Well, I'm sure performance would be better with DDR400.
No argument there, but the point is that the improvement might not be worth the increase in cost and/or there might be better alternatives. If they could build a dual channel DDR333 system for only slightly more than a DDR400 system, for example, then the former would be an obvious choice. Alternatively the choice might be between DDR333+L3 cache and just DDR400. There are many possibilities and lots of factors going into the design process. Saturating the available FSB bandwidth is not a key requirement.
I wonder if Apple will go the route of putting an embedded L3 cache in the companion chip. 4 or 8MB would go along way to maximizing performance while they use more common and less expensive memory technology like single channel DDR333.
I wonder if Apple will go the route of putting an embedded L3 cache in the companion chip. 4 or 8MB would go along way to maximizing performance while they use more common and less expensive memory technology like single channel DDR333.
With embedded, do you mean ram built into the companion chip itself?
The issue with dual-channel DDR is that yeah, the memory bandwidth holds up for writes ... but not always so for reads. It's really interesting how Rambus RAM is going to break 1333 MHz soon though Intel has all but dropped it, SiS has picked it up. Still has the latency issues though.
With embedded, do you mean ram built into the companion chip itself?
Yep, SRAM specifically. Getting 450MHz SRAM (DDR to 900MHz) is not expensive and building it into the cost of the companion chip would be a way to save on overall costs, especially by going with a less exotic RAM alternative like single channel DDR.
Yep, SRAM specifically. Getting 450MHz SRAM (DDR to 900MHz) is not expensive and building it into the cost of the companion chip would be a way to save on overall costs, especially by going with a less exotic RAM alternative like single channel DDR.
Ok. The next question is: what kind of performance improvement would this produce compared to say DDR333 (w/o L3) that is the most likely candidate for the system ram. (A lot, but is it enough for Apple to actually make it)
A more cost-effective option would be to build a L3 cache controller into the companion chip, and use a sram card of some sort (or solder it to the motherboard). If that were the case, Apple could use the same companion chip in several different macs with different L3 cache sizes.
Yep, SRAM specifically. Getting 450MHz SRAM (DDR to 900MHz) is not expensive and building it into the cost of the companion chip would be a way to save on overall costs, especially by going with a less exotic RAM alternative like single channel DDR.
I like the idea. But the 512KB L2 takes already 1/6 - 1/5 of the die of the 970. So you're talking about a companion chip with a die size 50% langer than a 970 (3 times as big with 8MB cache).
Wait? Wasn't the whole point of giving the PPC970 a fast bus, so it wouldn't need an expensive L3 cache?
PC3200 RAM is not as expensive as you guys are claiming. Look, you can buy 512MB it right now from Crucial for under $100. 512MB of PC2700 RAM costs about $20 less.
Are you telling me Apple is going to worry about saving $20-40 on some part in a professional, high-end, top of the line machine? Please. Going with PC2700 and adding an L3 cache is going add more to the cost.
Comments
Originally posted by Programmer
There is no requirement that the bus be saturated. Up until recently it was normal for the bus to not be the limiting factor.
Well, I'm sure performance would be better with DDR400.
Originally posted by Kecksy
Well, I'm sure performance would be better with DDR400.
No argument there, but the point is that the improvement might not be worth the increase in cost and/or there might be better alternatives. If they could build a dual channel DDR333 system for only slightly more than a DDR400 system, for example, then the former would be an obvious choice. Alternatively the choice might be between DDR333+L3 cache and just DDR400. There are many possibilities and lots of factors going into the design process. Saturating the available FSB bandwidth is not a key requirement.
Originally posted by Outsider
I wonder if Apple will go the route of putting an embedded L3 cache in the companion chip. 4 or 8MB would go along way to maximizing performance while they use more common and less expensive memory technology like single channel DDR333.
With embedded, do you mean ram built into the companion chip itself?
Originally posted by NETROMac
With embedded, do you mean ram built into the companion chip itself?
Yep, SRAM specifically. Getting 450MHz SRAM (DDR to 900MHz) is not expensive and building it into the cost of the companion chip would be a way to save on overall costs, especially by going with a less exotic RAM alternative like single channel DDR.
Originally posted by Outsider
Yep, SRAM specifically. Getting 450MHz SRAM (DDR to 900MHz) is not expensive and building it into the cost of the companion chip would be a way to save on overall costs, especially by going with a less exotic RAM alternative like single channel DDR.
Ok. The next question is: what kind of performance improvement would this produce compared to say DDR333 (w/o L3) that is the most likely candidate for the system ram. (A lot, but is it enough for Apple to actually make it)
A more cost-effective option would be to build a L3 cache controller into the companion chip, and use a sram card of some sort (or solder it to the motherboard). If that were the case, Apple could use the same companion chip in several different macs with different L3 cache sizes.
Originally posted by Outsider
Yep, SRAM specifically. Getting 450MHz SRAM (DDR to 900MHz) is not expensive and building it into the cost of the companion chip would be a way to save on overall costs, especially by going with a less exotic RAM alternative like single channel DDR.
I like the idea. But the 512KB L2 takes already 1/6 - 1/5 of the die of the 970. So you're talking about a companion chip with a die size 50% langer than a 970 (3 times as big with 8MB cache).
I don't think this to be inexpensive.
PC3200 RAM is not as expensive as you guys are claiming. Look, you can buy 512MB it right now from Crucial for under $100. 512MB of PC2700 RAM costs about $20 less.
Are you telling me Apple is going to worry about saving $20-40 on some part in a professional, high-end, top of the line machine? Please. Going with PC2700 and adding an L3 cache is going add more to the cost.