I have a general question regarding the pros & cons of using a ZIF CPU with
a carrier card (such as Daystar) versus a specialized upgrade such as a Sonnet
G4. I can see how the carrier is more versatile, allowing you to use any G3
or G4 ZIF CPU. But aren't you restricted by the bus speed? I would think
this would limit your processor speed to 450 - 500 mhz without
over-clocking. Sonnet can supposedly hit 700 - 800 mhz with their G4
Crescendo PCI upgrades. Do these really perform at 700 - 800 mhz levels?
How do they get around the bus speed limitations? Prices for these two
options seem to be comparable. Page Computers has the G4 700 upgrade
for $237, which seems in line with the Daystar carrier & processor, but if the
Sonnet actually runs at 700 mhz, wouldn't that be the preferred choice?
Thanks in advance.
They both have approximately the same bus speed limits. The higher speeds are possible because newer CPUs support higher multipliers.
For example, originally, the best multipliers available were 8X on a G3 and 9X on a G4. So with a 50 MHz bus speed, the best one could do was 400 MHz on a G3 and 450 MHz on the G4. Then IBM produced a G3 with a 10X multiplier and the G3 popped up to 500 MHz.
Additionally, if one was able to overclock the bus speed a bit, say to 60 MHz, then those top speeds for 8X, 9X and 10X changed to 480 MHz, 540 MHz and 600 MHz respectively. But that was only true in practice if the 400 MHz CPU would tolerate running at 480 MHz, the 450 would tolerate 540 and the 500 would tolerate 600.
The new Sonnet upgrades run at a bus speed of 50 MHz and use a bus multiplier of 14X and 16X for the 700 and 800 MHz G4s, IIRC. The Sonnet card is a marvel of engineering in some ways solving some interesting compatibility problems (which don't apply to our Umax machines) but causing others. For example, it simply won't work with an Atto UL2D SCSI card installed. For those of us who picked these (the SCSI card) up cheap a year or so ago, that's irritating. I think that they also have problems with OSX but I have not been following that discussion carefully, so I'll leave it to someone better versed in X to comment. But if true, it's an issue because the primary advantage of the G4 over the G3 is in X where many of the OS routines make use of Altivec.
The ZIF upgrades use similar bus speed and multiplier settings. PowerLogix has a newish card based on the latest IBM G3 chip which supports up to 20X multipliers (in theory). I may be a little out of date, but they were selling an 800 MHz version which could run with a 50 MHz bus speed and a 16X multiplier. IBM was planning to get that chip up to 1 GHz at least.
So, my personal opinion is that I would avoid the Sonnet product because of the compatibility issues unless they have a product that just perfectly fits your needs.
Somebody (Will, I think) reported that there were reliability problems with the PowerLogix processor cards. So you might want to look at the offerings from Daystar/XLR8. Gary Dailey seems like a really good guy.
Jeff Walther
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