What Do Multi-Core Processors Do?

A multiple-core processor has multiple full-fledged microprocessors sitting there on the silicon die. For Core 2 Duo, if you looked inside on the chip, you would see that it is laid out with two processor "cores" inside. For a Xeon "Nehalem" you would see four. For certain in the Xeon "Westmere" line, you would see six microprocessor cores inside. So in this case, another core means another physical processor, sitting next to the other ones on the same silicon die.

even single core processors can execute code in more than one thread.

Well, yes and no. It depends on you closely you look. A single core processor can actually only be executing one thread at any instant, but in a multi-tasking environment, it switches around often, so it can make progress executing multiple threads over a fairly brief interval (in human terms) like in one second. A single core processor can only execute one microprocessor's worth of stuff -- whether that stuff is all in one task or it is switching around multiple times a second, executing multiple tasks.

A four-core Xeon processor can literally execute four instructions at the same instant, because it literally has four processor cores inside. It can multi-task on top of that.

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Now to make your head hurt. The "Nehalem" ands "Westmere" processors can do a thing called multi-threading. Each processor is so much faster than the caches and interfaces that it can pretend (with a Hardware assist) to be two processors, and execute two threads, each on alternate clock cycles. When such a Mac starts up, a Quad core reports it has eight processors. Activity Monitor shows eight processors. Apple System Profiler reports Quad core with multi-threading.

+I'm trying to weigh up the advantages of buying a Mac Pro over a different model like an iMac.+

I guess it really depends what you're looking for in your Mac. I really like the compact, sleek look of the iMac but the expansion potential is limited. Not everyone is into expansion, but the ease of adding hard drives and increasing memory gives the Pro a big edge.
I use mine for basic stuff including gaming, CAD & office applications so its a bit under used (for now)

AdColvin wrote:
@Casper_Cdn Yeah I'm not sure how much I would value expansion myself.

what programs are you going to run? what is your workload like?

what do you think you might like to run in the future?

multi-threading varies by application

Think of the system having reserved rights to 0, some background task(s) to 1, Safari on 2, etc. is one scenerio.

Some but not all or even a lot of apps are truly multi-thread.

Faster processor cores are still more important than how many cores.

one core with hyper-threading can execute two threads, and deliver 20-35% more in performance at the expense of running hotter and using more watts. HT came back in 2009 with Nehalem and Core i-Series.

Dual processor, two cpus, have been around for a long time on Macs back to G4/500DP and dual and quad-core is just more efficient to manufacture and build into systems (dual core Atom or A8's in mobile devices).

Programs that worked without HT sometimes don't work properly with H-T until they are recompiled and optimized properly.

Your real question is what Mac to buy though, and what you actually plan to run and do.

And there are processors for laptops, desktop, towers and more. And all have different performance.
http://www.intel.com/products/desktop/processors/index.htm

http://macperformanceguide.com/index_topics.html

Some iMac vs Mac Pro
http://www.barefeats.com/imac10o.html
http://www.barefeats.com/imac10v.html

So getting things to work in multi-core, multi-threaded, how much memory you want, the need for multiple drives (SSD boot drive and 1TB data drive even in iMac now), and graphic offerings.

Start with what you use, then to what you need to buy. Don't put the cart before the horse. A Mac Pro or iMac may seem at first to be on somewhat equal footing.

http://www.barefeats.com/wst10c2.html

There is a huge range in performance on MacBook/Air/Pro platform.
http://www.barefeats.com/mbpp31.html

Just a note to say that you should realize that none of Apple's computers have single core processors. The all have a minimum of dual-core cpus's, and some (including the top-end iMac) have 4 cores, some have 6 cores, and some (Mac Pro) have multiple 4-core or 6-core cpu's.

The 27" iMac with quad-core Intel i5 or i7 chips is a very capable machine. While certainly some people are better served by a Mac Pro (especially if you need more than 16GB of RAM or want very large on-board storage), the high end iMac is no slouch, and for much less than a high end Mac Pro.

You would find that CS5 working with large images benefits from large amounts of RAM; dedicated scratch; even Quadro 4000 to off load some graphics processing. All things you won't find on iMac. Want eSATA you can have OWC add one but they need to do it themselves.

Most times, if you have to ask, you don't need a workstation. Or you find you outgrow those all in one much sooner down the road.

Grand Central? good marketing name, and v. 1.0. I wouldn't say it or OpenCL are mature products. Too many Apple apps are memory hogs, not multi-core/-threaded even now.

And the number of developers that follow the rules and roadmap, will still get broken and borked with OS updates.

OpenCL should offer API's to run code as well as CUDA but it has a long way to to to catch up.

Yes an iMac will do find for some that won't need more than a basic desktop.

My 4.5 yr old Mac Pro can't take full advantage of today's GPU, Apple offers very limited no-choice choice in graphic cards, but with iMac you get what they have and that is it.

Ah, storage changes and improves and people even upgrade iMac, but to say never? really? I would never pay Apple tax for their slower SSD but those things are getting where $2K of SCSI use to go and beyond: 275-550MB/sec quiet, great for system or scratch purposes. Or you want a fast 3TB Hitachi. And where and how do you back that up? over one FW800? over eSATA? hope USB3 is offered? Things you can add later on a Mac Pro.

We get these "imac vs Mac Pro" all the time and I should learn to just ignore and let people try to do what they wanted but want someone to tell 'em its okay. Because if you can't tell from reading, you will afterwards.

I think dlloyd has done a great service with MacPerformanceGuide and if that doesn't answer questions with its tests and reviews then nothing will.