1. Mac OS X Panther Operating System
Tomomi Kotera
CS 550 Section 3
Fall 2003

2. Presentation Overview
Overview of Mac OS X
System Architecture
Key technologies
CPU scheduling
Symmetric Multiprocessing
Memory Management
Conclusion

3. Overview of Mac OS X
UNIX-based Operating System with the intuitive user interface called Aqua
“Classic” Mac OS vs. Newer Mac OS
Four major successes of Mac OS X
Preemptive Multitasking
Symmetric Multiprocessing
Memory Protection
Virtual Memory

4. System Architecture Four layers of system software
Application Environments
Application Services
Core Services
Kernel Environments

5. Preemptive Multiprocessing
Cooperative multitasking (Classic Mac OS) vs. Preemptive Multiprocessing (Mac OS X)
Preemptive Multiprocessing
Multilevel Feedback Queue Scheduling Algorithm
Round Robin Scheduling Algorithm

6. Preemptive Multiprocessing (cont.)
Multilevel Feedback Queue Scheduling Algorithm
128 priority levels are divided into four bands
Normal (0-51)
System High Priority (52-79)
Kernel Mode Only (80-95)
Real-Time Threads (96-127)
Real-Time Threads are treated differently
Avoid Starvation
Threads migrate within a given band

7. Symmetric Multiprocessing
Dual processor capabilities
Share Memory and I/O bus
Kernel can execute on any processor

8. Memory Protection Crush Resistant
Processes are isolated in own memory spaces
Cannot interfere one another
If one applications crashes, the system, and other applications are unaffected - no restarts

9. Virtual Memory Classic Mac OS uses Segmentation
Mac OS X adopts Demand Paging
Large, sparse virtual address spaces
Mapping a page reference to a physical address
pager
application
Address space
Function call
Page
fault
resume

10. Virtual Memory (cont.) VM Object (Virtual Memory Object)
Object-oriented nature of Mach
Contiguous repository for data indexed by byte
All data in an address space is provided through VM objects
Track and manage the resident and nonresident pages
Memory Sharing
Inheritance (shared, copy, none)
Copy-on-Write

11. Virtual Memory (cont.) Content of a VM object
Field
Description
Resident pages
List of resident pages in physical memory
Size
The size of the region, in bytes
Pager
The pager responsible for tracking and handling the pages of this region in backing store
Shadow
Used for copy-on-write optimizations
Copy
Attributes
Flags indicating the state of various implementation details

12. Virtual Memory (cont.)
Second-chance first in, first out (FIFO) Algorithm
Three lists of physical memory pages
List
Description
Active list
pages that are currently mapped into memory and have been recently accessed
Inactive list
pages that are currently resident in physical memory
Free list
pages of physical memory that are not associated with any address space of the page table

13. Virtual Memory (cont.) Continuously check the free list
When the number of pages in the free list dips below this threshold, remove pages from the inactive list to place them on the free list
Always maintains a few pages on the inactive list
Once the free list size exceeds the target threshold, the pager rests
FIFO-like page replacement
The inactive list serves as a second chance

14. Conclusion Technical Success of Mac OS X
Marriage of stability, reliability and security of UNIX, with the ease of use of the Macintosh GUI
Benefits from UNIX features
Preemptive Scheduling
Symmetric Multiprocessing
Memory Management
Target both home users and IT professionals