# XP/S4
**Wikidata**: [Q69707072](https://www.wikidata.org/wiki/Q69707072)  
**Source**: https://4ort.xyz/entity/xp-s4-q69707072

## Summary
XP/S4 is a 1993-era Intel-built supercomputer that delivered 1.5–1.75 Gigaflops (Rmax) and 2.8 Gigaflops (Rpeak) while running the OSF/1 Unix operating system. It is catalogued as TOP500 system #550 and is classified as a 56-core supercomputer.

## Key Facts
- Listed on the TOP500 list as system ID 550.
- Peak performance (Rpeak): 2.8 Gigaflops; sustained performance (Rmax): 1.5 Gigaflops (Jun–Nov 1993) and 1.75 Gigaflops (Jun 1994–Nov 1994).
- Processor core count: 56.
- Manufacturer: Intel Corporation (founded 18 Jul 1968, Santa Clara, CA).
- Operating system: OSF/1 (Open Software Foundation Unix variant).
- Instance of: supercomputer.
- Country of origin: United States.

## FAQs
### Q: What operating system did XP/S4 use?
A: XP/S4 ran OSF/1, a Unix variant developed by the Open Software Foundation.

### Q: How fast was XP/S4?
A: In 1993–1994 benchmarks it reached 2.8 Gigaflops peak and 1.5–1.75 Gigaflops sustained performance.

### Q: Who built XP/S4?
A: Intel Corporation manufactured the machine in the United States.

## Why It Matters
XP/S4 represents Intel’s early push into the high-performance computing market at a time when supercomputers were transitioning from proprietary vector designs toward massively parallel microprocessor-based systems. By combining commodity Intel processors with the open OSF/1 Unix, the system demonstrated that scalable, standards-based hardware could deliver competitive floating-point performance. Its TOP500 listing helped establish Intel’s credibility in scientific computing, foreshadowing the x86 dominance that followed with later Pentium and Xeon families. For historians, XP/S4 is a datapoint showing how OSF/1—an early attempt at a unified Unix standard—found a niche in compute-intensive environments before giving way to Tru64 UNIX and, eventually, Linux clusters.

## Notable For
- One of the earliest Intel-manufactured machines to enter the TOP500 list.
- Achieved 2.8 Gigaflops peak on only 56 cores—an impressive ratio for 1993 hardware.
- Ran OSF/1, illustrating adoption of vendor-neutral Unix in supercomputing.
- Maintained consistent Rpeak across multiple TOP500 releases, indicating stable architecture.

## Body
### Architecture and Hardware
XP/S4 is built around 56 processor cores supplied by Intel. The exact microarchitecture is not specified in the source data, but the core count and performance figures place it in the early “Pentium-era” timeframe when Intel was exploring multi-chip modules and cache-coherent SMP designs.

### Performance Trajectory
Between June 1993 and November 1994 the system’s Rmax rose from 1.5 to 1.75 Gigaflops while Rpeak stayed flat at 2.8 Gigaflops, suggesting software tuning or memory-bandwidth improvements rather than hardware upgrades.

### Software Stack
The machine shipped with OSF/1, the Open Software Foundation’s Unix reference implementation that later evolved into Tru64 UNIX. OSF/1 provided POSIX compliance, symmetric multiprocessing support, and networking services required by academic and government labs.

### TOP500 Context
System #550 on the TOP500 list, XP/S4 sat in the middle tier of early-1990s supercomputers—well below the leading vector machines but competitive among microprocessor-based clusters.