The first Prime system ran an operating system called DOS written by Bill Poduska one weekend in 1968 (see Prime FAQ).
The Prime 400 arived at RAL with Rev 13 of the Primos Operating System. Early on, Cliff Pavelin and Len Ford were primarily responsible for changes to the operating system with Graham Robinson working on the communication side. Making changes was relatively easy given that Prime gave us a copy of the source which was in Fortran. However, getting Prime to accept any of these as sensible changes to the Prime-supported product was much more difficult. Mike Greata of Prime was always pessimistic about the universal requirement for the change and the approach adopted by RAL in making the fix.
Some examples of the changes made were:
If you were unaware of Prime's future releases, it was easy to make changes which were of little use as they appeared in the next Revision of the operating system.
Rev 14 arrived early in 1978 and did not have much additional functionality required by ICF but did have a lot of performance improvements. Rev 11 had good performance and few features. Revs 12 and 13 had added a lot of functionality but with an erosion of performance. Rev 14 concentrated on removing the worst of the bottlenecks. It included a new scheduler, faster swapping of users, better overlap of disc I/O with other activities, etc. The RAL P400 on Rev 13 had 10% overlap of disc I/O with other activities while Rev 14 had closer to 75%.
A major irritant in Rev 13 was the need to insert some parameters to routines as octal numbers. Over the releases, these were gradually weeded out but even in Rev 24 released in 1997 there were still some residual routines requiring octal parameters!
During the life of the ICF, Primos went from Rev 13 to Rev 19.4 gradually adding more functionality and better security.
