1. Scott Ferguson Section 1
Mac OS X
Scott Ferguson
Section 1

2. Introduction Background information on OS X
Description of the OS X Architecture
Mach Kernel
Multithread Scheduling
Memory Management
Multiprocessing
BSD-UNIX Components
Networking
File Systems
Unix Security
I/O Kit

3. OS X Overview 1997 Apple acquired NeXT, Inc. and their NextStep OS
Apple wanted to create an operating system with the power and efficiency of UNIX and the ease of use of the current Mac OS.
Apple release first version of OS X in 2001

4. OS X Overview In what environment is this OS designed to work?
Designed to be used only with Apple computers
Supports single and multiprocessor systems
Did this OS advance the state of the art?
Replaced “classic” Mac OS
Succeeded in making UNIX system easy to use

5. OS X Overview Is it commercially successful?
Mac OS holds about 3% of the current market share
What was done right/wrong?
High Quality Product
Frequent Updates

6. OS X Architecture
The kernel is the core that provides basic services for the other parts of the operating system.
The Mac OS X kernel environment includes the Mach kernel, BSD-UNIX, the I/O Kit, file systems, and networking components.

7. Kernel Environment

8. Mach
Mach manages processor resources such as CPU usage, handles scheduling, provides memory protection, and provides a messaging-centered infrastructure to the rest of the operating-system layers.
The Mach component provides:
Inter-process communication (IPC)
remote procedure calls (RPC)
scheduler support for symmetric multiprocessing (SMP)
support for real-time services
virtual memory support

9. Mach Scheduling
Mach scheduling is based on a system of run queues at various priorities that are handled in different ways. The priority levels are divided into four bands according to their characteristics
Priority Band
Characteristics
Normal
normal application thread priorities
System high priority
threads whose priority has been raised above normal threads
Kernel mode only
reserved for threads created inside the kernel that need to run at a higher priority than all user space threads
Real-time threads
threads whose priority is based on getting a defined fraction of total clock cycles, regardless of other activity

10. Memory Management Dynamically assigns memory to applications
Includes a fully-integrated virtual memory system that you cannot turn off
OS X does not use a pre-allocated swap partition for virtual memory. Instead, it uses all of the available space on the machine’s boot partition
Memory assigned to applications are protected from other memory segments, preventing conflicts and crashes

11. Multiprocessing OS X implements Multiprocessing by using SMP
Handles multiprocessor-ready applications by splitting the application into multiple independent threads, which the underlying operating system then schedules to run on multiple processors.
Automatically assigns threads/tasks to available processors in a way meant to maximize overall execution speed.
Uses “critical regions” to restrict access to a given shared memory range to one thread/task at a time.
Also, OS X provides semaphores for use as a synchronization mechanism among cooperating threads/tasks

12. BSD
Above the Mach layer, the BSD layer provides advanced networking, security, and compatibility features
The BSD component provides
File systems
networking services
UNIX security model (user IDs and Permissions)
BSD Application Program Interfaces (APIs)
The system framework for exporting APIs to the application layers
Multi-user Access

13. I/O Kit
The I/O Kit provides a framework for simplified driver development, that supports many categories of devices.
The I/O Kit component provides
dynamic device management
dynamic (“on-demand”) loading of drivers
power management for desktop systems as well as portables
multiprocessor capabilities

14. Conclusions
Mac OS X provides a powerful UNIX-based operating system with an easy to use interface
The Kernel environment, which includes the Mach Kernel, the BSD-UNIX components, and the I/O kit, provide all of the needed services to the operating system (CPU, Memory Management, VM, Networking, Security)
The real success in OS X is that its Aqua GUI has managed to “hide” the UNIX from the user

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