Apple MAC G4 Processor Technology & Architecture...

[DannyBoy]

Anyone know anything technical about Apple Mac's CPU Technology?
I mean how similar are they compared to AMD / P4 chips architechture.

Whats so special about the 1mb L3 cache on the G4 etc.

Are they similar? Newer machines use DDR RAM as well i see.

Just discussing the Big & Small Advert for the 12 & 17inch PowerBook's and it suddenly struck me that I know next to nothing about the technology behind their chips.

Any info would be great

Thanks
Dan

 

[kuk]

Here you go!

The Pentium 4 and the G4e: an Architectural Comparison
The Pentium 4 and the G4e: Part II: the Execution Core

Kuk

 

[glugglug]

It's more like a K6/PIII than an Athlon/P4, its behind architecturally other than being 64-bit and having more registers. G4e (newer enhanced version of G4) is more like an Athlon.

My guess is it needs more cache because its had to deal with a slow 133MHz memory bus so long and actually PC processors are LONG overdue for cache size increases. (I had a 1MB L2 cache on my K6-166 system OC to 250.... and today you can't get above 512KB cache except on Xeon systems with absurd prices because they are marketed as "servers").

 

[Remedy]

Link

 

[paralazarguer]

I would recommend that you pick up the March issue of Maximum PC. They put Apple's top cider against an AMD and an Intel PC. It ranged in speed from 40%-60% as fast as the PCs. In short, the mac sucks for speed. No Maximum PC is not biased and the tests were conducted with their sister magazine Mac Addict. Anyway, arstechnica has a couple of great articles about the G4 architecture here , here , and here
Now, that's just about the architecture and doesn't take into account things like the G4s not being able to use DDR memory or several other factors which hold the mac back. Happy reading.

 

[paralazarguer]

argh. All those people beat me to it.

other than being 64-bit and having more registers

IT's not 64 bit. It's a 32 bit processor with SSE extensions just like the athlon/p4.
The L3 cache runs at something like 300Mhz. Since you can buy dual channel DDR333 for the PC, that doesn't impress me AT ALL.

 

[DannyBoy]

Originally posted by: glugglug
It's more like a K6/PIII than an Athlon/P4, its behind architecturally other than being 64-bit and having more registers. G4e (newer enhanced version of G4) is more like an Athlon.

My guess is it needs more cache because its had to deal with a slow 133MHz memory bus so long and actually PC processors are LONG overdue for cache size increases. (I had a 1MB L2 cache on my K6-166 system OC to 250.... and today you can't get above 512KB cache except on Xeon systems with absurd prices because they are marketed as "servers").

Ive always thought that cache sizes were sorta lousy for the top end and high speed processors we have these days.

Does the cache takeup a lot of space in the core or sumthin?

I mean would an increase to 1mb L2 cache on an AXP really be that difficult, would heat be a problem etc?

Thanks for the replies,
more would be kewl

Thanks again
Dan

 

[paralazarguer]

the cache takeup a lot of space in the core or sumthin?

Yes it does. It also ads to the transistor count big time. It means there's a lot more to go wrong in the fab process too leading to lower yields. 1MB of L2 cache would really help in server applications but for gaming it wouldn't do a whole lot. The applications have to grow with the processors. It's a leapfrog effect I think. L2 cache is a very expensive part of the processor.

 

[DannyBoy]

Originally posted by: paralazarguer

the cache takeup a lot of space in the core or sumthin?

Yes it does. It also ads to the transistor count big time. It means there's a lot more to go wrong in the fab process too leading to lower yields. 1MB of L2 cache would really help in server applications but for gaming it wouldn't do a whole lot. The applications have to grow with the processors. It's a leapfrog effect I think. L2 cache is a very expensive part of the processor.

In turn also creating an extremely high amount of heat right?

 

[paralazarguer]

In turn also creating an extremely high amount of heat right?

That's always a factor too. Keep in mind that the G4's cache isn't actually that big. It just has an L3 cache which is nothing more than a stick of DDR soldered to the motherboard...slow DDR at that.

As you may recall the Thunderbird with 256K of L2 cache on die outperformed the Athlon Classic with 512K L2 cache running at half or less speed off die. As you can see, cache speed is more important than size. As clock speed increases, so does cache speed. Be happy with the 512K that we have now. It's actually quite good.

 

[DannyBoy]

Sounds good