The Development Of OS X

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Introduction

Decades of operating system development and a collection of systems and features from many other systems combined with many unique ideas and implementations resulted in the development of Apple, Inc.'s OS X family. It is necessary to examine the older systems of OS X as well the progress of the system to understand the different technologies and how they interact. To secure and troubleshoot problems it is of great importance to understand the how and often the why of OS X technology.
The open source core of the system is an operating system called Darwin. Darwin is a variant of BSD Unix running on the Mach 3 microkernel from Carnegie Mellon University and the Open Software Foundation (Singh, 2007). On top of Darwin, Apple uses both open source and proprietary code and builds a complex and sophisticated operating system that maintains the look and feel of classic Macintosh computers with little or no compatibility to historical (1980s) Macintosh underlying technology. In fact OS X is more compatible with its sibling UNIX systems and with Microsoft Windows than with past Apple computers. OS X is a UNIX 03 system as certified by the Open Group and listed on their register (The Open Group, 2014). OS X moves forward rapidly and sometime controversially, embracing new technologies, devices, and interfaces. For example:- Animations and graphics used in the system became more sophisticated, then requirements started to include hardware accelerated graphics capabilities. OS X has also switched architectures once in its brief history, from PowerPC to Intel, which was followed by moving to requiring 64-bit processors. At the same time iOS shares a lot of technology and code with OS X and runs on still an...

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The transition from ipfw to pf is nearly complete. pf has already been in use as early as 10.7 Lion. The manual page for ipfw is clearly marked as deprecated, instead recommending pfctl, and in 10.9 Mavericks only the deprecation warning remains. Upstream FreeBSD and OpenBSD resources document both systems well, but OS X has some unique configuration and few changes from upstream.
The upstream pf documentation from the OpenBSD project is extensive, detailed, and an excellent resource for the utilities and configuration language of the current version. Unfortunately, OS X uses an older version and there are some mismatches between OS X pf and the current version of pf on OpenBSD and other systems. A detailed explanation of the differences is available in an upgrade note for OpenBSD 4.7 where the change occurred upstream (OpenBSD, 2009).

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