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  #1  
Old 08-16-2002, 01:44 PM
lwilliam lwilliam is offline
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Default Mac Level 3 Cache - dcornutt?

If anyone else knows, that's cool, too. I just figured the master Mac man here would be very likely to...

Simple question: Is is possible (or practical) to upgrade the Level 3 cache on Macs post-sale?

I'm wondering because the performance tests definitely indicate a LOT of improvement if you have a 2MB L3 cache. I noted that the two new low-end Dual CPU Macs only have a 1MB L3 cache. The two that aren't shipping yet (higher-end) are the only new ones with a 2MB L3 cache.
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  #2  
Old 08-16-2002, 02:54 PM
dcornutt dcornutt is offline
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Default Re: Mac Level 3 Cache - dcornutt?

The largest difference seen so far has really been between having one (an L3) and not having one.

There is some debate as to the marginal difference having over 1 meg of L3 makes.
My guess is...that's the least of the new architecure problems as far as performance...and that adding another meg L3 (if you could)..would not change things much at this point.

The L3 is soldered onto the MB in new macs..and on daughter card of old G4s ...so it's not "upgradeable" in and of itself.

And it does make a good difference between having one and not having one. But, I've seen no hard data about performance increases between a 1 meg L3 and a 2 meg L3..and considering the other limitations of the designs (the front side bus being 1.3gbs shared bandwidth...even though the backside is running at DDR 2.7gbs)...I would guess..it probably would not make much difference at this point between having a 2 meg or 1 meg L3. Thats the least of the worries.

Hope that helps.
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Old 08-16-2002, 04:15 PM
Renie Renie is offline
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Default Re: Mac Level 3 Cache - dcornutt?

That's useful info.

Would you mind saying what you consider the real worries to be and why?

Thank you

Renie
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  #4  
Old 08-17-2002, 12:03 AM
dcornutt dcornutt is offline
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Default Re: Mac Level 3 Cache - dcornutt?

One word. Motorola.

That's apples biggest problem and has been for a while.

having said that...the new machines look nice enough. I believe the 867 and the 1ghz use last years cpu revamped (which cannot take advantage of the DDR speeds..waste of time).

But, well have to wait and see what the new year long developed revision G4 does that produced a whopping 250mhz...speed increase..as far as IF it runs at DDR speeds on the frontside bus.

The new dual gig is about as fast as last years..almost..in the intial bench tests I've seen. For that..it's not a best buy over last years now cheaper dual...since they both have same performance...(at least these initial tests ...mostly cpu related...seem to show)..and they are considerably more expensive. Just would dpend on whether the new goodies are worth it to you or not.

http://www.barefeats.com/pmddr.html

All this leads me to believe that these current macs..are "Yikes" models. Or..I should say..transition models.

The issue with the front side bus...has been around for a while now. Basically..the G4 FSB has a limit of 1.3 gbs datarate thruput. If you look at what the new DDR boards memory controller thruput is...(2.7gbs)...you start to see the problem. One constipated mac.

As I understand it...up unti current...all G4's from moto have this limitation. They cannot communicate at DDR thruput levels.

There is some specualtion as to where the new year long developed 250mhz faster G4 1.2dual chip...can do this or not.

But, the 867 dual and the 1ghz dual are definatley slightly reworked last years chips...that cannot run communicate at DDR speeds on the Front side bus.

But, even though the 867 also has no performance gain from DDR..its now a dual...and 1699...which makes it still a bargain.

We'll see how the new rippin 1.25ghz models do in a few weeks.
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  #5  
Old 08-19-2002, 08:28 AM
Renie Renie is offline
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Default Re: Mac Level 3 Cache - dcornutt?

dcornutt

Thanks for the valuable information and perspective.

Renie
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  #6  
Old 08-19-2002, 11:55 AM
dcornutt dcornutt is offline
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Default Re: Mac Level 3 Cache - dcornutt?

Since the question is coming up more...I posted this more "indepth" discussion concering L3 advantages in any given Mac revision...here.

http://duc.digidesign.com/cgi-bin/ub...;f=24;t=014257
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