What do multiple cores do for me?

[Juardis]

If I have a quad core running one program all 4 cores are used right? I think that's right. So if I run a game for example, it's going to use all 4 cores equally. In other words, the same code will run on all 4 cores unless the program is specifically written to execute some code on core 1 and some code on core 2 and some on core 3 and so on, right?

But what if I'm running say 4 programs at the same time? Is there any load shifting between the cores or are all 4 programs still going to try to use all 4 cores as much as they can? In other words, even though the programs are not optimized for multiple cores, is the chipset or core logic (or whatever it is that controls this) smart enough to recognize that there are 4 programs running and try to preferrentially execute one program per core or somehow balance out the usage?

 

[teststrips]

your initial thinking is incorrect. Unless a program is specificially written to be multi-threaded, it will only run on one CPU at a time. The system will likely cause the program to round-robbin around to all 4 processors, but one program wouldn't be able to take more than 25% of the system's CPU recourses (unless of course that program is a multi-threaded program)

One huge benefit to one program not taking 100% cpu power means that you'll have plenty to do other things. You'll be able to do many CPU intensive things at the same time (don't confuse CPU intensive with I/O intensive... as you're hard drive won't be any faster)

 

[Juardis]

your initial thinking is incorrect. Unless a program is specificially written to be multi-threaded, it will only run on one CPU at a time. The system will likely cause the program to round-robbin around to all 4 processors, but one program wouldn't be able to take more than 25% of the system's CPU recourses (unless of course that program is a multi-threaded program)

One huge benefit to one program not taking 100% cpu power means that you'll have plenty to do other things. You'll be able to do many CPU intensive things at the same time (don't confuse CPU intensive with I/O intensive... as you're hard drive won't be any faster)

So if I have a cpu intensive program running in the background (SetiAtHome for example), and play a cpu intensive game, they both will run just as fast as if they were the only programs running?

If so, then all those programs sitting in the system tray shouldn't cause a performance hit on your games (or shall I say, much less of a performance hit)?

 

[alg7_munif]

Check out this thread, there is a program called setaffinity that can be used to assign a program to a specific cpu core, I personally have tried and used the program, I found that the program is very useful.

 

[unclewebb]

If you have a single threaded task the Intel C2Duo will take that task and continually move it back and forth between the 2 cores to balance the temperature of both cores. It might show up as a 50/50 split in task manager but often times it is 60/40 or 70/30.

My testing seems to show that it is totally core temperature related. As one core gets hotter it automatically shifts more of the load to the other core.

For me this is the real benefit of a dual core over a single core. When gaming on a single core it takes that one core and runs it at full 100% load which makes your cpu run near its max temperature. By swappinig back and forth on a dual core, you end up with two processors running at part throttle so the temps aren't nearly as high as running the app on just one core.

In XP you can set processor Affinity in Task Manager which lets you choose which core you wish to run a process / app on. It's best to let the process run on both cores. There were some older apps that had trouble running on a dual core system so this lets the user just run it on a single core if needed to for compatibility.

I did a quick SuperPi test with two different instances of the program running.

2M took 45.7 seconds running by itself.

When I ran two instances of SuperPi, both set to 2M, it took 52.6 seconds on one core and 53.0 seconds on the other. On a single core system it would have taken over 90 seconds as they both shared the same core.

If you have specific multi threaded apps for rendering or encoding that you frequently use the quad core is the way to go but for most people, dual core is sufficient. The majority of software available is single threaded.

For gaming and running Seti@Home your computer should be a little more responsive with a quad core over a dual core at the same MHz but the difference in performance would be pretty minor. Dual cores tend to overclock higher than the quad cores so for running two single threaded apps you would probably be pretty much the same with a dual or a quad.

 

[Lucio]

Just to tack a question onto this, would a dual / quad core be more useful if say, you have one hard drive per core if they're coming from different SATA headers?

For example, I like to play games and listen to music at the same time, would two hard drives along with a dual core help make things virtually as smooth as having two machines?

 

[unclewebb]

For example, I like to play games and listen to music at the same time, would two hard drives along with a dual core help make things virtually as smooth as having two machines?

Let's see now. A nice QX6700 quad retails for $970.

Should I get one of them or a $29 MP3 player at Wally-Mart to listen to music on while I game!
I'll let you do the math on that one.