Apple Desktop Bus

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ADB plug

Apple Desktop Bus, or ADB, is a serial interface developed by Apple for connecting peripherals such as keyboards, mice and graphics tablets to computers. ADB uses a mini-DIN 4 connector, identical to that used by S-video.

ADB was developed by Steve Wozniak for the Apple IIgs, and it was later introduced to the Macintosh II to replace the original Mac's keyboard-specific connector. ADB allows up to 16 devices to be "daisy-chained"—connected in series—to the host computer. ADB on the Macintosh was a hot-swap interface: Mac OS would scan the bus periodically during vertical blank interrupts for new devices. Nevertheless, Apple failed to provide surge protection on the bus, and hot-swapping ADB devices carried the risk of damaging the motherboard; as such, hot-swapping is widely proscribed.

Macintosh computers typically only provided one ADB port. The keyboard would connect to the computer, and the keyboard provided a downstream port for the mouse, which typically had a short cable. Early Macintosh ADB keyboards featured two bidirectional female ports, one on either side, and a detachable keyboard cable: the cable could be connected either port, and the port on the opposite side would be used for the mouse.

Apple discontinued the use of ADB with the transition to USB, starting with the first Apple iMac. The last computer with an ADB port was the blue-and-white 1999 Power Macintosh G3, which also had USB ports.


ADB peripheral to USB host


Honourable mentions

  • The ADB bUSBoy would have connected two USB peripherals to a ADB port. It never went into production because the USB Wombat had been introduced at a lower price.


See also

Category:Apple keyboards