1. OS/2 Warp Chris Algire Jonathan Depner Daniel Kvitko Jason Shifflett
Ryan Slominski

2. Introduction
OS/2 was a revolutionary operating system when it was introduced
The 1st to do the following:
Break the 640KB memory barrier
Support 32-bit
Support multitasking on the desktop
Automatically detect deadlocks
IBM and Microsoft
Project was a collaboration between IBM and MS
Partnership led to OS/2’s demise
Microsoft’s OS proved to be easier to use
Since the partnership between the two companies lasted even after Microsoft left the project, IBM was forced to include support for Microsoft’s OS with OS/2
As a result, most Wintel machines today can operate using OS/2
Current use
OS/2 evolved to OS/2 Warp 4 and today is in use in corporate environments due to its stability which rivals that of Unix

3. Processor Info Intel Architecture OS/2 Warp utilizes modes 0, 2, 3
Four processors modes, 0-3, where zero has highest privilege
OS/2 Warp utilizes modes 0, 2, 3
Mode 0
Kernel mode
Unrestricted direct access to hardware
Mode 2
Restrictive kernel mode
Limited direct access to output devices
Mode 3
User mode
No direct access to hardware; higher privileged modes must handle hardware access on behalf
OS/2 Warp supports uniprocessing and symmetric multiprocessing

4. File Structures
Native File System: High Performance File System (HPFS)
File Structures: Fnode, Run, B+ Tree
Fnode-run representation
B+ tree representation with Fnode as root

5. Memory Management 32-bit Flat memory model Max 512 MB per process
Fixed size 4K pages
Backwards compatible 16-bit

6. Memory Data Structures
Page Table Directory (bits 22 – 31)
Page Table (bits 12 – 21)
Page Frame (bits )
Hard Disk
Main Memory PT
PTD PF
Physical Location PT PT

7. Scheduling Preemptive-Priority Round Robin
Four Categories of Priorities
Time Critical
TimeSlice 8 milliseconds , 8 milliseconds
Server Class
TimeSlice 32 milliseconds , 248 milliseconds
Regular Class
Idle Class
Priority Increases every 3 seconds
Command Prompt
PSTAT
Config.sys file commands
MAXWAIT = nnn
TIMESLICE = x, y

8. Synchronization OS/2 implements 3 basic control structures:
semaphores
queues
pipes
OS/2 primarily uses the semaphore
Two types of semaphores:
RAM semaphore
System semaphore

9. Synchronization (cont.)
RAM Semaphore
Located in the process’ main memory space
Accessible by all threads
Faster than system semaphores in access time
System Semaphore
Stored outside the address space of any process
Slightly slower than RAM semaphores
Can be used as counting semaphores

10. Handling deadlocks in OS/2
Prevention
Round-robin scheduling algorithm
dynamic time quantum for each process
Each process is assigned a priority level
The round-robin algorithm first services highest priority processes then the lower level priority processes
Semaphores
Avoidance
Avoiding race conditions through the following mechanisms:
Memory over-commitment – the OS allocates more memory to the process through swapping lower level priority processes out of memory into disk.
Implements least-recently used algorithm to swap processes in and out of disk.
Detection
Each process has a unique signal handler

11. Future of OS/2 warp Lacks device support E- commerce
OS/2 warp 4 is the last forcible version
Platform independent applications
WebSphere
Convenience Packages
Cost efficient

12. END