Sequent Computer Systems
Sequent Computer Systems
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Sequent Computer Systems

Sequent Computer Systems, Inc. was a computer company that designed and manufactured multiprocessing computer systems. They were among the pioneers in high-performance symmetric multiprocessing (SMP) open systems, innovating in both hardware (e.g., cache management and interrupt handling) and software (e.g., read-copy-update).

Through a partnership with Oracle Corporation, Sequent became a dominant high-end UNIX platform in the late 1980s and early 1990s. Later they introduced a next-generation high-end platform for UNIX and Windows NT based on a non-uniform memory access architecture, NUMA-Q. As hardware prices fell in the late 1990s, and Intel shifted their server focus to the Itanium processor family, Sequent joined the Project Monterey effort in October 1998, which aimed to move a standard Unix to several new platforms.

In July 1999 Sequent agreed to be acquired by IBM. At the time, Sequent's CEO said its technology would "find its way through IBM's entire product field" and IBM announced it would "both sell Sequent machines, and fold Sequent's technology...into its own servers", but by May 2002 a decline in sales of the models acquired from Sequent, among other reasons, led to the retirement of Sequent-heritage products.

Vestiges of Sequent's innovations live on in the form of data clustering software from PolyServe (subsequently acquired by HP), various projects within OSDL, IBM contributions to the Linux kernel, and claims in the SCO v. IBM lawsuit.

Originally named Sequel, Sequent was formed in 1983 when a group of seventeen engineers and executives left Intel after the failed iAPX 432 "mainframe on a chip" project was cancelled; they were joined by one non-Intel employee. They started Sequent to develop a line of SMP computers, then considered one of the up-and-coming fields in computer design.

Sequent's first computer systems were the Balance 8000 (released in 1984) and Balance 21000 (released in 1986). Both models were based on 10 MHz National Semiconductor NS32032 processors, each with a small write-through cache connected to a common memory to form a shared memory system. The Balance 8000 supported up to 6 dual-processor boards for a total maximum of 12 processors. The Balance 21000 supported up to 15 dual-processor boards for a total maximum of 30 processors.

The systems ran a modified version of 4.2BSD Unix the company called DYNIX, for DYNamic unIX. The machines were designed to compete with the DEC VAX-11/780, with all of their inexpensive processors available to run any process. In addition the system included a series of libraries that could be used by programmers to develop applications that could use more than one processor at a time.

Their next series was the Intel 80386-based Symmetry, released in 1987. Various models supported between 2 and 30 processors, using a new copy-back cache and a wider 64-bit memory bus. 1991's Symmetry 2000 models added multiple SCSI boards, and were offered in versions with from one to six Intel 80486 processors. The next year they added the VMEbus based Symmetry 2000/x50 with faster CPUs.

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