Much has been made of the recent purchase by Apple of semiconductor design company P.A. Semi. That move has puzzled many Apple observers and many theories have been spun to explain it.

P.A Semi is a fabless semiconductor company, meaning that they design chips but don’t manufacture them. They have recently been focused on developing the PWRficient family of processors. The processors are Power PC compatible, 64-bit, multicore, very fast, but very low-power. When you consider that Apple previously used Power PC processors in the Macintosh and switched to Intel largely because they needed faster, low power chips, then one potential explanation is obvious.

Most of the theories regarding the acquisition seems to concern one of these five ideas:

1. Apple is attempting to extract price concessions from Intel by threatening to use P.A. Semi chips.
2. Apple wants some item or items of intellectual property developed by P.A. Semi.
3. Apple wants the 150 engineers employed by P.A. Semi.
4. Apple plans to use P.A. Semi chips in a future iPhone or iPod.
5. Apple plans to switch back to Power PC chips in a future Macintosh.

According to the Wall Street Journal Business Technology Blog, Steve Jobs himself suggested (but did not actually confirm) that numbers three and four are the real reasons.

My personal favorite is number five, although I think that such a move is extremely unlikely. Switching to Intel processors was certainly a good business move that helped Apple lower costs and increase sales. But from a purist’s point of view, the move to Intel robbed Apple of some of its charm.

After they made the switch, Steve Jobs confirmed that Apple had been maintaining an Intel version of OS X for two years. I think that statement has led people to underestimate the difficulty of porting an operating system to another processor. Even if the operating system is designed for portability, it is not a trivial undertaking, certainly not something done on the off chance that it might prove useful later. The Intel port was developed not just with some vague idea of portability, but because Steve Jobs had been considering a strategic move to Intel for some time.

The Power PC is a different story, because Apple still maintains the Power PC version of OS X for older Macintoshes. A switch back to the Power PC would be possible at any time, although I don’t see what Apple could expect to gain in the short term. But it might make more sense as part of a long-term plan, especially if Steve Jobs sees a future problem with Macintosh cloning. Some people have been predicting the demise of the Power PC version of OS X in the near future. If P.A. Semi is actually part of a long term plan for the Macintosh, then maybe the Power PC version of OS X will continue to be developed, just to keep all options open.