Why DDR3?

[emilyek]

What's the deal? DDR2 hasn't been around that long, and it wasn't much of an improvement, if any, over DDR, and now we have DDR3.

Is this just to force upgrades? I mean, really.

Can anyone explain the necessity for DDR3?

 

[Roguestar]

Because it's a better standard and offers increase efficiency and throughput, whilst adding the possibility for higher speeds at low voltages. And from a beauraucratic point of view, because the JEDEC specification for DDR2 only went to 800 so we needed another one to kick in at this point anyway. It's like asking the question why DVDs over CDs, because most of the stuff you need to burn is around 600MB.

 

[DarkManX4lf]

Since DDR3 and DDR2 are both 240pin do they both have the same layout? Will motherboards support DDR2 and DDR3 on the same slot?

 

[krotchy]

Originally posted by: DarkManX4lf
Since DDR3 and DDR2 are both 240pin do they both have the same layout? Will motherboards support DDR2 and DDR3 on the same slot?

no, they are different specifications for timing and signaling etc. so they are keyed differently to prevent accidental insertment into the wrong type of slot.

 

[Roguestar]

They have the notches on the actual DIMMs in different places too.

 

[krotchy]

Originally posted by: Roguestar
They have the notches on the actual DIMMs in different places too.

thats what I meant by Keyed

 

[BladeVenom]

It's mostly just to sell people new hardware.

 

[SonicIce]

Originally posted by: BladeVenom
It's mostly just to sell people new hardware.

ding

 

[DarkManX4lf]

damn that sucks..

 

[Aluvus]

More bandwidth, less power.

 

[myocardia]

Originally posted by: BladeVenom
It's mostly just to sell people new hardware.

Here's another vote for "we don't have enough of your money (yet), so we're going to change something, to force you to buy something different." At least they're making each successive generation use less and less voltage. Of course, anyone that knows anything about Ohm's law knows that it won't necessarily use less power (watts), just because it uses less voltage.

 

[themisfit610]

Who freaking cares about memory bandwidth in the desktop PC market!!!

Beyond artificial benchmarks, there is hardly any improvement in using DDR2 vs DDR1, especially when we start looking at latency! Sure you've got scads more bandwidth, but guess what, that doesn't mean squat!

It's totally just an excuse to make people buy new hardware. Why did we need DDR2 over DDR1? Look at the performance differences between AM2 and 939 Athlons. VERY small. The same goes for Pentium 4's right when Intel jammed DDR2 down our throats, a bit more improvement in this case due to that processor's bandwidth hungry architecture. I would really like to see some head to head real world benchmarks between a Core 2 Duo running on dual channel DDR 400 vs DDR2 800. Something very CPU and memory intensive, like video encoding.

Of course, now DDR2 is stupid cheap, and DDR1 is all expensive... :|

Also

It's like asking the question why DVDs over CDs, because most of the stuff you need to burn is around 600MB.

That's not a good analogy IMO. There's a huge advantage in capacity and transfer rates when you compare CDs to DVDs (and now HD-DVD / BluRay). That's a real world advantage that 's easily measurable. This simply isn't the case with DDR2 vs DDR3.

~MiSfit

 

[Aluvus]

Originally posted by: myocardia

Originally posted by: BladeVenom
It's mostly just to sell people new hardware.

Here's another vote for "we don't have enough of your money (yet), so we're going to change something, to force you to buy something different." At least they're making each successive generation use less and less voltage. Of course, anyone that knows anything about Ohm's law knows that it won't necessarily use less power (watts), just because it uses less voltage.

Ohm's Law is not especially relevant; memory devices are not simple resistive elements, nor will I2R losses dominate. Power use will be dominated by the dynamic power use of the transistors, which increases with the square of voltage (and is also affected by transistor capacitance and frequency). If they were purely ohmic devices, and had a fixed resistances, power use would still increase with the square of voltage.

So yes, while it's possible to produce a net increase in power use (particularly since DDR3 has more buffer circuitry and fiddles with the termination scheme), it is unlikely.

 

[Roguestar]

Originally posted by: themisfit610

It's like asking the question why DVDs over CDs, because most of the stuff you need to burn is around 600MB.

That's not a good analogy IMO. There's a huge advantage in capacity and transfer rates when you compare CDs to DVDs (and now HD-DVD / BluRay). That's a real world advantage that 's easily measurable. This simply isn't the case with DDR2 vs DDR3.

~MiSfit

The point was that it was hyperbole to point out the fact that the differences aren't noticeable now. You might have thought that DVDs over CDs was a great advantage, because right now you have a need for more hard storage. Well, when you have a need for more memory bandwidth (and AMD systems seem to like it more than Core 2) you'll find DDR3 is the only thing at the top of the spectrum to fill your needs.

 

[c0d1f1ed]

Why DDR3? Because it's the only memory that can deliver the bandwidth required to keep a quad-core happy.

 

[corkyg]

I like BladeVenom's response - very true - and to carry that thought on, it keeps the company in business and people employed. All part of the economic engine that keeps geeks smiling.

 

[Oyeve]

Bah, I still use DDR1.

 

[themisfit610]

Why DDR3? Because it's the only memory that can deliver the bandwidth required to keep a quad-core happy.

What do you base that on?

I've had no issues keeping a quad core workstation at full CPU usage with both plain DDR2 and FB-DIMM.

~MiSfit

 

[Yellowbeard]

Keep in mind also that IC makers and IC density both play a major role in this. The memory companies build memory with the ICs that are available. If this was not the case, we'd still be seeing new memoyr built with Winbond BH-5 ICs. But, those were limited to 512mb. And, since when have you EVER been able to buy a 2gb kit of DDR memory for WAY less than $100? And, the natural progression of IC technology has forced the change from DDR to DDR2 and now to DDR3. 2gb of FAST memory is as cheap now as it ever has been so progress is not bad or evil.

I am not so naive as to think that money does not play into this but, technology and economies do not stand still. And, I still have not seen anyone being "forced" to upgrade. No one ever complains about how hard it is to find a good MOBO that will take RD-RAM or DDR1 and combine it with C2Quad and PCI-Express support. It's odd to me that the blame so often falls on the memory industry.

 

[c0d1f1ed]

Originally posted by: themisfit610
What do you base that on?

I base that on the fact that four cores can easily demand more bandwidth than DDR2 can deliver.

I've had no issues keeping a quad core workstation at full CPU usage with both plain DDR2 and FB-DIMM.

Are you playing silly? The slower the RAM, the higher your CPU usage will be. With more bandwidth, you'd be able to get higher performance.

 

[GFORCE100]

Originally posted by: themisfit610

Why DDR3? Because it's the only memory that can deliver the bandwidth required to keep a quad-core happy.

What do you base that on?

I've had no issues keeping a quad core workstation at full CPU usage with both plain DDR2 and FB-DIMM.

~MiSfit

You sound like a marketing person throwing out these catchphrases which aren't 100% true. CPU usage is not directly linked to memory bandwidth since if the code you want to execute in say a loop fits into the L1 or L2 cache, then unless that code needs to fetch more data, memory access won't matter and the CPU usage will be high anyway (depending on the code complexity).

On the other hand very few software these days fits into the cache hence memory bandwidth does matter, it depends on the given application. Try benchmarking say a video encoding test on similar machines with DDR1 and 2 and you'll see the difference, especially if the DDR2 machine is using low latency memory rather than 5-5-5-15 at 667MHz PC2-5300 for example.

 

[GFORCE100]

Originally posted by: c0d1f1ed

The slower the RAM, the higher your CPU usage will be. With more bandwidth, you'd be able to get higher performance.[/quote]

If the CPU is forced to wait on data from RAM then this inserts idle cycles into the core unless it can handle multiple threads at the same time in which case it will do something else in the meantime but this doesn't change the fact that the given initial op has to wait thus be delayed. How much idle states lower (not increase) performance depends on what execution is waiting to be completed in the pipelines as other ops might very well depend on the result of a previous op. They too can causes a L2 cache miss thus also require data from RAM. It's the main reason why the faster a CPU, the faster it's FSB (or HT) and larger its caches need to be to keep the data flowing through the execution units as effectively as possible. If CPU's only needed to depend on their own SRAM (cache) then PC's would be a lot faster.

Memory must scale with the speed of CPU's to not make what is already a bottleneck (2nd after IO performance) even worse.