NuBus
NuBus is a 32-bit parallel bus that was originally developed at MIT as part of the NuMachine Workstation project and was used at times by Apple Computer , NeXT Computer and Texas Instruments . It is hardly used nowadays.
NuBus architecture
NuBus was a considerable step forward compared to other interfaces of its time. When most bus systems were still 8 bits wide (including the computers in which they were used), it was decided to introduce a 32-bit interface on the NuBus, as it was clear that the market would develop in this direction.
The NuBus worked relatively independently of the processor itself. Most bus systems until now were simple lines that went from the CPU into the backplane . This meant that the expansion cards had to comply with the data standard of the processor (e.g. Little Endian ). This is different with the NuBus. The expansion cards should be able to run in every NuBus computer, provided that a suitable device driver is available.
So that it is possible to select a suitable device driver, the NuBus uses an ID scheme to identify the expansion cards at startup. In addition, the user no longer needs to configure the system as was the case with other systems of the time. For example, with the ISA bus, not only must the driver of the expansion card be selected, but memory areas and interrupts of the card must also be specified. The NuBus does not expect such a configuration, making it one of the first examples of a plug and play architecture.
Although the NuBus simplified the handling of hardware changes in many areas, the development of expansion cards became more complicated for manufacturers. In order to establish compatibility, each expansion card had to accommodate a corresponding NuBus controller chip, which increased the manufacturing costs of the expansion cards. While such technology is hard to imagine today, the NuBus was viewed as complex and expensive in the 1980s.
NuBus applications
The NuMachine was never published, but Texas Instruments took over the technology in 1980 and later standardized it as IEEE 1196 . This version used a three-row 96-pin connector that is also used in other bus systems such as VME and PCI . A system with a 10 MHz bus clock could achieve a maximum data rate of 37.5 MB / s with burst transfers (or an average of approx. 10 to 20 MB / s). In a later change, NuBus90 , the clock rate was increased to 20 MHz in order to accelerate the data rate to a maximum of approx. 75 MB / s (average approx. 30 MB / s).
NuBus was first in the Lambda Lisp Machine of LMI used. Texas Instruments licensed the design of the LMI Lambda Lisp Machine and released its own variant, the TI Explorer . The LMI Lambda was based on the design work of the MIT NuMachine and the MIT Lisp Machine. A short time later, in 1986, Texas Instruments used the NuBus in its S1500 multiprocessor UNIX system .
Apple Computer then selected the NuBus for the Macintosh II project because it fitted perfectly into Apple's “easy to use” philosophy thanks to its Plug-n-Play design. This was used in most Macs between the late 1980s and into the 1990s.
NuBus90 was first used in the Macintosh Quadras . The first Quadras only supported the 20 MHz variant when two expansion cards were communicating with each other, as the motherboard controller was not upgraded. This was later changed in the 660AV and 840AV models and also built into the first PowerMac models. Apple's implementation also offered a permanent +5 V line so that expansion cards can perform additional tasks (e.g. call monitoring of the telephone line) while the computer was switched off. This change was not provided for in the NuBus standard.
NuBus was also used by NeXT Computer , but with a different layout than the printed circuit board . NuBus was not widely used when it was replaced by the PCI bus in the mid-1990s .
See also
Web links
- NuBus specifications ( PDF; 5.28 MB)