Difference between revisions of "SITS"

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'''SITS''' means "Small Incompatible Timesharing System".  It was a [[time-sharing]] [[operating system]] for a [[PDP-11/45]], created in the mid-1970s at [[MIT]] for running [[Logo]].
 
'''SITS''' means "Small Incompatible Timesharing System".  It was a [[time-sharing]] [[operating system]] for a [[PDP-11/45]], created in the mid-1970s at [[MIT]] for running [[Logo]].
  
Its design is vaguely reminiscent of [[Incompatible Timesharing System|ITS]]. Like ITS, there is a [[main memory]]-resident [[kernel]] [[debug]]ger; SALV for managing [[disk]]s; [[TECO]] for text editing, and [[DDT]] for debugging and running user programs. [[Process]]es can be [[PCLSR]]'ed just like in ITS.
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Its design is vaguely reminiscent of [[Incompatible Timesharing System|ITS]], with large influences from MIT's [[PDP-1-X Time Sharing System]]. Like ITS, there is a [[main memory]]-resident [[kernel]] [[debug]]ger; SALV for managing [[disk]]s; [[TECO]] for text editing, and [[DDT]] for debugging and running user programs. [[Process]]es can be [[PCLSRing|PCLSR]]'ed just like in ITS.  From the PDP-1-X it inherited capability-based security and the concept of spheres.  It has a hierarchical tree-structured file system inspired by [[Multics]].  SITS supported [[raster]] [[display]]s similar to those used with the MIT-AI Knight TV, and also a few [[vector graphics|vector]] displays.
  
 
The kernel debugger was written by Radia Perlman and was called RUG from the phrase "snug as a bug in a rug".  In addition to debugging, it can also read and write [[file]]s in the SITS [[file system]] which is how SITS is booted.  The default file name is DAZZEL, perhaps a nod to the [[Dazzle Dart]] game that was hosted on the same machine.
 
The kernel debugger was written by Radia Perlman and was called RUG from the phrase "snug as a bug in a rug".  In addition to debugging, it can also read and write [[file]]s in the SITS [[file system]] which is how SITS is booted.  The default file name is DAZZEL, perhaps a nod to the [[Dazzle Dart]] game that was hosted on the same machine.
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Originally Logo was implemented in [[assembly language]] on the PDP-10. In order to provide a computer system dedicated to educational use, it was adapted for the PDP-11. The first milestone in this direction was the completion in 1973-1974 of a dedicated timesharing system running 11LOGO.
 
Originally Logo was implemented in [[assembly language]] on the PDP-10. In order to provide a computer system dedicated to educational use, it was adapted for the PDP-11. The first milestone in this direction was the completion in 1973-1974 of a dedicated timesharing system running 11LOGO.
  
The was not an entirely satisfactory solution because of the inability of the system to be self-maintaining or to run other languages or special purpose jobs (like a [[simulation]] environment or an educational real-time game). During 1974-1975, our programming staff, under the direction or R. Lebel, completed the design and implementation of a general purpose multi-language timesharing system for the [[PDP-11/45]]. The SITS timesharing system was developed to provide an environment suitable for running Logo and other PDP-11/45 programs. It incorporates a [[Multics]]-like tree structured file system including (potentially) full access control. It also provides unique capabilities for running programs as multiple process systems, rather than the more common single process approach, and the ability for each user to run many [[job]]s simultaneously. The system include provisions for using both the older refreshed [[display]]s and our new [[raster]] displays.
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The was not an entirely satisfactory solution because of the inability of the system to be self-maintaining or to run other languages or special purpose jobs (like a [[simulation]] environment or an educational real-time game). During 1974-1975, our programming staff, under the direction or R. Lebel, completed the design and implementation of a general purpose multi-language timesharing system for the PDP-11/45. The SITS timesharing system was developed to provide an environment suitable for running Logo and other PDP-11/45 programs. It incorporates a [[Multics]]-like tree structured file system including (potentially) full access control. It also provides unique capabilities for running programs as multiple process systems, rather than the more common single process approach, and the ability for each user to run many [[job]]s simultaneously. The system include provisions for using both the older refreshed [[display]]s and our new [[raster]] displays.
 
</blockquote>
 
</blockquote>
  
When the SITS PDP-11/45 was decommissioned from the Logo group, it was donated to what became the Concourse Computer Center.
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When the SITS PDP-11/45 was decommissioned from the Logo group, it was donated to what became the Concourse Computer Center. It did not continue running SITS due to instability problems.  Instead the computer ran [[Unix Seventh Edition|UNIX V7]], later 2[[BSD]], and was placed on the [[Chaosnet]].
It did not continue running SITS due to instability problems.  Instead the computer ran [[Unix Seventh Edition|UNIX V7]],
 
later 2[[BSD]], and was placed on the [[Chaosnet]].
 
  
 
=== Preservation status ===
 
=== Preservation status ===
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* [[KB11-A CPU]] with [[KT11-C Memory Management Unit]]
 
* [[KB11-A CPU]] with [[KT11-C Memory Management Unit]]
* 128K [[core]] memory
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* 128K [[core memory]]
 
* EAE [[PDP-11 Extended Instruction Set]]
 
* EAE [[PDP-11 Extended Instruction Set]]
 
<!-- ??? In the -11/45, the EAE is part of the basic CPU -->
 
<!-- ??? In the -11/45, the EAE is part of the basic CPU -->

Revision as of 16:50, 19 August 2021

SITS means "Small Incompatible Timesharing System". It was a time-sharing operating system for a PDP-11/45, created in the mid-1970s at MIT for running Logo.

Its design is vaguely reminiscent of ITS, with large influences from MIT's PDP-1-X Time Sharing System. Like ITS, there is a main memory-resident kernel debugger; SALV for managing disks; TECO for text editing, and DDT for debugging and running user programs. Processes can be PCLSR'ed just like in ITS. From the PDP-1-X it inherited capability-based security and the concept of spheres. It has a hierarchical tree-structured file system inspired by Multics. SITS supported raster displays similar to those used with the MIT-AI Knight TV, and also a few vector displays.

The kernel debugger was written by Radia Perlman and was called RUG from the phrase "snug as a bug in a rug". In addition to debugging, it can also read and write files in the SITS file system which is how SITS is booted. The default file name is DAZZEL, perhaps a nod to the Dazzle Dart game that was hosted on the same machine.

AI memo 356 "Logo Progress Report 1973-1975" has this:

Originally Logo was implemented in assembly language on the PDP-10. In order to provide a computer system dedicated to educational use, it was adapted for the PDP-11. The first milestone in this direction was the completion in 1973-1974 of a dedicated timesharing system running 11LOGO.

The was not an entirely satisfactory solution because of the inability of the system to be self-maintaining or to run other languages or special purpose jobs (like a simulation environment or an educational real-time game). During 1974-1975, our programming staff, under the direction or R. Lebel, completed the design and implementation of a general purpose multi-language timesharing system for the PDP-11/45. The SITS timesharing system was developed to provide an environment suitable for running Logo and other PDP-11/45 programs. It incorporates a Multics-like tree structured file system including (potentially) full access control. It also provides unique capabilities for running programs as multiple process systems, rather than the more common single process approach, and the ability for each user to run many jobs simultaneously. The system include provisions for using both the older refreshed displays and our new raster displays.

When the SITS PDP-11/45 was decommissioned from the Logo group, it was donated to what became the Concourse Computer Center. It did not continue running SITS due to instability problems. Instead the computer ran UNIX V7, later 2BSD, and was placed on the Chaosnet.

Preservation status

Only a few snapshots of SITS exist on ITS backup tapes from the AI Lab PDP-10.

  • SITS version 1146 from October 1975;
  • NSITS versions 111, 112 from December 1975;
  • A set of disk images from May 1978 with an unknown SITS version.

Hardware support

This is the list of supported, or actually required hardware for SITS version 1146: