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A Nubus is a 32-bit parallel computer bus. It was created by the Massachusetts Institute of Technology and originated from the NuMachine workstation project, which designed workstations to interface with LANs using microprocessors. The MIT laboratory team for the NuMachine worked in collaboration with Western Digital.
The original Nubus and NuMachine were designed for the Western Union NuMachine and for the Lisp Machines Incorporated LMI-Lambda. The NuMachine was used in components by Texas Instruments, Next, Incorporated (NeXT) and Apple Computer. In 1983 the NuMachine was bought by Texas Instruments. It was replaced by the TI Explorer in 1985.
At the time, Nubus was considered a significant advancement, since most computer interfaces used an 8-bit bus. Today, Nubus is no longer used and was replaced mostly by the peripheral component interconnect (PCI) and other parallel buses.
The Nubus card uses pins instead of an edge connector, which is used on a PCI or industry standard architecture card.
Not only did the Nubus introduce a 32-bit bus, but it had an ID structure permitting cards to be identified by the host during booting. At the time, the majority of buses used pins on the CPU, which connected to the backplane. This structure corresponded to data standards and signaling, which included configuring the memory and the card, interrupts and other time consuming tasks. In fact, Nubus was one of the first plug-and-play designs.
However, the Nubus architecture required a controller chip between the I/O chips on the card and the bus. This scheme required additional cost and complexity compared to the simple bus systems supported by minimal I/O chips.
Nubus cards can be designed as either a master or slave. A master manages bus requests for bus mastery and can secure the bus from access by other Nubus devices for an allotted time. The slave responds to requests, transmits non-master requests and does not need support for the entire 32-bit transfer.
A 24-bit Nubus card is utilized on the Macintosh II series. It is called a 24-bit aliasing and supports address lines 0 to 23. Nubus was also chosen for NeXT Computer modules, but it had a different printed circuit board design.