Why PBs keep such a low FSB Speed at 166MHz?


macrumors regular
Original poster
Jul 10, 2004
I'm thinking about buying a new pb in couple of days. But I found that the FSB speed on pbs (also on ibooks) is really low at 166MHz, waaaaay too lower than other Wintel notebooks i think.
So why is that? Isn't FSB speed important on pbs for its "special architecture"?

Will pbs with such a low FSB speed will be a lot slower than Wintel notebooks?
I mean, a 15'' new pb with 2gb ram & 128 video ram?


Moderator emeritus
Jul 24, 2002
It's all to do with the CPU. The G4 is designed around (and currently limited to) relatively low FSB speeds. As the G4 does not have the moster pipeline of some x86 chips it can get away with this. The upside is lower heat generation (those fast FSBs suck up a load of juice).

PowerBooks feel plenty fast even with the low FSB.


macrumors 65816
Feb 18, 2003
I am probably wrong (at least partially) here, as I am not very tech-inclined, but the PB's have a 167mhz bus because the g4s do not currently support a higher speed (may actually be the logic board). I cannot say why that is.

As far as what that means performance-wise...as I understand it, the system bus speed determines the rate of which infromation can travel from various components in your computer, such as CPU, Ram, controllers for drives (HD, Optical), and perhaps Graphics cards. In actions that are merely cpu-dependent (like number-crunching/speadsheets) the bus makes little difference, but to activities which require moving data around, like Video or 3D rendering, it can make a difference and become a bottleneck.

Things like caches help alleviate this problem some, giving the cpu a high-speed connection to some portion of memory.

That's about the best I can do, hopefully someone more knowledgeable than me will correct/elaborate on my efforts...
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