DDR - DDR2 Differences?

Caporegime
Joined
1 Nov 2003
Posts
35,691
Location
Lisbon, Portugal
Hey guys,

currently getting back into todays hardware,

now DDR2 is it worth it?

just looking at a kit on our very one OcUk's website

G.Skill 2GB DDR2 NR PC2-6400 (2x1GB) CAS5 Dual Channel Kit (F2-6400PHU2-2GBNR) (MY-014-GS)
Price: £114.95 (£135.07 Including VAT at 17.5%)

Now imo thats cheap for PC6400 RAM especially 2gb of it, but its CAS5 surely thats a bad thing? someone please explain :) surely it should be around CAS3 or CAS2.5??
 
Caporegime
Joined
8 Jan 2004
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31,994
Location
Rutland
As said, the slack timings are overcome by running the RAM at higher frequencies, meaning latency is actually less than DDR.

DDR2 is relatively cheap to produce and is scaling well too.
 
Caporegime
Joined
8 Jan 2004
Posts
31,994
Location
Rutland
Cyber-Mav said:
what you want is ram that does 1000mhz at 1-1-1-5 timings. then and only then will there be some serious speed up's

Well A64 has never needed much in the way of memory bandwidth, so its not seeing gains with DDR2, admittedly your uber-RAM would be nice, but we need to see some new A64 cores that can put all this bandwidth to use :D
 
Caporegime
Joined
18 Oct 2002
Posts
33,188
a easy way to think about it is like a harddrive, seek time versus continuous reads. if you need to access lots of different data then you have to keep telling the memory where to read, while the memory basically have no seek time the comparison here is the cpu having to keep asking the cpu being the seek time, with a cas latency of 2 you have to wait 2 clocks out of the 400 before it can go fetch it. where as on the ddr2 you'd have to wait say 4 clocks, but its running at 800mhz so its actually waiting the same amount of time, the latency in seconds is the same, just the clock latency is different.

however, just like with hard drives if you know where all the data you want is you can tell the memory to send it a bigger stack of data with less seeking time, as with a continuous read on a hard drive being much faster than multiple smaller reads. with ddr2 the higher speed causes higher bandwidth, but due to the other latencys being higher its not simply double the bandwidth, it has to wait a certain amount of clocks here and there, but its no doubt faster.

am2 brings with it between say 1-10% difference in most areas, probo averaged out at maybe 3%. this is the same kind of difference a system will see if you run cas 2,2,2,5 ddr400 over cas 2.5,3,3,8 memory which a lot of people would upgrade to, but ddr2 isn't something people jump to upgrade. as for speed, am2 is faster, within a couple days of the big benchmark guys getting their Es or retail am2 systems they all had new higher scores to post, maybe not hugely higher but they are still higher.

people seem to constantly say one platform over another benefits or doesn't benefit as much from low latency memory. 2 clocks is 2 clocks on any platform, every platform has to access memory constantly, upgrading any system with slightly lower latency memory gives very similar performance increase on any system. faster is always better, there are differences, with better branch prediction cache can hopefull stay ahead of the cpu thereby bypassing a lot of the latency of accessing memory if it can preload memory before cpu needs it. it doesn't work all the time, the cache still needs to access the memory. conroe's cache, branch prediction is much improved, but its pipeline is a little longer than ath 64's so when it needs to flush it, it would take an extra few clocks to refill it than an ath 64. all that tends to even out though.
 
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