1. BeOS, the Be Operating System
Robert Robinson
CS 550-1

2. What Is BeOS? Coded from scratch 1990: Be, Inc. formed
1996: 1st public release
Ran on Be’s proprietary hardware, BeBox
1997: Be quits the hardware business

3. BeOS History 1998: Release 4, the money-maker
Runs on PowerPC, x86, more
2000: Release 5, “the demise”
“Personal Edition”; 512MB partition limit
2001: Be bought by Palm, Inc.
2001: BeOS R5.1 leaked to public
Today: Haiku (changed from OpenBeOS) and YellowTab

4. BFS, the Be File System Much of structure borrowed from UNIX
Journaling
Reduces data loss
Eliminates need for scandisk or fsck
Rich metadata model
Database-like approach to file retrieval

5. Memory Management Memory Model Implementation at the Microkernel level
Figure 3 – BeOS Architecture
Memory Model
Implementation at the Microkernel level

6. Memory Model Virtual Memory Addresses (mapping dynamic memory)
Shared by threads and processes
Can be locked into RAM
Object-Oriented Design
Full Memory Protection
Symmetric Multi-Processing (SMP)

7. Implementation at the Microkernel Level
BeOS Threads and Objects
Communication between Threads
Message Handling with BLooper
Ports (FIFO message repositories)
Semaphores (data protected locks)
Benaphores (Increased efficiency in data protection)

8. Internal Data Structures
Structures Used in Process Management
Thread creation
Thread execution and control
Thread termination
Structures Used in Memory Management
BLooper (Interface between objects & threads)
Semaphores, Ports, and Images
Structures Used in File Management
Bfile
Bdirectory

9. Threads Multi-threaded Architecture of BeOS Kinds of Threads
Pervasive multi-threading
Teams
Kinds of Threads
Real-time & time-sharing
listener and image threads

10. CPU Scheduler Thread priority numbers: 1-120.
Levels 1-99: assigned to time-sharing threads.
Levels : reserved for real-time threads.
Time-sharing threads are scheduled according to their priority number and a logarithmic scale of 2.
So a thread with a priority number greater by 2 is four times as likely to be chosen to execute.

11. CPU Scheduler (continued)
A new time-sharing thread is given the processor after every time quantum (3 milliseconds in BeOS).
Execution on multiple processors
Time-sharing threads must always yield to real-time threads. This makes BeOS a streamlined OS for media applications requiring real-time performance.

12. Deadlock Problem: Dropping of messages
Solution: Port
Problem: Manipulation of data by another process during execution.
Solution: Semaphores
Problem: Semaphores Slowness
Solution: Benaphores

13. Thread States Running Thread has processor Ready
Thread is waiting for processor
Receiving
Thread is in receive_data() call
Sleeping
Thread is in snooze() call
Suspended
Thread is first created or suspended
Waiting
Thread is waiting to get processor