SBus
| Company type | Computer bus architecture |
|---|---|
| Industry | Computer hardware |
| Predecessor | VMEbus |
| Founded | 1989 |
| Founder | Edward H. Frank, James D. Lyle |
| Fate | Became obsolete after transition to PCI standard |
Area served | SPARC-based computer systems |
| Products | Computer bus architecture for expansion cards |
SBus refers to a computer bus architecture predominantly utilized in numerous SPARC-based systems produced by Sun Microsystems and other manufacturers throughout the 1990s. Launched by Sun in 1989, it succeeded the older VMEbus technology employed in their early SPARC and Motorola-based platforms. Following Sun’s decision to open the SPARC architecture in the early 1990s, SBus was formalized as IEEE-1496. By the year 1997, Sun had started transitioning to the Peripheral Component Interconnect (PCI) standard, which eventually led to SBus becoming obsolete.
The initial third-party SBus expansion cards appeared in 1989, introduced by Antares Microsystems. These included devices such as Ethernet adapters, SCSI host controllers, parallel interfaces, and serial communication ports.
Edward H. Frank and James D. Lyle were responsible for creating the SBus specification; they later authored a detailed technical manual in 1992 and established Troubador Technologies. To facilitate external hardware development, Sun also distributed developer kits to third-party manufacturers.
At its height, more than 250 companies were featured in the SBus Product Directory, which was renamed the SPARC Product Directory in 1996.
SBus was engineered specifically for SPARC CPUs to streamline compatibility across platforms. It utilizes a big-endian 32-bit address and data bus operating between 16.67 and 25 MHz, achieving data transfer speeds up to 100 MB/s. The bus architecture supports up to eight bus masters and an unlimited number of slave devices, each assigned a 28-bit address space equivalent to 256 MB.
With the arrival of the 64-bit UltraSPARC processors, SBus was upgraded to handle 64-bit doubleword transfers at speeds reaching 200 MB/s, while preserving backward compatibility with earlier implementations.
The physical dimensions of SBus cards were compact—83.82 mm in width and 146.7 mm in length—enabling three expansion slots within the slim "pizza box" chassis of the SPARCstation 1. The design also accommodated wider cards spanning two or three slots as well as double-height configurations.
Initially designed to function both as a system bus and peripheral interface facilitating low-latency memory access,[1] SBus rapidly evolved into primarily serving as an input/output bus after CPU and memory performance surpassed its capabilities. Within a year of SBus’s debut, some Sun systems adopted MBus technology for CPU-memory interconnection purposes.
See also
External links
- SBus Specification at Bitsavers
- 15205-2000 - ISO/IEC 15205:2000 (IEEE Std 1496-1993) SBus -- Chip and Module Interconnect Bus
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