Diferences between DDR333 and DDR400 ???

[grecco_julio]

Let's say that I have the best computer avaiable. The Kind of DDR Ram (DDR333, or DDR400) in a computer matters that much in the performance? How much? 5-15% or 1-2%? Is Ram a bottleneck like a processor or not? Thanks for your knowledge sharing.

 

[Tahir2]

If you have the best computer available you would not be asking whether DDR333 or DDR400 was the best.

RAM is not the bottleneck but bandwidth. You have a fast processor that needs data - with slower RAM or RAM with bad timings it will take longer for the processor to receive the information.
It also depends on whether you are talking about an Intel or AMD system. Intel systems seem to perform a lot better with faster RAM due to the way the processor can store information in its cache... the Athlon XP chips seem more hampered with the FSB speed rather than RAM speed. Athlon64 systems do away with certain bottlenecks due to the memory controller being on die but they also have a large L1 cache which helps keeping the processors fed of data.

If you have a choice to buy RAM at this time then go for DDR400 as its price is similar to DDR333 at this time.

 

[ChrisRay]

The nice thing about Athlon systems is many of the processors come unlocked.

Usually faster memory can mean a faster FSB, Most Athlon XP tbredbs and bartons can easily do 400 FSB if you drop the multipliar. Which is more bandwith.

That being said, DDR400 is better than DDR333 most of time. Plus its not any more expensive.

 

[jvd]

Athlon 64s don't need tight timing. The faster the better . So cas 3 with loose timing will perform close to cas 2 .

P4s though need tighter timings. Thats becasue the latancy of the onboard memory controller is much faster than the p4s external one .


Look at it this way . kumusa has adata ddr 4400 ram that will overclock to 280-290 mhz . Running your chip with ram that fast and a ht that fast will result in the fasted cpu avalible.


Another example is my athlon 64 3000+ . Its default speed is 2ghz . WIth its ram at 250mhz instead of 200mhz it will out perform a 3200 which is 2.2 ghz and more cache (1 meg) with a stock 200mhz ram .

 

[grecco_julio]

I need to know if the 2MB Cache version of the Athlon 64 will be in stores until the end of August, because AMD is not doing 2MB Cache processors anymore, so, I have a DDR333 system and I need to know if I will need to buy a DDR400 Ram for a 512K Cache to my PC perform better. In case, If I buy a DDR400 with an Athlon 64 512K Cache in what % it will outperform a DDR333 with Athlon 64 512K Cache system?

Thanks in advance

 

[Guden Oden]

I'm pretty sure AMD has never done 2MB cache CPUs. Some Athlon64s, or more likely Opterons, have 1MB cache. The newer A64s seem to have 512k cache.

In the end though you shouldn't look at how much cache a CPU has, but at what actual performance it delivers (and at what price, unless you got an endless supply of money). Buy the fastest you feel you can afford, nevermind how much cache it's got.

 

[K.I.L.E.R]

You will also find A64's tend to have single channel memory.

I think P4 duel chan gives 3.2Gb/s while A64 single chan gives the same.

I know Opterons include deul chan memory at 6.4Gb/s. Massive eh? Rivals that of a P4 Xeon.

 

[akira888]

You will also find A64's tend to have single channel memory.

The Athlon FX and the new Socket 939 Athlon 64's (3800+ and above) have dual channel memory controllers.

 

[Quitch]

Let's say that I have the best computer avaiable. The Kind of DDR Ram (DDR333, or DDR400) in a computer matters that much in the performance? How much? 5-15% or 1-2%? Is Ram a bottleneck like a processor or not? Thanks for your knowledge sharing.

Basically, for optimal performance match your RAM speed to your processor's FSB. If your motherboard supports dual channel memory, then buy a matched pair and you can double the number of FSB you're looking at (so DDR400 dual channel memory would be best paired with a processor with 800 FSB).

Benchmarks tend to show a small performance gain if you go for memory one step faster than your FSB, but after that you gain almost nothing.

 

[K.I.L.E.R]

You will also find A64's tend to have single channel memory.

The Athlon FX and the new Socket 939 Athlon 64's (3800+ and above) have dual channel memory controllers.

That's the chip over $1000 over here.

 

[PowerK]

Athlon 64s don't need tight timing. The faster the better . So cas 3 with loose timing will perform close to cas 2 .

P4s though need tighter timings. Thats becasue the latancy of the onboard memory controller is much faster than the p4s external one .


Look at it this way . kumusa has adata ddr 4400 ram that will overclock to 280-290 mhz . Running your chip with ram that fast and a ht that fast will result in the fasted cpu avalible.


Another example is my athlon 64 3000+ . Its default speed is 2ghz . WIth its ram at 250mhz instead of 200mhz it will out perform a 3200 which is 2.2 ghz and more cache (1 meg) with a stock 200mhz ram .

It's opposite, jvd.

Pentium4 likes bandwidth while Athlon64 likes tight timings.

This is because of Pentium4's deep pipeline hence higher bandwidth helps its somewhat deep pipelines. (more work done per cycle).

Athlon64 is not really sensitive to "bandwidth" of memory. This is why dual-channel configuration doesn't benefit Athlon64 system as much as it does to Pentium4 system. Athlon64 is very sensitive to latencies/timings.

 

[K.I.L.E.R]

Don't mind JVD, he enjoys talking out of his ass.

 

[PowerK]

K.I.L.E.R

can you tell us why you think I enjoy talking out of my ass ?

BTW, did my post above offend you in any way ?

 

[fallguy]

He said jvd, not PowerK. How can you get the two mixed up?

 

[PowerK]

umm... it's 4:30 AM here. Forgive me. That was a clear sign, I needed to go to bed.

 

[Gubbi]

There seems to be alot of confusion in this thread. Both processor types likes bandwidth. You need to get your data in and out of you chip to do your work.

However the on die memory controller of AMD's chips means that it has much lower total main memory latency. This means that the majority of the latency is made up of the latency inherent in the memory modules. P4s on the other hand uses an external memory controller in the chipset northbridge. This increases the total main memory latency (actually nearly doubles it). This means that improving memory module latency by say 33% in an AMD system you'd see close to 33% overall latency improvement, whereas in a P4 system, improving memory modules latency by 33% you see less than half that improvement because the latencies involved in the CPU<->chipset communication is fixed.

So yeah, Athlon 64s are more "sensitive" to latency than P4s (a better way of saying it IMO is that A64s can make better use of improved memory latency).

Both processor architectures use prefetch mechanisms to lower the latency the processor sees, by guessing where the processor will request data from. This means that when the processor request a chunk of data that is not in the on die caches the memory subsystem might already have fetched the data anyway.

This is why you'll see latencies cited in various reviews in the 40-50ns range for A64s and 70-90ns for the P4 where the actual latencies are in the 70-100ns range for A64 and 170-200ns for P4s.

However, the downside to prefetching is that quite often the CPU/chipset will have guessed wrong and fetched data that won't be used and hence wasted bandwidth doing so. The more aggresive you prefetching becomes the more bandwidth will be wasted. So you can trade off bandwidth for latency. This is probably why the P4 is seen to like bandwidth: the excess/spare bandwidth is used to fetch data speculatively to improve perceived latency.

Cheers
Gubbi