XPostFacto
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XPostFacto is an open source utility that enables the installation of PowerPC versions of Mac OS X up to 10.4 on some PowerPC-based Apple Macintosh systems that are not officially supported for them by Apple.
XPostFacto - often referred to as "XPF" - runs under Mac OS 9 and allows an unmodified Mac OS X installation disk to be launched on machines which cannot boot Mac OS X unaided. This allows Mac OS X to be installed on certain Mac models which could otherwise only run System 7, Mac OS 8 or Mac OS 9, albeit sometimes with incomplete functionality.
It also allows more recent versions of Mac OS X to be installed on older G3 Macs which can only run older versions - for example, it allows Mac OS X v10.3 and Mac OS X v10.4 to run successfully on Beige G3s. It can even facilitate otherwise-awkward installations on supported machines; for instance, it allows Mac OS X v10.4, which shipped on DVD media, to be installed onto a Blue and White G3 which has only an external, non-bootable DVD drive.
For example, it can install Mac OS X v10.2 on a Power Macintosh 8600, Mac OS X v10.3 on a beige PowerMac G3, and even Mac OS X v10.4 on the earliest iMac G3s.
The name is a pun on ex post facto, a Latin phrase meaning "after the fact", commonly used in legal matters to refer to retroactive actions applying a later state of affairs (such as legislation) to earlier situations. In this context, it refers to the installation of software which did not exist yet at the time the hardware was manufactured: it retroactively "applies" Mac OS X to pre-existing hardware.
This software engineering feat by developer Ryan Rempel is made possible by the publication of the source code for Darwin, the open-source foundation of Mac OS X.
XPF's functionality is achieved via three different routes. The program provides a replacement boot loader for Macs with OldWorld firmware, provides a set of kernel modules to allow the Mac OS X kernel to support various pieces of system hardware which are unsupported in the retail release, and includes a mechanism to transparently boot the kernel off a supported medium - termed a "helper drive", such as the internal hard disk - even when installing Mac OS X to or from a non-bootable volume, such as a USB optical drive or a hard disk which is unsupported by the kernel or system firmware.
XPF does not support all models of Power Macintosh. Only certain PCI-based models with Open Firmware will work. It does not support NuBus-based PowerMacs.
Once Mac OS X has been installed, XPF also runs under that operating system. On unsupported machines, XPF should be used instead of Apple's "Startup Disk" control panel or system preference pane to select whether the Mac should boot into Mac OS X or an older version.
Although experimental versions of XPF were available before the release of Mac OS X v10.2, v10.3 and v10.4, no version was available at the time of the release of v10.5 and XPF 4 does not support Mac OS X v10.5.
