TSS/360

The IBM Time Sharing System TSS/360 was an early time-sharing operating system which ran on a special model of the System/360 line of mainframes, the Model 67. Introduced in 1967, it implemented a number of novel features which eventually saw daylight in more popular systems such as Multics and VM/CMS.

Novel characteristics

TSS/360 was the first implementation of tightly-coupled symmetric mainframe multiprocessing. A pair of Model 67 mainframes shared a common physical memory space, and ran a single copy of the kernel (and application) code. An I/O operation launched by one processor could end and cause an interrupt in the other. The Model 67 used a standard 360 instruction called Test and Set to implement locks on code critical sections.

TSS/360 also implemented Virtual Memory and Virtual Machines using position-independent code. [cite book
author = John R. Levine
title = Linkers and Loaders
chapter = Chapter 8: Loading and overlays
chapterurl = http://darcs.olsner.se/Linker/linker-book/linker08.html
month = October
year = 1999
publisher = Morgan-Kauffman
location = San Francisco
pages = 170–171
isbn = 1-55860-496-0 ]

TSS/360 was also unique in implementing a Table Driven Scheduler — a user-configured table whose columns were parameters such as current priority, working set size, and number of timeslices used to date. The kernel would refer to this table when calculating the new priority of a thread.

As was standard with operating system software at the time, TSS/360 customers (such as General Motors Research Laboratories) were given full access to the entire corpus of Operating System code and development tools. User-developed improvements and patches were frequently incorporated into the official source code.

TSS/360 failed primarily due to performance and reliability problems, and lack of compatibility with OS/360. IBM attempted to develop it on a very aggressive schedule with a large staff of programmers to compete with Multics. By 1967, it had become evident that TSS was suffering from the same kinds of delays as OS/360. Several other groups had developed less ambitious, more successful time sharing systems for the 360/67, notably CP-67 at IBM's Cambridge Scientific Center, an early virtual machine monitor which evolved into VM/370, and MTS at the University of Michigan. In the early 1970s, IBM cancelled the TSS project and instead put effort into the Time Sharing Option (TSO), a time-sharing monitor for OS/360. However, a TSS/370 system was quietly made available for a while to existing TSS/360 customers, as an interim measure.

See also

* History of operating systems
* Operating systems timeline

References

Further reading

* cite book
last = Pugh
first = Emerson
coauthors = Lyle R. Johnson, John H. Palmer
title = IBM's 360 and Early 370 Systems
publisher = MIT Press
date = 1991
location = Cambridge MA
pages = 362–265, 596
isbn = 0-262-16123-0 Describes the origin and schedule problems of TSS.
* cite book
last = Brooks
first = Frederick P.
title = The Mythical Man-Month
publisher = Addison-Wesley
date = 1995
location = Reading MA
isbn = 0-201-83595-5 Describes the "second system syndrome" that affected TSS.