A brief history of Mac ports – low speed
Like most computers, Apple’s Macs have had five main types of port to allow them to be connected to external devices: low speed intended commonly for keyboards and other input devices, high speed often for connection to external storage, display, network, and audio. This brief history concentrates on the first of those.
The original 128K Macintosh launched in 1984 came with a good range of ports, including two RS-422 serial ports and a DB-19 supporting external floppy disk drives. It had separate mouse and keyboard ports, DE-8 and RJ-11 respectively. In 1986, Apple’s IIGS brought the first implementation of a new type of port, Apple Desktop Bus or ADB, that was introduced to the Mac SE and II the following year, replacing the original mouse and keyboard ports.
At the time, ADB was unique to Apple’s computers, although it was later adopted by NeXT. This uses a 4-pin mini-DIN connector to hook up a daisy-chain of peripherals. The theoretical maximum speed of ADB is 125 Kb/s, although around 62 Kb/s was closer to that experienced in practice. Among these ADB devices came dongles, used to enforce software copy-protection. Devices on an ADB chain each have an address, defaulting to $2 for keyboards, and $3 for mice.
