NuBus
| Company type | Computer bus standard |
|---|---|
| Industry | Computer hardware |
| Founded | 1978 |
| Founder | Massachusetts Institute of Technology (MIT) |
| Fate | Mostly obsolete, except in certain embedded applications |
| Headquarters | United States |
| Products | 32-bit parallel computer bus |
NuBus () is a 32-bit parallel computer bus initially created at the MIT during 1978–1979 as part of the NuMachine workstation initiative. It was officially recognized as an IEEE standard in 1987. Western Digital was the first to fully implement NuBus for their NuMachine and the Lisp Machines Inc. LMI Lambda. The bus was subsequently integrated into Lisp systems by Texas Instruments (TI Explorer) and served as the primary expansion interface for Apple Computer. A related design, NeXTBus, was developed by NeXT. Presently, NuBus is mostly obsolete except within certain embedded applications.
Architecture
Unlike early microcomputer buses such as the S-100, which connected directly to CPU pins and power lines and were tied to specific hardware architectures, NuBus was engineered to be independent of processor type and system architecture, promoting wider adaptability.
At a time when 8- or 16-bit buses dominated, NuBus offered a 32-bit backplane, positioning it as a forward-compatible solution anticipating broad adoption of 32-bit technology. It did not impose assumptions about processor endianness or signaling protocols, enabling any compliant NuBus card to function on any NuBus system provided the appropriate device driver was available.
To facilitate ease of installation, NuBus incorporated an identification mechanism allowing cards to automatically recognize themselves during system startup, eliminating the need for manual configuration. This early form of plug-and-play contrasted with buses like ISA, which required users to manually assign drivers and system resources.
However, this increased flexibility introduced greater design complexity and expense for hardware manufacturers. Unlike simpler buses that interfaced directly with CPU-specific I/O components, NuBus cards demanded an additional controller chip to translate signals into a platform-neutral format. While this approach is common today, during the 1980s it was regarded as an expensive and overly complex solution.
Implementations
The NuBus standard was formalized by the IEEE in 1987 as IEEE 1196, utilizing a standard DIN 41612 96-pin connector arranged in three rows. Operating at a 10 MHz clock speed, it achieved peak burst data rates of up to 40 MB/s with typical throughput ranging from 10 to 20 MB/s. The later NuBus 90 variant doubled the clock frequency to 20 MHz, increasing burst transfer rates to approximately 70 MB/s and average speeds near 30 MB/s.
Commercially, NuBus originated with the Western Digital NuMachine and made its production debut through their licensee, Lisp Machines, Inc., via the LMI-Lambda Lisp Machine. Following Western Digital's divestment of the project to Texas Instruments in 1984, the technology was incorporated into TI's TI Explorer Lisp Machine and later featured in the S1500 multiprocessor UNIX system (1986). Both Texas Instruments and Symbolics developed Lisp Machine expansion boards utilizing NuBus (TI MicroExplorer and Symbolics MacIvory) as co-processor solutions for Apple's Macintosh computers, including Mac II and Quadra models.
Apple adopted NuBus for its Macintosh II lineup, aligning with its vision of plug-and-play functionality designed to enhance user convenience. The bus became standard across professional Mac II series systems from the late 1980s onward and was upgraded to NuBus 90 starting with the Macintosh Quadra models through the mid-1990s. Initial Quadra models supported the full 20 MHz speed only between two slots due to motherboard constraints; this limitation was addressed in subsequent models like the 660AV and 840AV. This improved controller design persisted into Apple's first-generation Power Macintosh 6100, 7100, and 8100 computers before Apple transitioned to Intel's PCI architecture. Apple’s implementation featured pin-and-socket connectors on card backs rather than conventional edge connectors secured by screws, streamlining installation. Additionally, Apple systems supplied a continuous +5 V "trickle" power line allowing functions such as phone line monitoring while powered down—an unofficial extension beyond the original NuBus specification.
NeXT Computer also employed NuBus in their hardware but utilized a unique printed circuit board layout. Outside these uses, NuBus experienced limited adoption and declined rapidly following Apple's shift to PCI in the mid-1990s.
See also
References
External links
- Macintosh NuBus development guide
- Collection of NuBus card images at applefritter