FSB and caches???


macrumors member
Original poster
Sep 4, 2004
Hi All!

I have a couple of questions.

What is FSB? What does it mean? Is it the same as system bus? If so, what is the system bus?

And how does a PB (with FSB of 167Mhz and 512K on-chip level 2 cache) compare with some of the PC laptops (e.g. dells, sonys, etc.) that have much higher FSBs and level 2 and 3 caches.

What do level 2 and level 3 caches mean?

Will the PB's FSB and amount of cache affect the performance of the machhine in comparison to those PCs (I want to be able to do DV editing on the move).

Sorry if I appear ignorant but I really have no clue about these things and would appreciate some advice from some of you guys.

Many thanks,



May 26, 2004
Randy's House
I only know that FSB stands for front side bus, which is the conduit between the processor and the rest of the machine. Tha higher the speed, that faster it can move data out--but keep in mind the x86 and Mac architecture are different, so FSB speeds may not be comparable.

Cache is actual memory on the chip itself (I think).

Have a look at the architecture sections on Apple's site, that may help.


macrumors 603
Jun 25, 2002
LaLaLand, CA
A FSB is a Front Side Bus. Basically how the Processor, or CPU (Central Processing Unit), talks to the rest of the system. Like with RAM. The PowerBook has a G4 with a 167MHz FSB, with some support for 333MHz DDR RAM (DDR = Double Data Rate, so 333 is actually 167 rising and falling). AMD CPUs used to be DDR, like a 400MHz FSB would have been 200 rising and falling, just like 400MHz DDR RAM. Intel uses a system where the FSB is Quad-pumped (travels along 4 paths), so a 533MHz system bus is actually 133 x 4. It gets more technical than that, but that's the gist. Also, remember that just because something has a higher clock speed, it doesn't mean it's faster. There are other factors. Look up Megahertz Myth.

L1 and 2 (Level 1 & 2) Cache are small amounts of memory, usually on the chip nowadays, that works like a small amount of RAM that talks directly to the CPU, usually at full speed, or around half, speed of the CPU. The G4 has 512k. It can speed things up. Think of it like a line. CPU-Cache-FSB-RAM-Hard Drive. Like I said, that's just the gist. I'm sure some more technical people can help you better, and a quick Google search (or the Search button here, I'm sure there are lots of threads about it) will offer some pretty good explanations.

Can't really compare G4s to P4s, or even Athlons. For some things, it will be faster on a Mac. For others, faster on a PC. P4 (or P4M, for Mobile) vs. Athlon is a better comparison, because they run the same Operating System, but even that can be hazy because there is no clear winner. Some things one is better, somethings the other. But if you want to do DV, especially on a Laptop, I'd go with the Mac. It may not be as fast as a full size PC Laptop, but it is lighter than most and the software is infinitely better on the Mac IMO. Intel's Centrinos are fast, and some have good batter life, but Windows isn't exactly great for video (again, IMO).

Best thing to do is play with a P'Book and see if it's fast enough for you. Compare it to a PC, hardware and software, and see which one you prefer. I'd love to tell you just to get a Mac, but that's just a personal preference. I don't edit movies on my PC at all. FCP, FCE, and iMovie have no comparison on the Wintel side, IMHO.


Dec 30, 2002
the 167MHz FSB is probably the only thing I have against the G4. The chips speed is fast enough, and it being the 32-bit doesn't really matter, but that bus is still a big bottleneck that I wish they'd fix.
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