Influence of Dual-Channel?

Hi all, I was wondering how badly using unmatched memory chips would influence performance. Basically I was thinking of buying a single 1GB chip and use it along the 256MB that came in the Macbook (non-pro). Has anybody got any idea how big will the performance hit be?

I have no experience with Macs, but in my athlon-desktop I figured that having 1,5GB was way more efficient than having 512MB in dual channel most of the time, but it may be different with Core Duo and OS X.

 

I dono if that would run in Dual Chanal?

 

It's not going to run in Dual Channel at all.

it'll simply be a unmatched pair of memory.

I guess in the most basic sense to explain this is this way...

1. One 512MB ram will run 1x speed.
2. two matched 512MB (totaling 1GB of ram) will run 2x speed (this is dual channel)
3. two different sized ram (total ram will varie to whatever you got) will run 1.5x speed.

just think of it that way, obvisually you would want number 2, but if you can't afford it or whatever the case is then 3 is good.

now on a macbook the memory is shared so 64MB is assigned to the video on the computer so that leaves 448MB left for the system to use, any more ram regardless of if its in dual channel or not is going to help greatly. Its just common and good practice to have two paired same sized memory modules (same model and brand)

So really, more memory is better even if its in dual channel or not.

If someone wants a technical explaination of Dual channel just send me a PM and I'll tell you, or just ask here and I'll come back and do it. Didn't do it now becasue I don't have time too.

 

Don't worry about dual-channel. More memory is a much better trade off.

 

dual channel means nothing. Its always better to just have more memory.

 

You should just go for more memory, if you can get 2 Gigs and it will handle everything !
~Arman

 

Any performance hit will probably be compensated for with the increase in ram. I think dual channel makes ~2% performance increase, but that kind of seems optimistic.

 

Dual Channel does absolutely nothing - it neither helps nor hinders performance (AnandTech did a review of the MBP and proved that Dual Channel does nothing here). Go for more RAM if you want more performance.

 

Thanks for all the anwers, but I am still a bit concerned. Basically, I am on a low budget so buying 2 sticks of 1GB RAM is out of the question right now. I was thinking of buying 1GB of brand-named RAM now so that I could later try and find another one (besides, it's cheaper than 2x512MB sticks).

I am most concerned with the integrated GPU performance. Since it uses shared memory, it is said that the use of dual-channel is recommended for use with UMA (uniified memory architeture) for better performance/faster access to the system RAM to the 950 chip. But I couldn't find detailed benchmarks about it. The Macbook Pro has an X1600 ATI GPU so it's not nearly the same situation.

I tried to gather some insight about this comparing reviews of Core Duo's notebooks with the same specs bar for the single/dual-channel config- alas, I couldn't find a suitable pair, since most people use dual-channel. There is one review of a Dell E1405 with a single 1GB stick, and the PCMark05 scores seemed somewhat low - but I couldn't find another E1045 with the same amount of RAM/CPU speed AND running the same benchmark to be sure.

 

Dual channel isn't just a name...it does something.

Dual channel was designed to remove performance "bottlenecks." By using two identical dimms, the memory bandwith is doubled. A 1gb + 512mb PC3200 chip has a bandwith of 3200mhz. A 1gb + 1gb PC3200 chip has a bandwith of 6400mhz.

Just because the MBP in those tests was only using a fraction of the bandwith doesn't mean dual channel does nothing. It's like expanding a 4 lane freeway into an 8 lane freeway. With moderate traffic there will be no difference...in rush hour the 8 lane freeway is definately going to outperform its counterpart.

The problem is, when and how often is the MBP that congested? Dual core cpus are supposedly the first that can really make use of the bandwith...but you probably need to be using most of the system's resources. Most people will probably never see the benefits. It became popular because of gamers, who stress their computers, are in constant search of performance. The average joe on a mac will never know the difference.
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To the poster...Definately buy the 1gb stick right now. You'll leave yourself the option of just popping in another 1gb stick later. With two 512mb sticks, you'll have to remove one (read: waste $$$) when you add 1gb...and you'll only end up with 1.5gb total. I added a ram chip (of the same brand...not sure if that really makes a difference) two years after I made a computer and it ran dual channel, so don't worry about that.

Don't worry about the integrated GPU if you aren't going to game. The only lame thing about an integrated GPU is that it steals memory...but with 1-2gb it really doesn't make that much of a difference (especially with 2gb). The Radeon is faster (it is still relatively slow), but it runs hotter and consumes more power. It's a tradeoff I'd tip in favor of the integrated GPU...if you don't game or do 3d work (CAD, modelling).

1080p on my brothers coreduo mac mini just barely plays smoothly (it also has an integrated gpu). I think the gpu does mpeg2 and mpeg4 hardware decoding, so with a 1.83ghz+ cpu, you should be fine with video.

I wrote way to much...my fingers hurt. Good luck, man.

 

I can see that importing pictures into iPhoto might not stress the computer to its full extent, but wouldn't you say encoding is something as stressful as playing a game (in terms of the CPU and RAM, not the GPU)? Also, can you provide evidence/a link to support your argument? I would like to see a notebook that has dual-channel enabled outperform a notebook with it not enabled with similar specs. to the MBP. As far as I've seen, the only notebooks that have noticeably benefited are those with integrated graphic cards.

As for the original poster - the MacBook will actually see a small performance boost (probably not noticeable, however) as it has integrated graphics and is, performance-wise, bogged down a little with only one stick of RAM.

 

I prefer your analogy over mine, wish I thought of that one. Right now my Macbook is running with a paired 2gb and its sweet.

Since he is planning on a macbook here that 1080p is nothing you need to worry about because your screen resolution doesn't get that high on the macbooks lcd screen, unless you get an external that can support that high, and heck i dunno if the integrated video can even go that high.

 

If everyone uses DDR2 667mhz ram, no one will ever see a performance improvement. Dual channel doubles the memory bandwith, but the front side bus bandwith remains the same. If your ram is handing out data at (5333mb/s x 2) 10,666mb/s, the cpu can only consume it at ~5333mb/s.

Dual channel is only effective when the front side bus speed is higher than the memory speed. By doubling the bandwith of the memory under dual channel, the slower ram can better keep up with the cpu.

The macbook and macbook pros use a front side bus and memory speed both equaling 667mhz. Dual channel will do absolutely nothing for performance.

Dual channel was popular before the advent of DDR2. DDR chips max out at 400mhz, but FSB speeds of the P4 ranged from 400 to 800mhz. Dual channel was an effective way of relieving the bottleneck the ram was causing the cpu.

Dual channel isn't a gimmick...it just has it's own niche, one that isn't present in modern apple computers. It is a great marketing gimmick to the unwary, though.

Disregard my first post... I had to do a little research to get rid of the nagging questions in my head and I realized I had been under a misconception all these years. Hopefully this explanation is correct.

EDIT: It's still smart to use 1gb x1 over 512mb x2 just for economy. That part of my original post still holds true. Also, to anyone putting in unmatched ram, realize that the both sticks of ram default to the lowest speed. If you stick one 533mhz stick in with a 667mhz stick, both will operate at 533mhz.

Beyond that, any performance increase someone sees will merely be due to the increase in ram.

 

This make sense, but take notice that the main reason quoted for using dual-channel is the integrated 950 GPU. The extra bandwidth provided by dual-channel would be of use not to slow the GPU further, since its uses UMA. Since OS X both likes a lot of RAM and is somewhat graphics intensive due to QuartzExtreme, I am not sure how much of a performance hit this will be.

Here is aone of the few conclusive bits I managed to gather about GPU performance in dual vs single channel (from http://www.barefeats.com/mbcd3.html:

A 51% increase in Quake3 in decent, but but the GPU is too slow anyways to be used for serious gaming. Unfortunately the article does not specifies the test config. Anyways I am more interested in the effect on things like Exposé.

::UPDATE::
At last I found some concluding benchmarks here. They are from MacMini's but I guess it's close enough. There is a considerable performance drop (but if I understood the test setup correctly, the MacMini in dual-channel had 2GB of RAM while the other had 1GB+256MB) but in the Core Image Test the reported ~10% difference is more than acceptable to me. Thanks to everybody who tried to help.

 

Performance drop?

It sounds like your saying the macmini in dual-channel is slower than the unmatched memory.

 

You're right...the GMA950 does use all the bandwith provided by dual channel (~10.6 gb/s).

The macbook uses the intel 945GM chipset...which means it uses the mobile version of the GMA950 chipset, which is a neutered version of the normal GMA950. The clock only runs at 250mhz instead of 400mhz (pixel fill rate of 1000Mp/s vs 1600Mp/s). It's pretty freaking weak.

IMO, only go dual channel if its a convenience. Getting a 5 fps improvement is marginal, especially when the thing only runs games at 10fps in the first place.

As far as OSX goes, it runs perfectly fine with 512mb+. A 2% improvement (seen only in a few programs) is going to be unnoticeable. Upgrading just for dual channel is a waste, imo. To each their own, though.

I think this topic has been beat to death...

In most of the tests he linked, they were (marginally) faster. I think in one of them it was slower.

 

It should be noted that the requirements of the software on OS X and what they need should be taken into consideration as well.

When I put 2GB in my macbook the performance boost was astronomical, I wondered to myself how the heck I even did it with that 512MB.