by , 3:15 PM EDT, October 1st, 2007

Whenever Apple comes out with a major new release of its OS, some Macintosh hardware gets left behind. While Leopard includes support for PowerPC Macs, it's worth looking at Apple's history to see if Mac OS X 10.6 will abandon the entire PowerPC line, according to Daniel Dilger at Roughly Drafted.

"Previous versions of Apple�s OS have drawn the line for officially supported Macs based on practical considerations, rather than just being arbitrary or artificial. Here's what the past suggests for Mac OS X Leopard and the version that comes after it," Mr. Dilger wrote.

It turns out that there are some fairly frequently used metrics for deciding whether a new OS version needs to leave a line of hardware behind. By looking at how Apple has done this going all the way back to System 7 in 1996, it's possible to make a good prediction about what Mac OS X 10.6 will support.

While Apple has a tendency to make radical changes in hardware, such as the Motorola 680x0 transition to PowerPC, then PowerPC to Intel, the pace of change has still afforded a rather generous position by Apple in how far back they go.

For example, "The release of Mac OS X Panther 10.3 in 2003 extended support back to Macs with G3 processors and built-in support for USB. This wasn't due to an actual requirement for USB, but rather a shorthand way to describe a cutoff for the support of the significantly different architecture of "Old World" Macs designed prior to the iMac, as all New World Macs also provided support for USB. Panther retained a roughly five year support window for existing Mac models," Mr. Dilger noted.

Another major factor to consider is the aggregate of how many Macs lie within, say, a five year window in the past. For example, the majority of the installed base of Macs today, about 22 million, is still PowerPC. These customers will be buying software well into 2010. In addition, the architecture of recent Macs, even through the PPC to Intel transition, hasn't changed that much since 2003.

There are additional technical considerations, thanks to the way Apple has set up its 32- and 64-bit architectures, something Microsoft has had trouble with. The bottom line was easy to arrive at. "Worrying about 10.6 or even 10.7 being Intel-only shouldn't be among anyone's greatest concerns," Mr. Dilger concluded.