Oh, the tangled web of processor identification and build selection. Which build for which machine is an oft-asked and necessarily answered question. Here's the scoop.
PowerPC processors come in many wonderful flavors, some Motorola/Freescale, others IBM. Since PowerPC came into being many moons ago, it has undergone many revisions, and has generated a small army of unique CPU cores, each bearing their own special number. These numbers, however, don't quite have the marketing whizbang that Steve the Mighty prefers. The first PowerPC chips in Macs were called, unimaginatively, PowerPC. This was nice at first, but Steve needed something to get the natives riled up at the Macworld keynote, so with the introduction of the PowerPC G3 processor, the tradition of naming the chips based on an entirely arbirary system was born, and thus we have G3, G4 and G5.
The Important Bits
"Thanks for the history lesson, but how does that relate to the build types jerk?"
Well, I'll tell you how. What you may notice about the build classifications on the frontpage is that G3 and Intel are there, but where's the G4? Well, that's where your history lesson came in. 7400 and 7450 are the series identifiers for the different versions of the G4 processor. Over its lifespan, the G4 was improved and modified to a point that GCC (the compiler that we build Firefox with) was able to generate better optimizations for newer G4s that were incompatible with older G4s. Since our effort is not unlike that of an import tuner, we're certainly not going to turn down the possibility of even one microsecond of execution speedup, so we build for both optimization paths of the G4.
"Again, jerk, thanks for the unnecessarily verbose answer, but how do I know which G4 I've got?"
I'll tell you how! You find out what sort of G4 is in your machine! It's actually suprisingly easy. Thanks to the wonders of EveryMac.com, you can find out every arcane, mundane detail about every Apple device since the Apple epoch.
EveryMac.com Apple System Listing
Click through there until you find your baby and look in the column labeled "Processor" and you're in business.
Or, it's been pointed out to me, you could just open a terminal and type "machine". It'll say something clever, like "ppc7450". The rest of this page is more or less meaningless in light of this, but hey, it was fun to write.
"But what's this nonsense with the 7440, 7441, 7447 and 7447a? What do I do about that mess?"
Glad you asked. The 744x series is, counterintuitively, in the same family as the 745x series, but without the capability for L3 cache. If you have a mac with a 7440, 7441, or a 7447/a processor, you want the 7450 build.
"Well, tough guy, I've got a super-mega-ultra-speedy Powerlogix/GigaDesigns/Sonnet Tech/etc upgrade card in my Mac. Everymac has nothing for me, sonny Jim."
A fair point. I'll leave it to you to check either the books that came with your card or the websites for the respective manufacturers:
Once you've found your upgrade card on the website, you'll see which Processor series they used to build them. In almost every case, G4 upgrade card users will want the 7450 builds.
"Well, my good sir, you have been most helpful and genial. Might I inquire as to a "rule of thumb" so to speak, relating, perhaps, the speed of my computer to the build I want?"
Why, certainly. In general, if you have a G4 that's faster than 533Mhz, you almost certainly want the 7450 builds. I've been told that there are some Pismo upgrade cards that used 7410s that don't fit this pattern, but otherwise, it's pretty accurate. Certainly though, if it's a stock G4 from Apple and it's faster than 533, you want the 7450 build.
"Where the devil are the G5 builds?!?!?! OMGROFLCOPTOR"
This has become more commonly asked these days. I used to keep a listing for G5 builds buy a fine gentleman named Drumsticks. His feed stopped updating at some point and so I took it off. It's my understanding you can find his work at InTheMac.com
Well, that about wraps it up. I hope you've enjoyed our time together. Send your processor identification needy friends by and let them know the joy that is understanding the differences between G4 processors!