Editing Cray Operating System (section)

==Design==
As COS was written by ex-[[Control Data]] employees, its command language and internal organization bore strong resemblance to the [[CDC SCOPE]] operating system on the [[CDC 7600]] and before that [[EXEC*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-called ''station software''.  Front end stations were typically large [[IBM]] or [[Control Data]] mainframes.  However the [[DEC 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.

===List of STP tasks===
{{Expand list|date=February 2011}}

{| class="wikitable" border="1"
|-
! STP Task
! Description
|-
|Z, ZY
|Startup Prep
|-
| STARTUP
| Startup
|-
| EXP
| User Exchange Processor
|-
|MSP
|Message Processor
|-
| DQM
| Disk Queue Manager
|-
| TQM
| Tape Queue Manager
|-
| JSH
| Job Scheduler
|-
| PDM
| Permanent Dataset Manager
|-
| JCM
| Job Class Manager
|-
| SCP
| Station Call Processor
|}

While the source for version 1.13 was released as [[public domain]], 1.17 is available at archive.org.<ref>{{Cite web|url=https://archive.org/details/Cos1.17DiskImageForCray-1x-mp|title=COS 1.17 disk image for Cray-1/X-MP}}</ref>