IBMs VM Operating System Keith Starling Overview Released

IBM’s VM Operating System Keith Starling

Overview • Released by International Business Machines (IBM) in 1972 • Each login creates a virtual machine (guest) – Each guest can run another Operating System – Ideal for development and migration • Updated for 64 -bit and Linux in 2000

Control Program • Responsible for device mapping – Real – Shared – Simulated • Dispatches guests to Central Processing Units (CPUs)

Modern VM Usage (International Business Machines, September 2004)

Processor Modes • Two processor modes – Supervisor – Problem • Set in the Program-Status Word, bit 15 • Determines which instructions can be run – Unprivileged – Semiprivileged – Privileged

Multiprocessing • Supported at multiple levels – Real multiprocessing • VM itself runs on multiple processors – Virtual multiprocessing • Each guest can have up to 64 virtual CPUs

Memory Model (Geiselhart et al. , May 2003)

CPU Scheduling • Two time slices – Elapsed Time Slice – Dispatch (Minor) Time Slice • Four Classifications – Class 0 – Immediate Processor Access – Class 1 – Interactive Tasks – Class 2 – Non-Interactive Tasks – Class 3 – Resource-Intensive Tasks

CPU Scheduling (Cont. ) • Three lists – Dormant – Eligible – Dispatch • Processes compete for CPU for their Elapsed Time Slice – Run on CPU for Dispatch Time Slice – Compete according to priority

CPU Scheduling (Cont. ) • Determining Elapsed Time Slices – Class 1 Elapsed Time Slice starts at 1. 2 sec • Increases or decreases as system runs – (50 ms < t < 16 sec) – Class 0 Time Slice is 6 times Class 1 – Class 2 Time Slice is 8 times Class 1 – Class 3 Time Slice is 48 times Class 1 • Dispatch Time Slice determined at initialization

CPU Scheduling (Cont. ) (Geiselhart et al. , May 2003)

Summary • Robust Environment for OS development and clustering • Attachment to IBM’s z/Architecture allows hardware to perform or optimize some OS tasks • Unfortunately, attachment to mainframe hardware increases price

Bibliography • • “IBM: About the z/VM Operating System. ” URL: http: //www. vm. ibm. com/overview/ “IBM: VM History and Heritage References. ” URL: http: //www. vm. ibm. com/history/ Geiselhart, G. , Dupin, L. , George, D. , van der Heij, R. , Langer, J. , Norris, G. , Robbins, D. , Robinson, B. , Sansoni, G. , Thoss, S. (May 2003). “Linux on IBM e. Server z. Series and S/390: Performance Measurement and Tuning, IBM Redbook. ” URL: http: //www. redbooks. ibm. com/redbooks/pdfs/sg 246926. pdf International Business Machines (May 2004). “z/Architecture Principles of Operation. ” URL: http: //publibz. boulder. ibm. com/epubs/pdf/dz 9 zr 003. pdf International Business Machines (September 2004). “Getting Started with Linux on z. Series: Version 5 Release 1. 0. ” URL: http: //publibz. boulder. ibm. com/epubs/pdf/hcsx 0 b 00. pdf Starling Jr. , Robert Keith. Personal Interview. November 19, 2005. WRAL: Local Tech Wire (July 27, 2005). “Introducing the z 9: IBM Unveils $1. 2 Billion Successor to Its T-Rex Mainframe. ” URL: http: //www. localtechwire. com/article. cfm? u=11904