1. Critical Elements of the IBM System 360 Jeff Schreibman CS585: Computer Architecture Summer 2002

2. Introduction IBM in the early 1960’s IBM’s vision for the System 360 Success of the 360

3. Critical Elements Forward and Backward Compatibility Separation Between Architecture and Implementation Integration of Scientific and Business Efficiency Extensive Use of Microprogramming

4. Forward and Backward Compatibility Family concept Compatibility throughout product line Configurable at both hardware and software levels Trade-off: performance

5. Separation of Architecture and Implementation Use of the same ISA created clear separation Modularity of architecture and implementation increased Trade-off: performance

6. Integration of Scientific and Business Efficiency Break the common construct General-purpose machine (first successful venture of its type) Booming business spurred from this Trade-off: performance (see the trend here…)

7. Extensive Use of Microprogramming Micro-programs accomplish tasks in different ways (with different instructions) CISC was needed

8. 360/370 Architecture Components Sixteen 32 bit, general purpose registers 4 double-precision (64-bit) floating-point registers Program status word (PSW) holds the PC, some control flags, and the condition codes

9. Instruction Set Format Register 0 is special when used in addressing mode (NOTE: zero is always substituted) These are covered more extensively in the next 3 slides, but here is their general format.

10. 5 Instruction Formats RR (register-register) RX (register-indexed) RS (register-storage) SI (storage-immediate) SS (storage-storage)

11. The 360/370 Instruction Formats

12. Typical IBM 360 Instructions with their Meanings

13. SUCCESS! “In the 6 years from 1965-1971, IBM’s gross income increased 2.3 times from $3.6 billion to $8.3 billion and net earnings after taxes increased 2.3 times from $477 million to $1.1 billion. In 1982, the descendants of System 360 accounted for more than half of IBM’s gross income.” (Gifford and Spector, 1987)

14. Summary IBM’s Vision Critical Elements of the IBM System 360 –Forward and Backward Compatibility –Separation Between Architecture and Implementation –Integration of Scientific and Business Efficiency –Extensive Use of Microprogramming The Result: Lasting Success!

15. Bibliography Amdahl, G. M., G. A. Blaauw, et al. (1964). “Architecture of the IBM System/360.” Readings in Computer Architecture. G. Sohi. San Fransico, California, Morgan Kaufmann: 17- 27. Gifford, D. and A. Spector (1987, April). "Case Study: IBM's System/360-370 Architecture." Communications of the ACM 30(4): 292-307. Hennessy, John. and Patterson, David. (1990). Computer Architechture: A Quantitative Approach. San Mateo, California, Morgan Kaufmann Publishers, Inc. Murdocca, M. and V. Heuring (2000). Principles of Computer Architecture. New Jersey, Prentice-Hall. Shaaban, Muhammad (2002) “Introduction to Computer Design, The Design Hierarchy, Technology Trends, Instruction Set Architecture (ISA) Characteristics and Classifications, CISC Vs. RISC.” http://meseec.ce.rit.edu/eecc550- spring2002/550-3-11-2002.ppt (Slide 57).http://meseec.ce.rit.edu/eecc550- spring2002/550-3-11-2002.ppt Shustek, K. “BUILDING SUPERCOMPUTERS,” URL: http://ed-thelen.org/comp- hist/Shustek/ShustekTour-03.html.http://ed-thelen.org/comp- hist/Shustek/ShustekTour-03.html