IBM OS/2 CS450 Section 2 5:00PM Perpetrators: © Dario Berini, Derek Cole, Drew Hayes, Leigh Johann, Matt Kesler

Overview History and Advancements Processor modes and privileged instructions CPU Scheduling and thread states Symmetric Multi-Processing Threading Data structures for file and memory management

History Co-developed by IBM and Microsoft Program Manager Version History – – – Warp End of the Road

Advancements Multitasking Environment – 1987 Leveraged new processor technology –Intel High Performance File System (HPFS) Processor capable SMP in 1993 Universal Client -1996

Shortcomings Microsoft designed code through version 1.3 Lack of device drivers Poor marketing strategy from the beginning –IBM did not want to enter the software business Support for OS/2 stops December 2006

Processor Modes Intel –Capable of 2 modes Provided additional capabilities with highly limited functionality Not reliable under OS/2 1.0 Later versions of OS/2 and the x86 microprocessor improved the computing experience.

Privileged Instructions Intel Specification for 80x86 –4 levels or “Rings” Ring 0 - Most Privileged - Supervisor mode Ring 1 - Not used by OS/2 Ring 2 - “Privileged user mode” Ring 3 - Least Privileged - User mode –Additional Registers Descriptor Tables (GDT, LDT)

Scheduling OS/2 uses different scheduling mechanisms for Ring 0 and Ring 3 Each thread has: –State Running, Ready, or Blocked –Priority Classes Idle, Regular, Foreground Server, or Time-critical Classes + Delta , used to relatively distinguish threads –TC + 31

Scheduling cont. Ring 3 –Uses priority based scheduling with pre-emption –Time slices are usually 32 milliseconds Ring 0 –Still have priorities, but no time slices –Only hardware interrupts can pre-empt Ring 0 threads –Additional attribute: context (mode) Determines what APIs are available to the thread Init mode, Interrupt mode, and Kernel mode

Symmetric Multiprocessing Architecture for multiple CPUs Ability to complete individual processes simultaneously Versions 2.11 and Warp Version 4 Spinlocks implement mutual exclusion DosCreateSpinLock, DosAcquireSpinLock, DosReleaseSpinLock, DosFreeSpinLock

Threading Multithreaded Ration of threads to processes is M:1 Preemptive multitasking

File Management Data Structures HPFS B-Tree FNODEs ALNODEs FNODE Extended Attributes Control and Access History Information 15 characters of name Length of File Up to 8 Extents Pointer to Extent Length of Run Pointer to Beginning of File File

Memory Management Data Structures Offers 32-bit linear memory address space Stored as pages Memory Blocks (Memory Data Structure) Memory Block Consists of One or More Memory Pages Sub-allocation of Memory Space Memory Commitment Memory Access