At 17:09 -0800 01/12/2003, Will Schou wrote: >Finally Powerlogix is going to be selling soon new upgrades for our >machines! >> PowerLogix is also proud to announce the highest performance for older
>> G4, the economical PowerMac G3 800 ZIF features an IBM 750FX running >> at 800MHz with 512K of cache running at a blazing 800MHz. Its great > >The above G3 Zif will likely >fit the Zif carrier cards made by several companies, XLR8 being the >most common but also Powerloix and Newertech made them. However unless >someone comes up with some tricks I don't believe they can run at full >speed in the carrier card looks to me that 700mhz might be the limit so >the cpu daughter card below at the same price is likely the way to go . I think folks are saying that 700 MHz may be the top available because that's as high as one can get with the adjustments available on the carrier card. But there may be some flaws in that reasoning. Some of my reasoning to follow may be flawed as well, as I don't know all the ins and outs, but in one possible universe which may be this one... The 700 MHz limit is being arrived at by looking at the bus multiplier settings available on the ZIF carriers and multiplying it by the top bus speeds available. However, the multiplier settings are just arrived at by taking four pins and either tieing them to ground or voltage in various arrangements. The standard ZIF card has four pins which connect to the ZIF carrier's pins and read that arrangement and interpret it as a bus multiplier (PLL) setting. The 750FX ZIF may interpret those arrangements of the four pins in a different manner than older ZIFs, allowing higher bus multiplier settings (750FX goes up to 20X). There's no reason that "on, off, off, on" must mean 10X for all ZIFs. It could mean 10X for one model of ZIF and 16X for a different model depending on how they're wired. I made that example up. I don't know what the setting is for 10X. So, with clever interpretation of the PLL pins, the 750FX could go up to its maximum bus multiplier settings on existing ZIF Carriers. It depends on what PowerLogix did. Second, ZIF carriers only have four PLL pins. The 750FX has five PLL pins. So no matter how you slice it, existing ZIF carriers are short one PLL pin for the 750FX ZIF card. I don't know what PowerLogix will do about this. Third, some existing ZIF cards ignore the carrier card PLL settings and have their own on-board jumpers or switches for setting the bus multiplier. This is probably the most logical route for Powerlogix to take, given the four pin/five pin incongruency. So, my guess is that the bus multiplier will be set using pins on the ZIF module and that the bus multiplier (PLL) settings on the ZIF carrier card (and the Beige G3 motherboard) will be ignored by the PowerLogix 750FX ZIF. Fourth, the 750FX has the ability to reset it's bus multiplier with software. Some of you may have seen the articles on XLR8yourmac.com about over-clocking the iBook with a software utility. The same would be possible with PowerLogix's 750FX ZIF, assuming that PowerLogix provides such a software utility. All in all, some very exciting upgrades, though I'm not sure how well they compare to the Sonnet G4/800 for us PowerSurge users. True, an 800 MHz G3 should give about the same performance as an 800 MHz G4 for non-Altivec applications, but the caches are very different between the two upgrades. The G4/800 has a 256K L2 cache on the chip which runs at CPU core speed, and a 1 MB L3 cache which runs at 200 MHz. The 750FX (G3/800) has a 512K L2 cache on the chip which runs at the CPU core speed and no L3 cache. So who wins? 256K at 800 MHz helped by 1 MB at 200 MHz vs. 512K at 800 MHz with no helper. The G4/800 isn't that much more expensive depending on what the street prices do. According to the electronics distributer Avnet, pricing on the PPC750FX chip seems to range from $61 to $109 depending on the model and quantity so there may be some cushion in PowerLogix's pricing though not as much as you might think when you factor in all the other stuff that goes into getting a product to market. Still, the chip is the major component in that product. There are no cache chips, so it's just the PPC chip, the tiny (but multi-layered) circuit board, the PGA (pin grid array), and a handful of very inexpensive capacitors and resistors. Finally, the 750FX is supposed to go to 1 GHz and it does support a 20X multiplier, so we could see a (50 MHz X 20) 1 GHz upgrade for our machines without too much effort on PowerLogix's part, now that they have the basic design going. Jeff Walther -- SuperMacs is sponsored by <http://lowendmac.com/> and... 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