IBM’s OS/2

by

Chris Axford

Chris Evans

Elizabeth McGinnis

Erik Swensson

HISTORY

• IBM and Microsoft partner to make DOS replacement

• 1987 OS/2 version 1.0

• 1989 OS/2 version 1.2

• 1994 OS/2 Warp

Hardware Platforms and Devices

• Earliest version used Intel’s 80286 and 80386

• OS/2 Warp has expanded hardware compatibility

• Communication Devices

• 2 MB RAM

User Interface

• OS/2 version 1.0 used command line interface

• OS/2 version 1.1 provided Presentation Manager

Process Control Block

• Standard Format

• Traditional Aspects– Pointer– Process ID– Process State– List of Open Files– Program Counters and Registers

Multitasking

• Multiple threads per process (user and kernel)

• Standard information– Thread ID– Stack– Processor registers– Dispatch state– Priority

Process Communication and Synchronization

• Shared Memory

• Pipes

• Queues

• Semaphores– System Semaphores– RAM Semaphores

Scheduling

• Multilevel Queue Scheduling Algorithm

• 4 Priority groups– Time Critical, Server, Regular, Idle– 32 Queues for each group: total– Each Queue uses Round Robin– Priority Boasts Possible

Memory Management

• Memory Protection

• Virtual Memory and LRU Algorithm

• Memory Segment Sharing

• Memory Size Changes

FAT File System• Singly-linked cluster implementation of disk blocks

• Fixed size root directory

• Advantages

• Disadvantages

Layout of the 32 bytes in a directory entry in a FAT system. Source: http://www.edm2.com/0411/hpfs1.html

HPFS – High Performance File System

An HPFS file entry

Length of file

File attributes

Pointer to HPFS structure

Date/ Time stamp

Usage count

Length of file (up to 254 characters)

Pointer to next level in structure

•Why the need for HPFS?

•Balanced Tree Structure to store files

•Advantages to FAT

•Disadvatages to FAT

In Conclusion…