ACCESS.bus

ACCESS.bus, or A.b for short, is a peripheral-interconnect computer bus developed by Philips and DEC in the early 1990s, based on Philips' I²C system. It is similar in purpose to USB, in that it allows low-speed devices to be added or removed from a computer on the fly. While it was made available earlier than USB, it never became popular as USB gained in popularity.

Apple Computer's Apple Desktop Bus (ADB), introduced in the mid-1980s, allowed all sorts of low-speed devices like mice and keyboards to be daisy-chained into a single port on the computer, greatly reducing the number of ports needed, as well as the resulting cable clutter. ADB was universal on the Macintosh line by the late 1980s, and offered a clear advantage over the profusion of standards being used on PCs.

A.b was an attempt to reproduce these qualities in a new standard for the PC and workstation market. It had two additional advantages over ADB; hot plugging (plug-n-play) and the ability for the devices to have their own host controllers so devices could be plugged together without the need for a host computer to control the communications. Philips also suggested that the ability to plug any A.b device into any computer meant that people with special devices, like mice designed for people with disabilities, might carry their device from machine to machine.

An industry group, the ACCESS.bus Industry Group, or ABIG, was created in 1993 to control the development of the standard. There were 29 voting members of the group, including Microsoft. By this point DEC had introduced A.b on some of their workstations and a number of peripherals had been introduced by a variety of companies.

Development of USB began the next year, in 1994, and the consortium included a number of the members of the A.b group, notably DEC and Microsoft. Interest in A.b waned, leaving Philips as the primary supporter. A.b had a number of technical advantages over USB, which would not re-appear on that system until years later, and it was also easier and less expensive to implement. However, it was also much slower than USB, ten to a hundred times. USB fit neatly into the performance niche between A.b and Firewire, which made it practical to design a system with USB alone. Intel's backing was another deciding factor; the company began including USB controllers in the standard motherboard control chips, making the cost of implementation roughly that of the connector.

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