1. IBM OS/360 Andrew Kennedy Kyle Hunter Mehdi Tabdili Chase Crabtree

2. System/360 Design Goals Extend to Commercial, Scientific, and Real Time applications General method for using I/O devices that differed in data rate, access and function Enable asynchronous operation of circuit, storage and input/output components with respect to each other (timesharing)

3. System/360 Series Overview Noteworthy Models: –25 ~ Small, specialized applications –67 ~ Virtual Memory, TSS/360  CP-67 –85 ~ Cache Memory 3 Operating Systems: –DOS/360 –OS/360 –TSS/360

4. OS 360 Principal Control Program (PCP) Almost all operating systems prior to the OS/360 ran using stacked job batch processing (Pugh et al., 1991). A single job ran at a time until completion. Scheduler level-1 – Allocated memory to one job at a time. Supervisor level-1 – Initiated the execution of each job in turn.

5. OS/360 MFT and MVT MFT –Could run a fixed number of prioritized jobs concurrently. –Memory was divided into partitions. –One job resided in each partition of memory. –Supervisor level-2 – Supported the partitioning of memory and multiprogramming among the partitions. –Scheduler level-2 – Permitted job inputting with concurrent program execution. Established a job queue, and initiated the execution of tasks according to priorities. MVT –Allocated dynamic memory partitions for jobs which could grow bigger or smaller during execution. –Supervisor level-3- Supported the partitioning of memory dynamically. Reallocated memory when were jobs completed. –Scheduler level-2

6. Time-Sharing Option (TSO) IBM did significant work on timesharing systems in the 1960’s. Their experiments dealt with new concepts such as the virtual machine. The Time-Sharing System (TSS) operating system was released in 1967 but because it was so expensive and many of IBM’s customers used OS/360 it was abandoned. TSO software was released to run on OS/360 MVT.

7. What Was Done Right with IBM OS/360 Each part was tested separately to make sure it was working properly. Introduction of Multi- Programming Job Control Language (JCL) TSO and “Time Sharing” Easier Input/Output operation

8. What Was Done Wrong with IBM OS/360 Managerial Differences caused a long delay before its release. Many Bugs at the time of its release Complicated Installation process.

9. IBM OS 360 Deadlock Solutions Devices, volumes, and memory are allocated in order on a per-job-step basis When Temporary file space can cause deadlocks, operator intervenes and kills a job Combination of Prevention and Detection/Removal

10. Commercially Successful IBM’s OS/360 was very flexible in a way such that it was built to be able to handle any type of commercial or scientific task. Ex: A specific model was built for the North America missile defense.

11. Economically Successful “$5 Billion Gamble” Within four weeks, IBM had 1,000 orders for the computers and associated peripherals. Two years later the company had amassed 9,000 orders (Goff, 1999). They made the $5 billion back and made much more over the years.