AMD/P4 Questions

[Molester]

ok, i know amd is double pumped, so 200mhz cpu frequency = 400mhz fsb, and having pc3200(ddr400mhz) ram will run 100% sync, but the P4 is quad pumped, so 200mhz cpu frequency = 800mhz fsb, but just about the best ram available is pc4000(ddr500), so what's the point in having 800mhz fsb if your ram will only do 500? this applies to the new AMD 64fx which can go up to 1600mhz fsb? what's the point?

[modenaf1]

hmmm, maybe this would go better in just the plain old CPU's area, but anyways, I think with the P4, it has memory dividers that do that, but even though the FSB is quad pumped, the memory is double pumped. I thought the new AMD k8's didnt have a fsb becuse of their "hyper Transport" and since the memory controller is integrated into the CPU. I REALLY am not that sure though, that is a VERy good question though, I look foward to hearing the answer, sorry though, the above is all i know about the subject :(

-f1
:cool:

[The Coolest]

well, I'm not too sure about the A64s, but the 800MHz P4s have dual channel DDR 400. so its basically 400x2 = 800MHz.

[Molester]

no no no, most boards today have dual channel, i have dual channel, but there is no quad data rate ram(ddr=double data rate, i.e. 200x2=400ddr), now, there is pc4000 which is ddr500, or 250x2, but no ddr800 or 400x2

[The Coolest]

dual channel acts as 400x2. so u get 800MHz fsb

[Molester]

oh, ok ok, that makes sense, but, if that's the case, what's the point in say me using dual channel mode, or, why can't i use some ddr200 ram running dual channel to use my 400fsb?

[The Coolest]

Only the latest Intel chipsets have actual Dual Channel DDR option, you also need two sticks of memory
and if you run a 400FSB P4 in such a board I guess you could use 2 PC1600 sticks.
Either that or I didn't understand your question.
If you're asking about the AMD, if you've noticed there's no real difference between dual channel and single channel in SocketA CPUs, that's just because they have double pumped bus, which means that one stick of DDR is enough.
I think that if u had 2 sticks of PC1600 you could run 200MHz in dual channel tho. I never heard of people doing this before though, and I still don't quite understand why.

[Molester]

exactly, my point is for the amd, let's say you set the cpu frequency to 200(double pumped is 400mhz fsb)

so, you could run 1 or 2 sticks of pc3200(ddr400) in single channel mode to run at 200mhz(ddr400mhz)

or

2 sticks of pc1600(ddr200) in dual channel mode to run at 100mhz(ddr200mhz), which when it comes out the back is 200x2 which brings it back to 400mhz

or

2 sticks of pc3200(ddr400) in dual channel mode at 50% to run at 100mhz(ddr200mhz), again coming out at 400mhz, which also means you could run tighter timings at lower voltages

should i start a new thread to get more responses on this?

[modenaf1]

Originally posted by The Coolest
well, I'm not too sure about the A64s, but the 800MHz P4s have dual channel DDR 400. so its basically 400x2 = 800MHz.

Oh yeah thats right! Pc3200 Ram is DDR 400, so 3200 Megabytes per second, but with the dual channel thats 6400, equaling that of the 800 Mhz quad pumped bus. But my question is, what happens if you only have 1 stick of ram? it dosent work nearly as well does it? becuase then you will only have 3200 Mb/s.

[Molester]

you would have to run at 50%

[hitechjb1]

The three posts pointed with arrows may be able to answer the questions in detils.

It discusses
- the AMD DDR vs P4 QDR, max bandwidth, effective bandwidth
- difference between AMD XP and P4 dual channel
- how to use low speed memory in ASYNC dual channel to match high FSB

Originally posted by hitechjb1
I have a number of posts about various aspects of memory modules and dual channel in a sticky in the memory section, posted during Feb - April 03. It seems that sticky is no longer there and the links to the posts do not work any more.

I found some copies of them and repost here.


Memory

RAS, CAS Timing and BIOS Memory Setting (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983755#post1983755)

Single Channel vs Dual Channel DDR Memory (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983759#post1983759) <-----

Overclocking memory module(s) vs dual channel (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983760#post1983760)

256MB vs 512 MB vs 1GB, 1 module vs 2 modules (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983763#post1983763)

Dual Channel Memory (1 vs 2 sticks, sync vs async) (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983766#post1983766) <-----

Dual Channel, Nforce2, P4 and AMD FSB (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983770#post1983770) <-----

Some Benchmarks of CAS Latency on Overall Performance (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983775#post1983775)

Different RAS/CAS timing on memory latency (estimate) (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983778#post1983778)

What is cycle time and frequency (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983779#post1983779)

Frequency, clock, period of synchronous operations, latency (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983780#post1983780)

Latency (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983782#post1983782)

Analogy on Bus Speed, Bandwidth and Latency (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983785#post1983785)

Analogy for FSB, CAS2, CAS3 latency and bandwidth for DRAM memory (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983786#post1983786)

Memory bandwidth efficiency (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1983791#post1983791)


For CPU, FSB, memory, ...

Summary for overclocking CPU and FSB (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1789454#post1789454) (page 3)

[Molester]

so i'm right in the sense that you can run 2 sticks of ddr200 ram in dual channel mode and get 400fsb or run 2 sticks of ddr400 ram in single channel mode and get 400fsb

my point is though, i already have pc3500(ddr433), and my timings are 11-3-3-2.5t, so if i run them in dual channel mode at 50%, i can have tighter timings, which would probably bring better performance, would it not? plus, i wouldn't have to do a volt mod on the memory voltage to get tighter timings or make it run faster than rated, right?

[hitechjb1]

Originally posted by Molester
so i'm right in the sense that you can run 2 sticks of ddr200 ram in dual channel mode and get 400fsb or run 2 sticks of ddr400 ram in single channel mode and get 400fsb

my point is though, i already have pc3500(ddr433), and my timings are 11-3-3-2.5t, so if i run them in dual channel mode at 50%, i can have tighter timings, which would probably bring better performance, would it not? plus, i wouldn't have to do a volt mod on the memory voltage to get tighter timings or make it run faster than rated, right?

Technically, the first sentence should read

so i'm right in the sense that you can run 2 sticks of ddr200 ram in dual channel mode with memory to fsb ratio 1:2, assuming 100% dual channel efficiency (comment: which is not the case in practice) and get a data rate equivalent to 400ddr or run 2 sticks of ddr400 ram in single channel mode and get 400ddr data rate.

What you suggested would work if the dual channel memory controller in XP and P4 are ideal with 100% efficiency. In reality, one would not get 2x bandwidth when running dual channel. Only about 75% for P4, and only 47%-78% for XP, of the combined memroy bandwidth of two memory modules. The above posts discussed these numbers in details.

E.g. DDR400 = 3200 MB/s
AMD DDR400 + DDR400 dual channel (SYNC) -> 95% of 3200 MB/s, or 47% of two DDR400
AMD DDR200 + DDR200 dual channel (ASYNC 50%) -> 78% of 3200 MB/s, or 78% of two DDR200 <--- efficient but not in absolute bandwidth
P4 DDR400 + DDR400 dual channel -> 75% of 6400 MB/s, or 75% of two DDR400

So if you run your PC3500 at ASYNC 50%, it is efficient if they were slow memory, but you actually lose in terms of absolute bandwidth from 95% down to 78% as shown above.


Whether one calls it FSB 400 or FSB 800, what is happening in hardware is that:
the clock frequency of the bus is still 200 MHz, but
- data is transferred at 400 Mbit/sec per line, twice the rate of 200 MHz for DDR400
- data is transferred at 800 Mbit/sec per line, four times the rate of 200 MHz in the case of P4 QDR800 (data only)

[Molester]

well, then what if i run my pc2700(ddr333) in dual channel at 70% w/ cpu frequency at 222, in other words, the ram would be able to run 155, but would only have a 111 load?

how would that run out?

[hitechjb1]

Adding PC2700 to the table,

E.g. DDR400 = 3200 MB/s
AMD DDR400 + DDR400 dual channel (SYNC) -> 95% of 3200 MB/s, or 47% of two DDR400
AMD DDR333 + DDR333 dual channel (ASYNC 80%) -> 90% of 3200 MB/s, or 53% of two DDR333
AMD DDR300 + DDR300 dual channel (ASYNC 75%) -> 88% of 3200 MB/s, or 59% of two DDR300
AMD DDR200 + DDR200 dual channel (ASYNC 50%) -> 78% of 3200 MB/s, or 78% of two DDR200 <--- efficient but not in absolute bandwidth
P4 DDR400 + DDR400 dual channel -> 75% of 6400 MB/s, or 75% of two DDR400

For AMD system, running ASYNC dual channel is mainly for reusing existing slow memory and when faster memory is not available to run in SYNC, the absolute bandwdith would still be lower than running SYNC.

The PC2700 in ASYNC mode comes close in bandwidth to that running in SYNC, 90% vs 95% at same FSB as shown above. But ASYNC would allow higher FSB.

If you have PC2700, try to overclock the memory and run them in dual channel like this
- in SYNC (with lower FSB),
- in ASYNC 75% or 80% (if motherboard can run) with higher FSB,

Test both of them w/ some benchmarks on bandwidth and 3DMark02/03. Would be interesting to see how they compared. Many believe that ASYNC would not perform as well even FSB can be clocked higher.

[Demont]

If I understand this correctly... you are saying run the FSB higher than the memory but use dual channel to pick up some memory bandwidth, right? Well I did have this idea a while ago, as well as a few others, and a guy I discussed it with did some testing here:
http://www.deep-powder.net/OC_Guide/Mem_Mobo_CPU_Overclocking_Guide.htm#dualddr

The closest test to your example was 194FSB & 156 memory speed. From single channel to dual channel there was a ~300/300 point boost in sandra memory.

As hitech was saying in one of those linked threads, dual ddr does not do much at a 100% (or 1:1) ratio. However, if you have some older memory and an NF2 board you can definatly make the most if it by running the FSB as high as possible and enabling dual ddr.

[edit] I have tested it myself hitech, it does work.

[Molester]

well, i'll do my testing after work, it all came up on me when looking at a P4 computer and started thinking about the 800mhz fsb, thinking that ram is only up to 500, it was then i read it was the dual channel that doubled the 400 to 800, so it made me realize you could run 2xddr200 on dual channel to get a 400ddr data rate, though the efficiency is down, you can pick it up by running say pc2700 at 70% to pick some of the efficiency back up, but i'll find out tonight

only thing i worry about is if the board will run async, it has the option, but......

[hitechjb1]

Originally posted by Demont

...
As hitech was saying in one of those linked threads, dual ddr does not do much at a 100% (or 1:1) ratio. However, if you have some older memory and an NF2 board you can definatly make the most if it by running the FSB as high as possible and enabling dual ddr.

[edit] I have tested it myself hitech, it does work.

I know it works, I tested myself a while back. I think most effective to observe this effect is to run FSB at 200 MHz w/ PC2100 memory overclocked to around 150 MHz using a ASYNC ratio of memory:fsb = 3:4.

Definitely it boosts memory bandwidth a lot.

Question is whether this dual channel ASYNC 3:4 setup by running high FSB with slow memory would help performance for actual applications, even just benchmark numbers for 3DMark 02/03, ... Some believe that beyond memory bandwidth, it won't help much.

If you have these data, pls post.

[Molester]

ok, well, did just a few benchmarks w/ my pc3500(ddr433) ram running at 75% of 222, equaling 166mhz in dual channel mode, and it was a significant drop in performance, but, if all i had was pc2700 ram(ddr333), i could see how this would be better than running a 333fsb

[hitechjb1]

Originally posted by c627627
I can do 208 FSB with my PC2100 RAM set to auto or 152 FSB with it set to 100%.

I could also do 204 FSB at 75% Memory Frequency which is 204 x 0.75 = 153

The best thing to do in real life appears to go with 100% although some benchmarks would indicate otherwise. Here's the thread where I did the testing at various Memory Frequencies:

http://forum.oc-forums.com/vb/showthread.php?s=&threadid=215500
...
Originally posted by c627627
3DMark2001SE
default everything no tweaks

At 100% 153 FSB x 15 [2295 MHz] with memory bus 153........12113
At 75% 204 FSB x 11 [2244 MHz] with memory bus 153..........11852

At 100% 150 FSB x 15 [2250 MHz] with memory bus 150.........11969

So what would be your final choice for FSB, multi and % ?

c627627 prefers to run 153 MHz in SYNC mode than 204 MHz ASYNC 75%, he said the 100% SYNC even with lower FSB would give better performance in real life.

Hope you can confirm or disprove his finding, not just by memory bandwidth (which is obvious), but by some other applications and benchmarks (3Dmark01/03, PCmark, ...).

[Demont]

It's all there hitech, in the link I provided above.

At the maximum asynchronous setting of 97Mhz for the memory speed, the performance gain of dual DDR over nondual-DDR configured memory as reflect by Prime95 is ~23%. At a synchronous memory speed of 194Mhz, the percentage improvement in Prime95 is ~8%. 3DMark2001 does show some performance improvement at lower memory speeds but these do vanish at synchronous speed. I would wonder about the use of 3DMark2001 as a tool to benchmark dual DDR.

[Molester]

like i said, from my tests w/ my pc2700, if all you have is like pc2700(ddr333) and you can get your fsb to 222, then running assync(75%=166) will run better than running a 333fsb w/ sync memory