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TheCray Operating System (COS) is aCray Researchoperating system for its now-discontinuedCray-1 (1976) andCray X-MPsupercomputers. It succeeded theChippewa Operating System (shipped with earlierControl Data Corporation CDC6000 series and7600 computer systems), and was the Cray main OS until replaced byUNICOS in the late 1980s. COS was delivered withCray Assembly Language (CAL),Cray FORTRAN (CFT), andPascal.

As COS was written by ex-Control Data employees, its command language and internal organization bore strong resemblance to theCDC SCOPE operating system on theCDC 7600 and before thatEXEC*8 from CDC's earlier ERA/Univac pedigree. User jobs were submitted to COS via front-end computers via a high-speed channel interface, and so-calledstation software. Front end stations were typically largeIBM orControl Data mainframes. However theDEC VAX was also a very popular front-end. Interactive use of COS was possible through the stations, but most users simply submitted batch jobs.

Disk-resident datasets used by a user program were 'local' to the individual job. Once a job completed, its local datasets would be released and space reclaimed. In order to retain the data between jobs, datasets had to be explicitly made 'permanent'.Magnetic tape datasets were also supported on Cray systems which were equipped with an I/O Subsystem.

COS also provided job scheduling and checkpoint/restart facilities to manage large workloads, even across system downtimes (both scheduled and unscheduled.)

Internally, COS was divided into a very small message-passing EXEC, and a number of System Task Processors (STP tasks). Each STP task was similar in nature to the peripheral processor programs in earlier Control Data operating systems, but since the Cray machines did not have peripheral processors, the main central processor executed the operating system code.

This list isincomplete; you can help byadding missing items.(February 2011)

While the source for version 1.13 was released aspublic domain, 1.17 is available at archive.org.^[2]

• Cray Time Sharing System
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