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

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

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

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

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

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

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

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

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

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

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

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

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

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