1. Mainframe Overview  - “If all the mainframes disappear, it would be the end of Western Civilization” Martin Hopkins - “What on earth is a mainframe” David Stephens Available online at google books - On Website: Mainframe Evolution paper from Research Mainframe Concepts Textbook

2. Why a mainframe? - Data Integrity - Throughput and Capacity - Response Time..Especially under heavy loads - Disaster recovery - Usability…?? - Reliability & Availability - Audit and recording - Security

3. Why not a mainframe? - Money Hardware Costs Software licensing People costs - People More people More training/person People Shortage==> higher salaries/person

4. Problems to leave the mainframe… Is it there only for historical reasons? - Buy the new hardware - Buy new software - REWRITE existing applications … “dusty deck” syndrome - Gain experience with new environment Operations and User training - Establish new processes and procedures - Function testing on duplicate workloads - Stress testing “The devil you know”

5. Other Mainframe Considerations - Cloud computing As a provider of virtual hardware, platforms (HW + OS + subsystems), and applications e.g. email, disaster recovery - Local environment Overload conditions Workload variations e.g.Time of day, April 15 Disaster situations..ability to adjust Expansion..physical or logical (people) - Mobile Computers are increasing use of Mainframes

6. Mainframe Workloads - Batch Time Scheduled..e.g Overnight Usually low priority during workday – done in background -Transaction processing Usually “dumb” terminal to mainframe... PC simulates terminal Usually 3270 data-stream but can enhance if server and PC agree Servers in a client-server environment e.g. The Web 2 tier or 3 tier designs Where does application reside for 2 tier - On PC.. quicker response but maintenance headache - On Server.. maintainable, more secure - Software development (System and Application programs)

7. Workloads that may not be the best for a Mainframe - Number Crunching - Graphics - Interactive games User interaction e.g. mouse, keystroke Give to Caesar the things the things that are Caesar’s

8. A little of mainframe history -1950s and 1960s many mainframe architectures, GE, RCA, DEC, UNIVAC all fail various reasons Amdahl and Fujitsu – uniprocessor versus SMP architecture -Technology jump i.e from Bipolar to CMOS… from amps to FETs… heat the big issue Number Crunching – parallel computation

9. © 2013 IBM Corporation 9 Communications – TCP/IP Diagram

10. A little bit of architecture -See fig 1 and 2 Explain Processor, multiprocessor Channels, Control Units (CUs) Multiple CU’s per channel Multiple Channels to each CU Multiple CU for each device e.g. 2 tailed switch PR/SM Coupling Facility -Now on to the z Architecture

11. Workload Summary - Number Crunching - Batch - Servers for Networks: Transaction processing The Web - Software development (System and Application programs)