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alien
Oct 13, 2005, 08:46 AM
With all this talk about Dual Core G5s coming out soon, I have some general questions regarding Dual Core CPUs vs Dual Processor (single core) CPUs.

1) Its been explained before that a dual core would typically be 30-60% faster than a single core processor at the same mhz, but assuming that you had a single 2.3 ghz dual core G5 vs a 2.3 ghz dual processor G5, which computer would "thoretically" be faster.

2) With all the talk about dual dual core G5s coming out "soon", I guess the first question ties into this one... what programs could take advantage of the (essentially) 4 processors (if any), and if most programs can only handle 2 processors would it use the one processor (dual core) or two processors (single core).

I'm just trying to wrap my head around this dual core business before the possible G5 updates. Thanks.

robbieduncan
Oct 13, 2005, 08:54 AM
First of all a general observation: a dual-core (or dual-CPU) machine is only faster runnin multiple threads. A single threaded application (most games for example) will run at about the same speed on a single core (or CPU) machine as a dual CPU machine if all other things are equal. Some advantage may be gained as the OS can use one core or CPU whilst the single threaded process can use the other.

Onto your specific questions:

1) A dual-core machine should slightly out perform a dual-cpu machine as cache snoops between cores can be done on-die as opposed to going via the North bridge. In general usage this will probably not be noticable.

2) Any multi-threaded application should be able to use multiple cores. If you use activity monitor you will see many common OSX applications have many threads (a lot more than 2). All of these will automatically use as many cores as they can, up to the number of threads they have started. If there are 2 applications each with 2 threads then all 4 threads can run at the same time on a dual CPU, dual core machine.

Mr. Anderson
Oct 13, 2005, 08:55 AM
You already answered the first one - you'll see anywhere from 30-70% speed increase depending on the app so a single dual core will run 30 to 70% the speed of a dual 2.3

The thing is, you probably won't see single dual core's in the power macs which are the only one's with two cpu slots. So dual core chips in iMacs, PowerBooks, iBooks, etc will be great. The Power Macs will have 2 dual core machines so they'll be 30-70% faster than a similar 2 CPU machine with just single cores.

This is just a guideline - realworld tests will give us a much better idea on how well they actually perform - but regardless its the way to go in future chips. I'd love to see quad cores or more eventually :D

Now, as for the apps - things like FCP, Photoshop, iMovie and 3D apps, etc - Maya, Lightwave, Shake and other highly processor intensive apps benefit from more power, period. Any time you have to render video, animation or run a filter, the more power you have the faster it gets done - and on some of the pro apps I've waited over a week to get things rendered on my Dual 1.25 G4 - so you can imagine how interested I am in seeing a dual core PowerMac.

D

andiwm2003
Oct 13, 2005, 09:10 AM
.......................
1) A dual-core machine should slightly out perform a dual-cpu machine as cache snoops between cores can be done on-die as opposed to going via the North bridge. In general usage this will probably not be noticable.

......................................


access to the ram on the other hand should be faster on dual g5 compared to a single dual core because you have two channels. so the real world tests will show which is more iomportant.

but i also think the powermacs can only go dual dual core because the clock speed of the dual cores is about where the single cores are. in order to bring a substantial speed boost they have to go dual dual core (or lower the prices a lot what they never do). replacing the dual g5 with same clock speed single dual core g5s won't cut it.

savar
Oct 13, 2005, 09:32 AM
First of all a general observation: a dual-core (or dual-CPU) machine is only faster runnin multiple threads. A single threaded application (most games for example) will run at about the same speed on a single core (or CPU) machine as a dual CPU machine if all other things are equal. Some advantage may be gained as the OS can use one core or CPU whilst the single threaded process can use the other.

I know you know this, but just to be clear for the OP: Apps don't have to be multi-threaded, since processes can be doled out to different processors as well. So 20 single-threaded apps (as you alluded to in your analysis) could be divided across all four processors. Since the OS typically runs *many* background programs, pretty much all users stand to benefit from this, even if they are running only one single-threaded application in the foreground.

Also, I predict games go multi-threaded in the next 12 months. Parallelism will be required for Playstation 3 and XBox 360 development, so I see new games programming techniques transplanting to desktops as well.

Bear
Oct 13, 2005, 10:10 AM
A true dual core processor or a dual processor can actually wind up improving system performance by over 90% - it depends on what you're running however. (The usual about needing multiple threads or having multiple apps running at the same time.)

Some varients of Unix get 99% use of each additional processor(or core). Solaris on UltraSPARC III (or later) processors is one of them.