[MacDV] Re: iTunes Speed Feedback

[Mark M. Florida]

>    While L3 cache is nice, L2 cache is what's important. When it comes to
> L2 cache, while speed is nice, size is what is important. While Apple says
> that 256kb of L2 cache at full processor speed performs as well as 1 MB cache
> at 1/2 or 1/3 processor speed, for big number crunching this ends up not being
> true; a larger cache. The old 500 MHz CPU most likely had 1 MB of L2 cache.
> The new CPU upgrade probably only has 256kb of L2 cache.

Sneaky, huh?  But they *did* add a Level-3 cache on the PowerMac line --
does that make up for the smaller L2 cache?  I don't know for sure (I'm no
expert on processors), but I'd think it would help.

>    Cycle for cycle, the new generation of G4 processors are not as effcient
> as the original G4 processors. Remember the Motorola G4 processor snafu? G4
> chips could not be clocked faster than 500 MHz. (Well they could, but Motorola
> could not produce enough error-free chips.) In order to get around that issue,
> Motorola redesigned the G4 architeture in order to increase the chip's clock
> speed. (I think it went from a 4 stage pipeline to a 7 stage pipeline.) While
> this enabled faster and faster G4 clock speeds, there was a trade-off in
> processor efficency. Cycle for cycle, your old 500 MHz gets more work done
> than your upgrade.

Actually I think it went from 7 stages to 10.  Anyone remember the big show
in January 2001 when Apple showed the differences between the G4's pipeline
and the P4's?  They showed the G4's 7 stages finishing faster than the P4's
20 stages...  Then they go and up the number of stages to 10?  Actually, the
current crop of high-speed G4s may have even more stages than that...  To
get the higher clock frequencies.

Food for thought.