Sequent Computer Systems

Sequent Computer Systems, Inc.
Company type	Private
Industry	Computer hardware, Computer systems
Founded	1983
Founder	Seventeen engineers and executives from Intel and one from outside Intel
Defunct	1999
Fate	Acquired by IBM
Successor	IBM
Headquarters	United States, United States
Area served	Worldwide
Products	Multiprocessing computer systems (Balance series, Symmetry series, NUMA-Q)
Parent	IBM (from 1999)

Sequent Computer Systems, Inc. was an innovative American firm specializing in advanced multiprocessing computer systems designed for high performance. Renowned for breakthroughs in symmetric multiprocessing (SMP) technology—covering hardware aspects like cache control and interrupt processing, as well as software methods such as read-copy-update—Sequent secured a prominent position within the premium UNIX server sector throughout the late 1980s and early 1990s.

Through collaboration with Oracle Corporation, Sequent emerged as a leading UNIX platform supplier. The company subsequently introduced NUMA-Q, an advanced high-end system compatible with UNIX and Windows NT, built upon non-uniform memory access (NUMA) architecture. As hardware costs fell and Intel redirected its efforts toward Itanium processors during the late 1990s, Sequent participated in Project Monterey starting in 1998, which sought to unify UNIX across diverse hardware platforms.

IBM acquired Sequent in July 1999, incorporating its technology into IBM’s server offerings while continuing to market Sequent’s hardware. Nevertheless, by May 2002, diminishing demand prompted IBM to discontinue products originating from Sequent’s portfolio. Despite this phase-out, Sequent’s technological contributions endure within data clustering solutions by PolyServe (later acquired by HP), involvement with OSDL initiatives, enhancements to IBM’s Linux kernel work, and related industry legal proceedings.

Sequent’s corporate approach centered on providing scalable multiprocessing systems tailored for enterprise clients, leveraging innovation and strategic alliances to sustain a competitive edge amid the evolving landscape of high-end servers.

History

Initially called Sequel, the company was established in 1983 by seventeen engineers and executives departing Intel following the termination of the iAPX 432 project, along with one individual from outside Intel. Their focus was on creating symmetric multiprocessing (SMP) computer systems, a then-nascent area in computer architecture.

Balance

Sequent’s first product offerings comprised the Balance 8000 (1984) and Balance 21000 (1986). Both utilized 10 MHz National Semiconductor NS32032 processors equipped with modest write-through caches linked to shared memory. The Balance 8000 accommodated up to 12 processors through six dual-processor boards, whereas the Balance 21000 supported scaling up to 30 processors using fifteen dual-processor boards.

Operating on DYNIX, a customized variant of 4.2BSD Unix, these machines competed effectively against DEC’s VAX-11/780. Their design enabled any processor to execute any process, supplemented by libraries that assisted developers in crafting applications optimized for multiprocessing environments.

Symmetry

The subsequent significant product series was the Intel 80386-based Symmetry line introduced in 1987. These models ranged from configurations with 2 up to 30 processors and featured enhancements such as a new copy-back cache mechanism alongside a broader 64-bit memory bus. In 1991, the Symmetry 2000 series incorporated multiple SCSI controllers and supported between one and six Intel 80486 processors. By 1992, the VMEbus-based Symmetry 2000/x50 model arrived featuring faster CPUs.

Throughout the late 1980s and early 1990s, Sequent transitioned its operating system from DYNIX to DYNIX/ptx, which combined elements of AT&T Corporation’s UNIX System V with features from 4.2BSD. This era saw substantial business expansion fueled by a strategic alliance with Oracle Corporation, particularly in support of their enterprise-grade database servers. In 1993, Sequent launched the Symmetry 2000/x90 alongside ptx/Cluster software that offered improved high availability capabilities and tailored integration for Oracle Parallel Server.

The Symmetry 5000 series debuted in 1994 (models SE20, SE60, SE90), utilizing 66 MHz Pentium processors and scaling up to thirty CPUs. Later enhancements included the SE30/70/100 lineup equipped with 100 MHz Pentium chips in 1995 and the SE40/80/120 models featuring 166 MHz Pentiums in 1996. Additionally, a specialized variant known as the WinServer 5000 series operated on Windows NT rather than DYNIX/ptx, targeting alternative market segments.

NUMA

Confronted with mounting competition in symmetric multiprocessing (SMP) systems and the trend toward greater microprocessor integration, Sequent redirected its efforts to stand out by adopting cache-coherent non-uniform memory architecture (ccNUMA) through the use of the Scalable Coherent Interconnect. Unlike SMP systems, NUMA allocates memory across multiple processors, alleviating common bottlenecks. This design enhanced server performance by enabling tasks to access memory situated closer to their executing processor.

In 1996, Sequent introduced the STiNG system—an acronym for Sequent: The Next Generation (with Intel inside)—which was marketed under the name NUMA-Q. This release marked a significant evolution in Sequent’s business strategy and was the final product before IBM acquired the company for more than $800 million.

Following the acquisition, IBM collaborated with Santa Cruz Operation on Project Monterey, which sought to develop a standardized Unix operating system with NUMA support across IA-32, IA-64, and POWER architectures. Although this initiative was eventually discontinued as both parties shifted focus toward Linux-based solutions, it played a role in later industry legal conflicts such as SCO v. IBM.

IBM purchase and disappearance

Struggling with its product direction, Sequent was bought by IBM in 1999 for $810 million. IBM subsequently launched several x86 servers incorporating NUMA technology, starting with the x440 in 2002, followed by the x445 in 2003 and the Itanium-powered x455 in 2004. The NUMA framework became central to IBM’s extended X-Architecture (eXA), which progressed into the fifth-generation eX5 platform by 2011, currently marketed under IBM System x.

A 2002 article from The Wall Street Journal outlined IBM’s strategic reasoning: Sequent lacked sufficient scale to challenge Sun Microsystems and Hewlett-Packard within the Unix server market. Concurrently, IBM was contending with an aging and costly server lineup, declining personal computer sales, and a reduction in mainframe revenues.

Detailed model descriptions

Sequent’s first two generations of Symmetry systems (1987–1990) demonstrated their pioneering work in multiprocessing technology.

Symmetry S-series

Symmetry S3: Positioned as a low-end solution using standard PC hardware running DYNIX 3. It incorporated a single 33 MHz Intel 80386 CPU, supported up to 40 MB of RAM, included 1.8 GB of SCSI disk storage, and provided up to 32 serial ports.

Symmetry S16: An entry-level multiprocessing system operating on DYNIX/ptx with up to six 20 MHz Intel 80386 processors each equipped with 128 KB cache. It supported as much as 80 MB RAM, 2.5 GB of SCSI storage, and featured up to 80 serial ports.

Symmetry S27: Compatible with DYNIX/ptx or DYNIX 3, this model accommodated up to ten 20 MHz Intel 80386 CPUs (each with 128 KB cache), supported up to 128 MB RAM, offered 12.5 GB disk capacity, and included up to 144 serial ports.

Symmetry S81: Running either DYNIX/ptx or DYNIX 3, it supported as many as thirty 20 MHz Intel 80386 processors (with 128 KB cache each), up to 384 MB RAM, approximately 84.8 GB of disk storage, and provided up to 256 serial ports.

Symmetry 2000 series

Symmetry 2000/40: The S2000/40 served as a low-end platform built on commodity PC components running a compatible version of DYNIX/ptx. It featured a single Intel 80486 processor at 33 MHz, supported up to 64 megabytes of RAM, offered up to 2.4 gigabytes of SCSI disk space, and included up to 32 directly connected serial ports.

Symmetry 2000/200: This entry-level multiprocessing configuration ran DYNIX/ptx and could support up to six Intel 80486 processors at 25 MHz each with a cache size of 512 KB. It allowed for up to 128 MB RAM, provided 2.5 GB of SCSI storage, and accommodated up to 80 serial ports.

Symmetry 2000/400: Operating under either DYNIX/ptx or DYNIX 3, this model included up to ten Intel 80486 CPUs running at 25 MHz with a cache size of 512 KB each. It supported as much as 128 MB RAM, contained around 14.0 GB disk storage, and had capacity for up to 144 serial ports.

Symmetry 2000/700: The high-performance variant ran DYNIX/ptx or DYNIX 3 and housed up to thirty Intel 80486 processors at a clock speed of 25 MHz each with a cache size of 512 KB. It supported up to 384 MB RAM, offered about 85.4 GB disk capacity, and included up to 256 serial ports.