do pentium chips take a performance hit if not run dual channell?

[TDiddy]

i have 2 pentium M laptops
1 banias 1.5
and 1dothan 1.7
i hear desktop p4s if not run dual channeled take a performance hit but do Pentiums M's as well?

 

[uOpt]

The performance hit is pretty much neglectable on my P4 2.8C. Very very application crack the L2 cache often enough to bother.

 

[TDiddy]

my question is about Pentium M chips.

 

[uOpt]

My point is that even with the desktop P4 the speed hit is not really noticeable, so it won't with the Pentium-M.

Didn't even know the Pentium-M has dual-channel support...

 

[Artanis]

Because they haven't

 

[uOpt]

Well, that clears up the question allright, then

 

[timfountain]

I don't understand the answers given here. The CPU architecture has NOTHING to do with the way that memory is accessed, which is through the Northbridge/MCH. If you used dual channel on a dual channel supported MCH then you will get about 10-12% better memory bandwidth. Whether that makes any difference at the application level depends one where the performance limitations are....

- Tim

 

[Artanis]

And what mobile chipset does actually supports dual-channel ?

 

[Mik3y]

they dont take a performance hit wtihout dual channel. just just dont have a performance gain wihtout it.

 

[charloscarlies]

Am I really reading this?

Of course P4's take a performance hit without dual channel....especially as clock speed ramps up. P4's need memory bandwidth...plain and simple.

But as for the P-M's I really don't think it would make much difference...a lot like the A64's.

 

[gobucks]

The platform makes a big difference. For example, a P4 is very much bandwidth starved. It's high clockspeeds require correspondingly high bandwidth. Since up until now, the P4's bus was able to scale faster than the memory it was using, dual channel was used. The gain from dual channel is pretty substantial, equating to somewhere in between 1 and 2 speed grades, i.e. 300MHz or so in performance. However, it is nowhere near as effective as actually doubling the memory speed. If the P4 could use single channel DDR2 800, it would be faster than dual channel 400.

Anyways, the PM runs at lower speeds with a smaller pipeline, so it is not as starved for bandwidth, especially with its large 2MB cache. As such, the design focuses less on being able to ramp up bus speeds. Since currently the PM can only go up to 533MHz or 400MHz, depending on the core, that bandwidth is much better used on single channel DDR2 533 or DDR400 rather than on dual DDR266 or 200. Of course, since there is no dual channel for the PM, this is a non-issue, but I thought maybe you would like to know why they did not offer it.

In general, if a platform has dual channel support, then running it in single channel is generally slower, although the amount depends on the platform. However, all single channel architectures are not necessarily worse than all dual channel ones - just ask a socket 754 owner. The great architecture of the A64 combined with the increased clockspeed over their 939 counterparts makes them just as fast.

 

[Artanis]

So the P4-M owner would't take any performance hit running single channel config. As I mentioned

 

[Stormgiant]

I have a Dothan 1.8 on my notebook, and occordingly to the benchmarks, my memory score is very low compared to dual-channel setup.

But in real life use, it doen't show, maybe because the diferent arquitecture as said before.

 

[BigBadBiologist]

We have no idea what kind of performance hit not having dual-channel is as the 855 chipset doesn't support dual-channel. I would imagine that it would help a little because the P-M has much higher IPC than P-4. Based on early overclocking results of the P-M, I would argue that a lot of the observed performance ramping of the CPU is bandwidth-dependent.

 

[rogue1979]

My wife has a P4 2.26B @ 3.3GHz.

According to Sandra the memory bandwidth in dual channel is approximately 3600/3600.

Single channel is 2100/2100.

If you use an application that utilizes memory bandwidth, this will make a large difference.

 

[w00t]

i just found out that A64's dont run much better on dual channel because they have a built in ddr thingy i will rember what its called 2 min later *still thinking* o ddr memory controler i belive it was

 

[aka1nas]

A P4-M would probably benefit more from dual channel as it runs at a lower FSB than it's desktop counterpart. I am pretty sure the P-M doesn't have dual channel yet.

 

[uOpt]

Originally posted by: w00t
i just found out that A64's dont run much better on dual channel because they have a built in ddr thingy i will rember what its called 2 min later *still thinking* o ddr memory controler i belive it was

My P4 2.8C also couln't care less whether I have my RAM in dual-channel or not. I didn't find an application (is is actual application, not benchmark) that would give me more than 3% speed.

Let's face it, a 512 KB cache is pretty effective, and if your program is accessing memory too randomly, then the dual-channel's behavior of transferring more data (whether you need all of it or not) partly eats up the benefit of more linear bandwidth.