Multi core CPUs

[Franky]

Hello,

Nowadays most of the PCs have a multi-core CPU with a clock speed in GHZ. My question is about that clock speed and the cores.
For example consider a CPU which has a 2 actual cores and 2 virtual cores (e.g., Intel core i3) and the computer system properties shows the 3.0 GHz as clock cycle speed.

1- Does that (say) 3.0 GHz show the clock speed of each core (from that core i3 CPU so that totally speed will be 4*3.0 GHZ = 12.0 GHZ!?) or that 3.0 GHZ is the entire speed of all cores?

2- Do the virtual cores have the identical effect as the actual cores in performance!?

And as well as I have a question about ROM .
Do ROMs anymore exist in current new PCes?

Thanks.

 

[pbcopter]

Each core is clocked at the same speed, so that they are performing their functions at the clock speed of the processor.
3.0GHz is entire speed of all cores in your example.

Things occur in parallel (each core) it does not multiply the clock by 4 in the case of a 4 core processor.

Virtual cores do not have the same performance as actual cores but they do allow for some parallel processing.

True ROMs are not likely found in modern PC's but programmable ROMs are in the form of the BIOS.

 

[3D Jed]

1. I've seen some unscrupulous sellers on Ebay advertising amazing 6GHz computers (and higher), but when you read the spec you only get some old dual core Pentium that the seller says is 2 x 3GHz ie 6GHz. A rip off.

2. Hyper-threading may give extra cores, but they are not equal to real cores. I did a test a while ago using a quad core i7 930, with HT turned on + off in the BIOS. Using Cinebench (equivalent to video rendering), the scores are directly proportional to cpu power. Hyperthreading gave a 26% boost - see pic



all cores were at 100% during the test - the screenshots were taken after the test so cores on idle. BTW not all software is written to utilize multiple threads to 100%. You can compare different cpu's power on this site

PassMark - CPU Benchmarks - List of Benchmarked CPUs

 

[LMiller7]

The number of cores and the clock speed are independent specifications and there is no relationship between them.

When hyper threading is enabled for each core there is a real physical core and a logical core. The OS will see them as 2 cores. But the logical core doesn't have any processing hardware of it's own so can't directly contribute to performance. They do benefit performance under some situations for reasons that are quite technical which I will attempt to describe.

Older systems like XP had only limited awareness of hyper threading and prior systems had none at all. In these systems hyper hyper threading would often impair performance. Newer systems have a better awareness and hyper threading will be of benefit. But don't expect much, maybe 10-20% at most.

 

[3D Jed]

I'm not a gamer, but I seem to remember reading somewhere that games aren't very multi-threaded. Stuff I do uses all the cores/threads I can afford - video editing, 3D rendering etc. Look at the 3rd pc in this (rather old) video. The little squares are render buckets ie 24 logical cores. It's a dual Xeon Mac.

12 Core vs. 8 Core vs. 2 Core ? Cinema 4D Render Speed Test - Greyscalegorilla Blog

 

[Franky]

Thank you all.
The number of cores has been increased for performing parallel computing.
And also logical cores/threads again has been introduced for performing parallel computing when possible.
If so, so both multi-core and multi-thread (per each core) are useful just for parallel computing and just when possible. Yes?

 

[LMiller7]

Within reasonable limits having more cores will always be a benefit. But there is always a point of diminishing returns beyond which little gain will be noticed. Writing software that can take full advantage of multiple cores is difficult and as a result most software does not. You might have many applications open but most, if not all, are spending most of their time simply waiting for something to do. And as the old saying goes "All computers wait at the same speed".

Going from a single to dual core CPU will usually provide significant benefits, in system responsiveness if not in actual performance. With 4 and more cores benefits will be harder to find. Games will usually see little benefit, being more reliant on good graphics performance.

Of course there are exceptions, video rendering being one. These applications are very much dependent on CPU performance and developers do their best to take advantage of the CPU resources. As developers gain more experience with this and multiple core systems gain market share benefits will spread to other types of applications.

 

[Franky]

Thank you very much lmiller for the explanations.