OS/360 was a batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964. OS/360 was amongst the earliest operating systems to make direct access storage devices a prerequisite for its operation.

Origins

OS/360 was developed as a family of three control programs, which increased in size as well as functionality. Initially, the single task PCP (Primary Control Program) processed jobs sequentially; the next, MFT (Multiprogramming with a Fixed number of Tasks) added multitasking, but only allowed a fixed number of concurrent tasks, each one having a preset memory allocation. Finally MVT (Multiprogramming with a Variable number of Tasks) allowed varying numbers of tasks whose memory size could change dynamically. OS/360 also introduced IBM's batch-scripting language JCL (Job Control Language).

OS/360 was late being delivered, due to a combination of organizational disarray inside IBM and lack of experience with the pitfalls of large software projects, as well as the significant technical challenges. Originally scheduled for delivery in 1965 (for the simplest versions) and 1966 (for the more complex ones), it ended up being a year late — it was not released in its first production versions until 1966 and 67 (PCP and MVT, respectively).

A family of simple alternative systems, BOS (Basic Operating System, for the smallest machines), TOS (Tape Operating System, for machines with only tape drives), and DOS (Disk Operating System), was therefore hurriedly put together to allow customers to use the new machines.

References

• Pugh, Emerson W.; Johnson, Lyle R.; Palmer, John H. (1991). IBM's 360 and Early 370 Systems. MIT Press, Cambridge, MA. (pp. 291-345)

External links

• MVS... a long history: OS/360
• Operating System/360 1965-1972