Mac OS X operating system

Mac OS Classic
| Mac System Software 1 | Mac System Software 2 | Mac System Software 3 | Mac System Software 4 | Mac System Software 5 |
| Mac System Software 6 | Mac OS 7 | Mac OS 8 | Mac OS 9 |

>> Mac OS X <<
| Mac OS X 10.1 Puma | Mac OS X 10.2 Jaguar | Mac OS X 10.3 Panther | Mac OS X 10.4 Tiger | Mac OS X 10.5 Leopard |
| Mac OS X 10.6 Snow Leopard |

Related:
| Motarola PowerPC CPU | Intel x86 CPU CPU | Intel x86 64-bit CPU |

Mac OS X 10.4 added support for Intel x86 CPUs. PowerPC CPU support was dropped after Mac OS X 10.5

Since only the 10.0 to 10.1 was free upgrade (the others you have to buy), there's separate tags for each "major" version of OS X.

OS X is written in Objective-C, the Kernel is pure C language (the kernel is based on BSD and the Mach kernel which are both C). Some subsystems are written in C++ but great care is taken to not expose the C++ code to the C and Objective-C compilers that the core of OS X so OS X is not written C++.