Architosh Staff ([email protected])

28 Mar 2001

Mac OS X: Core Technologies Overview -2

Continued from:

In this series will be be detailing Mac OS X from a "system overview" perspective. Many readers have never had the chance to fully delve into Mac OS X's technical background beyond the material posted at Apple.com.

A Darwin Story

Apple has now made the claim that they are the world's largest Unix vendor based on their installed user-base. Just like that. Overnight...it seems...the Mac has suddenly become a UNIX platform. And Mac OS X has descended from a long lineage of distinguished UNIX operating systems and technologies.

Even further, Mac OS X will shortly become the dominate UNIX operating system, even surpassing Linux (especially any one variant of it) on the desktop...and likely, the workstation in due time. And all of this is great news for Macintosh users whether they understand the implications of it now or ever. All Mac users in the future on OS X and beyond will benefit from the evolution and story of Darwin, the UNIX core of Apple's newest operating system.

Why Darwin Makes OS X A 'Modern OS'

Darwin is the foundation of Mac OS X. It is also an 'open-source' Unix operating system with a similar open-source license, like Linux. What Darwin does is "integrate" a number of advanced Unix technologies, including Mach 3.0 and operating-system services based on version 4.4BSD Unix (Berkeley Software Distribution Unix)

The Required Elements of a Fully Modern OS Are:

• Full Protected Memory

(Mach 3.0 makes it virtually impossible for a single application gone awry to hurt the rest of the system by walling off each application into its own memory (address) space.) This walling off includes system processes, which is why theoretically you could crash dozens of apps a day and never have to reboot Mac OS X.

• Pre-emptive Multitasking

(Mach performs as a time manager over the processor(s), watching over each applications' "processes" with the CPU and scheduling all processes in a manner which ensures maximum performance across the whole system. Mac OS 9 and earlier had what was called Co-operative Multitasking, wherein apps had to cooperatively police their own time with the CPU. In the old Mac some apps would hog the whole processor.)

• Advanced Virtual Memory

(Mach is different than other virtual memory systems in that it "maintains address maps that control the translation of a task's virtual addresses into physical memory". Only portions of a task's code are resident in physical memory at any one time.)

• Multi-Processor Support

(Mac OS X supports multiple G4 and future G5 processors, such as the currently shipping dual processor G4 Power Mac systems. Multi-processor support is state-of-the-art in Mac OS X as it has been developed from the ground-up to take advantage of multiple processors from the kernel level up. Mac OS X can support up to four (4) processors compared to Windows 2000 Professional which supports up to two (2).

• Multi-Threading Support

(To really take advantage of multiple processors Mac OS X supports various threading models for developers to thread their applications for OS X. Conceptually what threading does is take application code and modularize it into strands that can run preemptively or even better concurrently (on multiple processors). This speeds up applications considerably, enabling high-end rendering applications, for example, to cut rendering times in almost half.) We will have more on Threading later.

• Real-time Support

(This not often discussed aspect of OS X essentially guarantees access to processor resources for time-sensitive media applications, like 3D flybys rendered in real-time, real-time video-effects, etc. etc.)

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