NuBus

NuBus was originally developed at MIT and was used by Apple Computer and NeXT based computers until the mid-1990s.

Essentially replaced by PCI.

NuBus ’90 Features

The NuBus, the industry-standard expansion bus used in all Macintosh II–family computers, runs at a clock rate of 10 MHz. The NuBus in the Macintosh Centris 650 and Macintosh Quadra 800 computers includes several features of NuBus ’90, including a clock signal at 20 MHz, twice the normal rate. The NuBus adapter for the Macintosh Centris 610 also supports most of the NuBus ’90 features described here.

NuBus ’90 is the 1990 proposal for revision of the IEEE standard for the NuBus (IEEE Std R1196-R-1990). The NuBus slots in the Macintosh Centris 650 and Macintosh Quadra 800 computers provide the following new features described in that proposal:

• Signals /TM2, /CLK2X, and /CLK2XEN support block transfers at double the standard rate. The Macintosh Centris 650 and Quadra 800 computers allow double-rate block transfers between NuBus cards but do not support double-rate transfers to or from the main logic board.
• Signals SB0 and SB1 support a serial bus on the formerly reserved pins A2 and C2. The serial-bus signals are bused and terminated, but the main circuit board does not drive them. (They are not connected on the Macintosh Centris 610 computer.)
• Signals /CM0, /CM1, /CM2, and /CBUSY support a cache-coherency protocol. Pins on the NuBus connector are assigned to these signals, but the Macintosh Centris 650 and Macintosh Quadra 800 computers don’t support them.

Macintosh II Introdocution

NuBus, Texas Instruments' synchronous bus definition, allows any device to become master of the system. Therefore, 80286 cards, EtherNet cards, and other intelligent interfaces may, at times, gain control of the CPU. With this architecture, the Macintosh II could run MS-DOS software, act as a smart terminal, or drive a variety of output devices. Apple's NuBus implementation includes interrupt lines from each of the slots, and has changed the size of the interface card to conform to the Macintosh II case size.