | yes | ||
| Pins | 4 | ||
| Connector | Mini-DIN | ||
| Data signal | Bi-directional serial command stream | ||
| Bitrate | 125 kbit/s maximum (~10 kbit/s actual) |
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| Max. devices | 16 maximum (~5 actual, 3 supported) |
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| Protocol | Serial | ||
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| Female socket from the front. | |||
| Pin 1 | ADB | Data | |
| Pin 2 | PSW | Power on | |
| Pin 3 | +5 V | +5 volts power | |
| Pin 4 | GND | Ground | |
| Same connector as S-Video | |||
Apple Desktop Bus (ADB) is a bit-serial peripheral bus connecting low-speed devices to computers. It was introduced on the Apple IIGS in 1986 as a way to support low-cost devices like keyboards and mice, allowing them to be connected together in a daisy chain without the need for hubs or other devices. ADB was quickly introduced on later Macintosh models, on later models of NeXT computers, and saw some other 3rd party use as well. Like the similar PS/2 connector used in many PC-compatibles at the time, ADB was rapidly replaced by USB as that system became popular in the late 1990s; the last external ADB port on an Apple product was in 1999, though it remained as an internal-only bus on some Mac models into the 2000s.
Early during the creation of the Macintosh computer, the engineering team had selected the fairly sophisticated Zilog 8530 to supply serial communications. This was initially done to allow multiple devices to be plugged into a single port, using simple implemented inside the 8530 to allow them to send and receive data with the host computer. The original design, known as AppleBus, had many of the same features as USB in terms of performance and device support.
During development of the AppleBus system, computer networking became a vitally important feature of any computer system. With no card slots, the Macintosh was unable to easily add support for Ethernet or similar local area networking standards. Work on AppleBus was re-directed to networking purposes, and was released in 1985 as the AppleTalk system. This left the Mac with the original single-purpose mouse and keyboard ports, and no general purpose system for low-speed devices to use.
ADB was created by Steve Wozniak, who had been looking for a project to work on in the mid-1980s. Someone suggested that he should create a new connection system for devices like mice and keyboards, one that would require only a single daisy-chained cable, and be inexpensive to implement. As the story goes, he went away for a month and came back with ADB.
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Wikipedia