TSS (operating system)

The IBM Time Sharing System TSS/360 is a discontinued early time-sharing operating system designed exclusively for a special model of the System/360 line of mainframes, the Model 67. Made available on a trial basis to a limited set of customers in 1967, it was never officially released as a supported product by IBM. TSS pioneered a number of novel features, some of which later appeared in more popular systems such as MVS. TSS was migrated to System/370 and 303x systems, but despite its many advances and novel capabilities, TSS failed to meet expectations and was eventually canceled. The Resident Supervisor of TSS/370 was used as the basis for a port of UNIX to the IBM mainframe. TSS/360 also inspired the development of the TSS/8 operating system.

TSS/360 was one of the first implementations of tightly coupled symmetric 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.

It also implemented virtual memory and virtual machines using position-independent code.

TSS/360 included an early implementation of 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. This later appeared in systems as diverse as Honeywell CP-V and IBM z/OS.

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 source of the operating system code and development tools. User-developed improvements and patches were frequently incorporated into the official source code.

TSS provides users a command-line interface. Users interact with the command system. The command format consists of Command_Name[ operands]. The command name is one to eight characters without imbedded blanks. The operands are optional depending on the command, and must be separated from the command name by at least one blank. Multiple operands should be separated by TAB characters or commas. Command lines can be continued by typing a hyphen ("-") at the end of the line to be continued and typing the continuation at the beginning of the next line. Multiple commands can be written on a line by separating them with semicolons (";"). Comments are allowed in command lines, separated from the command with a semicolon and included in single quotes ("'"). Operands can be either positional or keyword, with the format "keyword=value".

System commands are divided into seven categories:

TSS provided an early implementation of position-independent code, the ability to have different processes run a single copy of an executable possibly mapped to a different virtual addresses in each process.