DDR vs DDR2 Options

[enwar3]

ok, so what is better, ddr or ddr2?

ive found that ddr will come at lower frequencies, but also lower latencies (CAS2), while the ddr2 runs at best CAS3 and mostly CAS4.

why is this? will the faster frequencies for ddr2 make up for a higher latency?

[JBbons]

Got this from AMDEdge:

As part of our continuing effort to keep you informed of the latest trends in computing technology, this brief write-up on memory gives an overview of DDR2, a method for increasing a system's memory performance. We hope you find the information, well? memorable. Please note: AMDEdge articles and guides are intended for technically advanced users. Please review important cautionary information at the end of this article.


What is DDR2?

?Double Data Rate, Two? or simply, DDR2, is an extension of a system's standard DDR memory. Like DDR, DDR2 transfers data on both edges of the system clock, which allows the bandwidth of the memory to equal twice that of Single Data Rate memory, or SDRAM. DDR2's architecture is intended to increase efficiency and performance over its predecessor, DDR.

What are some of the major differences between DDR and DDR2?

One of the main differences between DDR and DDR2 memory is the required voltage at which the memory runs. DDR's standard voltage setting is 2.5 V, while DDR2's voltage setting is 1.8 V. Although it may not be a phenomenal difference, the lower voltage specification allows more space for operation at higher frequencies.

A second difference between DDR and DDR2 memory is DDR2's 4-bit data pre-fetch. DDR has two sets of data that are read and written to the memory core, while DDR2 allows for four sets of data to be processed. DDR2's internal data bus is doubled, which increases the die size. Although the die size is increased, the memory core internally operates at half the frequency. This allows DDR2 to run at the same frequency of DDR, but at twice the speed. For instance, DDR2 memory at 400MHz runs at the same frequency as DDR memory running at 200MHz.

A third difference is the write latency of DDR2. DDR's write latency is one clock. This allows for data to be written to the memory one clock after the write command has been issued. With DDR2, the write latency becomes two clocks. The doubled clock cycle allows for twice the data to be written to the memory after the write command has been issued.

A fourth difference is DDR2's new feature called On-Die Termination (ODT). ODT permits the user to terminate signals in the memory itself. The termination of DDR is done on the motherboard. ODT drastically reduces signal wave reflections from the termination network and promotes enhanced systems margins. ODT permits fewer capacitors and resistors on the motherboard, which helps reduce cost and makes memory subsystem layouts to be more efficient.

Why use DDR2?

There are several reasons why DDR2 should be considered. First, the required voltage is lower and reduces the system power demanded by the memory. Second, the increased pre-fetch produces a reduced core speed dependency for better yields. Third, DDR2 allows migration of higher bus speeds. Fourth, its write latency provides an improvement in command bus frequency. Finally, DDR2 provides additional features that improve the overall performance and effectiveness of the memory.

So why isn't everyone using DDR2?

DDR2's performance gains are not evident until you get to DDR2-533. In fact, it is not until you get to DDR2-667 where you begin to see measurable performance gains. This is due to the increase in latency that offsets any speed advantage until 667MHz. For the sake of comparison, DDR-400 outperforms DDR2-400 and runs comparable to DDR2-533.

DDR2 also costs significantly more than DDR. Since the 110nm fabrication process is far from standard, the cost of the DDR2 DIMMS is much higher and quantities are much more limited.

The true benefit of DDR2 is in its ability to achieve faster speeds with its lower voltage requirement. Eventually, DDR2 will make its presence felt in the marketplace, but it will be some time before the performance gains are truly realized.

To learn more about DDR2 and its specifications, AMD recommends contacting memory vendors who have developed or are developing DDR2 memory.

[enwar3]

thanks that answered my question!

[Godless]

basically DD2 has higher memory bandwidth

and as most people know AMD chips dont currently support DDR2

[rparadox]

Thanks for that well written piece of information. Very nice!

[Camaro]

basically DD2 has higher memory bandwidth

and as most people know AMD chips dont currently support DDR2

Very true However with AMD's onboard memory controller it can access memory faster then Intel using DDR2.

[brozly]

Next year.
Found a nice pdf. http://www.amd.com/us-en/assets/content_ty...yer_6-10-05.pdf

[Camaro]

Wow looking at onboard DDR3 memory controllers in 2007. Thats not so far away, but im doing my upgrading for the decade now

[Guest_m.oreilly?_*]

Next year.
Found a nice pdf. http://www.amd.com/us-en/assets/content_ty...yer_6-10-05.pdf

oh boy...

[Aries]

It´s coming sooner as we think. Amazing develpment. :D

Aries

[Fletcherea]

I remember reading about ddr2 awhile ago, and while upgrading my pc i decided, hey i should get some ddr2 memory while im at it! good thing i wasnt impulse buying and read a few articles 1st and found amd dont and probably wont use it, anyways, from what i read and researched, was that by the time amd starts using ddr3, 2007 as mentioned, ddr2 will just be being polished up and intel will probably ditch it(not completely of course, but focus more on the ddr3) to keep up with amd, ugh i always forget the point of my posts

[LPC]

Slightly off topic but the system bottle necks is still HD transfer speeds. On boot up / file transfer and loading apps it's the HD that slows everything down. I don't want bigger sized HDs and want faster drives. I'm talking about at least 3 times their current speed :).

[Camaro]

SCSI drives might do it for you then. But I understand what you are saying they have had how many years to develope faster rotation drives and they have 1 SATA 10k drive that stinks.

[Dow]

How can u say it stinks. I say the raptor drives work pretty damn well, exspecially in raid 0. The drives are the fastest sata drives on the market. They beat sata2 drives & they are just as fast as alot of scsi drives out there. Go WD, I hope they come out with a sata2 raptor with more cache. :thumbsup:

[brozly]

There is New technology out that uses "FirmWare" more or less as a cache.
* http://www.samsung.com/Products/HardDiskDr..._0000117556.htm

This post has been edited by brozly: Jul 26 2005, 10:51 AM

[LPC]

I think ya not following :).

Tansfer a file from a RAM disk to a RAM disk or from USB2 to RAM. 2Gb or so in under a second if the HDs don't wake up. Do it over the HDs and you looking and over 5 seconds ! That's what I'm on about. Busses :)

[fr0stb1t3]

I appreciate the DDR2 in my laptop for one reason only. It uses half the power of DDR1.

[Camaro]

How can u say it stinks. I say the raptor drives work pretty damn well, exspecially in raid 0. The drives are the fastest sata drives on the market. They beat sata2 drives & they are just as fast as alot of scsi drives out there. Go WD, I hope they come out with a sata2 raptor with more cache. :thumbsup: 

I think you missunderstood me, What I am saying is there is only one 10k SATA drive, well 2 if you count that they have the 36gb and the 74gb, but what I mean is other company's do not have 10k drives nor are they coming out with 10k sataII, that I have read about.
They make the interface faster but the drives themself are the same speed so you do not get any advantage.

[brozly]

Really, You would think the Raptors would at least be up to 15K by now. :(

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