Questions about AM2 and DDR2 Memory

[bamacre]

My big beef, so far, with AM2 is the cost of DDR2-800 memory.

This is about the cheapest name brand 2GB kit of DDR2-800 I could find...

http://www.zipzoomfly.com/jsp/ProductDetail.jsp?ProductCode=85229

and 1GB Kit...

http://www.zipzoomfly.com/jsp/ProductDetail.jsp?ProductCode=85207

My questions are (not worried about OC'ing at all)...

1. Why is it that AM2/DDR2-800 performance is only minimally better than skt939/DDR-400 memory?

2. Do most AM2 motherboards support DDR2-533 and DDR2-667 as well as DDR2-800?

3. If #2 is yes, how much performance loss is there when using 533 or 667 instead of 800?

 

[imported_Questar]

1. Why is it that AM2/DDR2-800 performance is only minimally better than skt939/DDR-400 memory?

Because the K8 architecture is massivly sensitive to memory latency (a major issue IMHO). DDR2 has higher latency than DDR.

2. Do most AM2 motherboards support DDR2-533 and DDR2-667 as well as DDR2-800?

I'd bet all.

3. If #2 is yes, how much performance loss is there when using 533 or 667 instead of 800?

A couple of percent.

 

[o1die]

Believe it or not, Biostar has announced that they will use a via chipset for a ddr am2 board, still in the planing stage. I hope they do the same for conroe. But really, there's no point in mixing the am2 with ddr. If you want to use pc3200, you might as well get the regular athlon 64, as performance for both is almost identical.

 

[bamacre]

Thanks a lot guys. If I can use DDr2-667, that helps a lot.

 

[Aluvus]

Originally posted by: bamacre
1. Why is it that AM2/DDR2-800 performance is only minimally better than skt939/DDR-400 memory?

DDR2 trades improved bandwidth for inferior latency. K8 doesn't really need the bandwidth.

2. Do most AM2 motherboards support DDR2-533 and DDR2-667 as well as DDR2-800?

Yes.

3. If #2 is yes, how much performance loss is there when using 533 or 667 instead of 800?

The benchmarks here use several different speeds of memory with basically the same setups. They should give you some idea.

 

[lopri]

To get the facts straight, AM2 in current state is inferior to Socket 939 platform. (Except Sandra Bandwidth test) All these reviews compare DDR400 @2-2-2 with DDR2 800 @4-4-4, which is just a joke.

1. AMD enthusiasts = overclockers. How many people here have your RAM @200MHz (2-2-2)? PC3500, PC4000, PC4200, PC4800,.. have been out for ages. Decent DDR500~DDR600 @2.5-3-2/2.5-3-3 timing will mob the floor with DDR2 800 @4-4-4
2. Have you checked the prices of DDR2 800 with 4-4-4 timings? Good luck finding a 2GB kit (1GB x 2) for under $300.

Edit: I just double-checked and it looks like you can buy DDR2 800 (4-4-4) for around $250. Still expensive.

 

[imported_Questar]

Originally posted by: lopri
To get the facts straight, AM2 in current state is inferior to Socket 939 platform. (Except Sandra Bandwidth test) All these reviews compare DDR400 @2-2-2 with DDR2 800 @4-4-4, which is just a joke.

1. AMD enthusiasts = overclockers. How many people here have your RAM @200MHz (2-2-2)? PC3500, PC4000, PC4200, PC4800,.. have been out for ages. Decent DDR500~DDR600 @2.5-3-2/2.5-3-3 timing will mob the floor with DDR2 800 @4-4-4
2. Have you checked the prices of DDR2 800 with 4-4-4 timings? Good luck finding a 2GB kit (1GB x 2) for under $300.

Edit: I just double-checked and it looks like you can buy DDR2 800 (4-4-4) for around $250. Still expensive.

DDR2 800 at 4-4-4 has the exact same latency as DDR400 at 2-2-2.
DDR600 at 2.5-3-3 will not "mop the floor" with DDR2 800. Since it basically runs at 3-3-3, guess what? Exactly the same latency again.

 

[lopri]

So you're saying,

DDR400 @2-2-2 = DDR600 @2.5-3-3- = DDR2 800 @4-4-4 ?

Interesting.

Edit: For the record, I'm not the type that plays with timings all day long to gain 0.1 sec in Super PI. I'm bringing this only to point out the fundemmental flaw in AM2 reviews over the net. The benefit that DDR2 800 brings to A64 on DDR400 is, probably, smaller than what DDR600 (2.5-3-3) would bring. That was my point. Despite (or because of) this, reviewers are making such big deal out of benefit of DDR2.

 

[imported_Questar]

Originally posted by: lopri
So you're saying,

DDR400 @2-2-2 = DDR600 @2.5-3-3- = DDR2 800 @4-4-4 ?

Interesting.

Edit: For the record, I'm not the type that plays with timings all day long to gain 0.1 sec in Super PI. I'm bringing this only to point out the fundemmental flaw in AM2 reviews over the net. The benefit that DDR2 800 brings to A64 on DDR400 is, probably, smaller than what DDR600 (2.5-3-3) would bring. That was my point. Despite (or because of) this, reviewers are making such big deal out of benefit of DDR2.

Yep, that's exactly what I'm saying. Latency is measured in memory cycles. If halve the cycle speed, and the number of cycles you have to wait doubles, it works out to the same latency.

A big reason AMD went to DDR2 is becuase of cost. DDR1 began dying the day Intel switched to DDR2. AMD had to make the switch to keep system costs down.

In my opinion, the fundamental flaw in the k8 architechture is being latency dependent. Future memory bandwidth is basically unlimited. Future memory latency is only going to go up, and can never reach zero. That leaves AMD cpu performance dependent upon the one thing that can't get much better.

 

[soydios]

@lopri
DDR-400 at CAS Latency 2 has X number of wasted CPU cycles before the data from the RAM starts arriving.
DDR2-800 at CAS Latency 4 has the same number X of wasted CPU cycles.
Latency is the same. Bandwidth is higher with DDR2-800, though, which does improve performance somewhat.

Considering AM2 performance versus Socket 939, in games, real-world applications, and synthetic benchmarks:
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2762&p=5

OCZ Platinum XTC DDR2-800 2GB(2x1GB): $220
http://www.newegg.com/Product/Product.asp?Item=N82E16820227089
That's only about $20 more expensive than equivalent DDR1 memory. Expect prices to continue coming down (that kit was $250 three weeks ago).


@o1die
Socket AM2 cannot be made to work with DDR1 memory, no matter what chipset, because the memory controller is part of the CPU die.

 

[imported_Questar]

EDIT: Nevermind, I had a brainfart.

 

[lopri]

Sigh..
I know the frequency makes up for the latency. I thought we're talking about practice, not theory. Such as this:

http://www.anandtech.com/memory/showdoc.aspx?i=2560&p=7

They don't look exactly the same to me..?

My theory is in the first link you provided, soydios, if AT used a pair of DDR600 @2.5-3-3-7, the results would have been quite different. My guess is AM2 would not have had any win in the benchmark suit, except bandwidth tests. (Not that it's still a big deal.. Like I said, I don't care about 1~2% performance boost memory tweak could bring)
Also remember that the faster the memory runs, the faster the IMC will run. Often times we hit the clock wall of IMC before we hit the limit of modules.

Timings/frequencies are trade-offs, but somewhere along the line they'll split and I don't think DDR400 @2-2-2 can beat DDR600 @2.5-3-3 in most cases. So my question goes back to the reviewers. AT has been reviewing so many DIMMs with very well established format, why didn't they use more common (at least among enthusiasts) configuration like 275MHz (2.5-3-3-7) or 250MHz (2.5-3-2-5) or even 300MHz (2.5-4-3-7), while for AM2 review they pick such expensive and hard-to-find modules?

 

[lopri]

A quick search @the Egg brings up the following:

DDR2 800

The one you exampled has an SPD 4-5-4. All other 4-4-4 kits over $200, majority of them being over $250. So according to the theory, users will have to pay more for same performance. And in practice, I think users will end up paying more for less performance.

That's why I'm not too comfortable with all these AM2 reviews. I think I've seen only 1 site that presented honest data.

Edit: Another thing that I've just learned while reading on AM2 platform. Basically 1T command rate @DDR800 will be a luck of draw - means it'll be very difficult. With everything co-operating you'll get 1T with DDR2-800. But anything beyond that speed.. you'll have to live with 2T. Doesn't matter how many sticks you use, DS/SS, etc.. This one is also missing from the AT review. Why is it harder and harder to get a decent information on line?

 

[bamacre]

Originally posted by: lopri
A quick search @the Egg brings up the following:

DDR2 800

The one you exampled has an SPD 4-5-4. All other 4-4-4 kits over $200, majority of them being over $250. So according to the theory, users will have to pay more for same performance. And in practice, I think users will end up paying more for less performance.

That's why I'm not too comfortable with all these AM2 reviews. I think I've seen only 1 site that presented honest data.

Edit: Another thing that I've just learned while reading on AM2 platform. Basically 1T command rate @DDR800 will be a luck of draw - means it'll be very difficult. With everything co-operating you'll get 1T with DDR2-800. But anything beyond that speed.. you'll have to live with 2T. Doesn't matter how many sticks you use, DS/SS, etc.. This one is also missing from the AT review. Why is it harder and harder to get a decent information on line?

You know it seems to me, and I may be horribly wrong here, but many sites appear to be reluctant to speak negatively about AMD, and ready, willing, and able to do so with Intel. That said, since the births of the Opteron and Athlon 64, they haven't had a reason to bash AMD, and almost every reason to do so with Intel.

When Intel dropped prices on their 900 series Pentium D's, the talk was little, even though that opened the door to a plethora of budget dual core cpu's, running cheaper DDR2 memory. Benchmarks comparing the 900's with X2's have been anything but thorough, as well.

 

[jlbenedict]

thats the price you pay for wanting DDR2 800..
DDR2 speeds will increase over time..

Its the same now as when DDR first came to the market.. latencies were high.. speeds were nothing to write home about.. eventually, over time, DDR speeds were ramped up and manufacturing improved..

We are in the same cycle again, now that both Intel and AMD are on the DDR2 platform.. Its just something you will have to live with until we get further into the DDR2 cycle

 

[MrEgo]

I'm sorry for the thread hijack, but since we're on the topic of AM2 and DDR, I have this question:

Will AM2 CPUs work with DDR400 memory?

Also, I'm building a new system - is it a better idea to stick to 939 rather than go with AM2? I already have DDR400, so try and fit that into the equation.

Thanks guys!

 

[jlbenedict]

Originally posted by: MrEgo
I'm sorry for the thread hijack, but since we're on the topic of AM2 and DDR, I have this question:

Will AM2 CPUs work with DDR400 memory?

Also, I'm building a new system - is it a better idea to stick to 939 rather than go with AM2? I already have DDR400, so try and fit that into the equation.

Thanks guys!

The motherboards chipset implementation will determine whether its DDR or DDR2. I believe the chipsets designed for AM2 were designed to support DDR2, in mind. Basically... its all about the chipset.
I'm sure eventually there will be some odd-ball motherboard that will be AM2 based, and have both DDR and DDR2 memory slots..

 

[lopri]

AM2 CPUs don't work with DDR400 memory. Totally different platforms.

AM2 CPUs - NForce 500 Series or RD580 DDR2 boards
Socket 939 CPUs - NForce 4 or RD480/RD580 DDR boards

AM2 CPUs will work with DDR2-533, DDR2-667, DDR2-800. The only time AM2 has a chance to be faster than Socket 939 is when it's mated with fast DDR2-800 (4-4-4 timing). Even that can be neutered by fast DDR memory on Socket 939 platform.

 

[TomMe]

Originally posted by: lopri
Edit: Another thing that I've just learned while reading on AM2 platform. Basically 1T command rate @DDR800 will be a luck of draw - means it'll be very difficult. With everything co-operating you'll get 1T with DDR2-800. But anything beyond that speed.. you'll have to live with 2T. Doesn't matter how many sticks you use, DS/SS, etc.. This one is also missing from the AT review. Why is it harder and harder to get a decent information on line?

Where did you learn this? I was wondering about it..

 

[soydios]

@MrEgo
Again, Socket939 will only work with DDR1 memory. Socket AM2 will only work with DDR2 memory. This is because the memory controller is integrated into the CPU die. The chipset has nothing to do with it (you could theoretcially use Socket AM2 on an RD480 or nForce4 motherboard, because the CPU is responsible for the memory, all the Northbridge has to do is communicate with the CPU via HyperTransport).

 

[robertk2012]

Originally posted by: o1die
Believe it or not, Biostar has announced that they will use a via chipset for a ddr am2 board, still in the planing stage. I hope they do the same for conroe. But really, there's no point in mixing the am2 with ddr. If you want to use pc3200, you might as well get the regular athlon 64, as performance for both is almost identical.

your forgeting that amd will stop making 939 cpus soon

 

[Viditor]

Originally posted by: robertk2012

Originally posted by: o1die
Believe it or not, Biostar has announced that they will use a via chipset for a ddr am2 board, still in the planing stage. I hope they do the same for conroe. But really, there's no point in mixing the am2 with ddr. If you want to use pc3200, you might as well get the regular athlon 64, as performance for both is almost identical.

your forgeting that amd will stop making 939 cpus soon

Well, soon is after the end of the year...but your point is taken.

 

[lopri]

Originally posted by: TomMe

Originally posted by: lopri
Edit: Another thing that I've just learned while reading on AM2 platform. Basically 1T command rate @DDR800 will be a luck of draw - means it'll be very difficult. With everything co-operating you'll get 1T with DDR2-800. But anything beyond that speed.. you'll have to live with 2T. Doesn't matter how many sticks you use, DS/SS, etc.. This one is also missing from the AT review. Why is it harder and harder to get a decent information on line?

Where did you learn this? I was wondering about it..

http://www.xtremesystems.org/forums/showthread.php?t=100577
http://www.anandtech.com/mb/showdoc.aspx?i=2767&p=5

 

[A554SS1N]

Is it likely this DDR2 800Mhz 2T problem was just with preview/early samples of the CPU's?