> From: Clark Martin <[EMAIL PROTECTED]>Subject: Re: [PCI] 7500 Questions
At 10:06 AM +1000 6/16/04, David Elmo wrote:All the advice from Ron (and others) is sound, just want to add that if you
do get an upgrade processor, try for one with the biggest backside cache you
can (without going over a sensible budget). I would recommend at least 500MB
Ram and a 1MB backside cache. Ram and caches make for just as important
performance boosts as processor clock speed.
And stick to a 2:1 cache if at all possible. That is a cache that runs at half the speed of the CPU -- Clark Martin
In a 7600 I have a Powerlogic G3/4 processor with a 1MB backside, in the Cache Profiler software one can alter the cache ratio from 1:1 to 3:1 with 3:2. 2:1, and 5:2 in between. One can also set the switches on the cpu for different clock speeds. I had 360Mhz at 3:1 (giving a cache speed of 135MHz) for a long time and it was very steady indeed.
But one day, a few months ago, I got all wild and upped the clock speed to 405MHz, keeping the 3:1 backside ratio. All was fine. Recently, I thought, hell, why not up the ratio a notch to 5:2 (going to a backside speed of 162MHz - closer to what I run an excellent XLR8 G3 CPU on my 7300).
But I got more freezes which may be attributable to this cache ratio change (not sure, there are complications). But now you raise this Clark, one of those wild feelings came rushing over me and I have just changed it to 2:1 and will know the effects next few times I start.
Well, anytime you up the clock speed (or any other speed setting) to higher than it's specified value you are risking buggy operations.
You may be better off running it at a slower clock speed and a higher cache ratio (2:1). While you may or may not get a 1:1 cache ratio to work it would be rather iffy. The whole point of the backside cache is to provide a cache in between the CPU speed (L1 cache) and the bus speed (L2 cache).
A G3 gets most of it's performance boost from the backside cache. -- Clark Martin Redwood City, CA, USA Macintosh / Internet Consulting
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