Ask Dan: Choosing a CPU

Publication date: 18 August 2008
Last modified 03-Dec-2011.


Big V8 or turbo four?

I am looking at upgrading my PC to make it fly with software like Photoshop and Premier Pro CS3. All the buzz is around quad-core CPUs and new Nvidia video cards, however I am starting to believe an overclocked Core 2 Duo and Radeon 3000/4000-series video card will perform the same or better at lower cost. The only games I play have very modest video requirements, so that's not a consideration.

The other improvement I plan is a 650W or greater PSU, and to use a scavenged SCSI caching controller and a bunch of Ultra-320 SCSI disks to speed up the video rendering.

What is you opinion of going fast dual core CPU/mid-range video card for multimedia production tasks?


If you're not playing recent 3D games, there's no reason at all to buy a recent 3D graphics card. If you've got some ancient card then by all means upgrade to a value winner like a Radeon HD 3850, but if the games you play run OK on your current graphics card, there's no need to upgrade at all. Every card on the market has been more than fast enough for just about any 2D task you care to name for many years.

Adobe Premiere has had some sort of support for graphics-card-accelerated effects for years now, but I think those effects are still very much the exception rather than the rule. Generally speaking, the CPU still does all of the heavy lifting.

(If you upgrade to a giant 30-inch monitor that needs dual-link DVI input, and your current graphics card can't output that, then you'll really need to upgrade. But dual-link output is pretty much a standard feature today, too; the graphics card companies don't go out of their way to tell you that their low-end models have it, but I think pretty much all of them do.)

The quad-core CPU, on the other hand, is quite justifiable for Photoshop and Premiere work. Photoshop uses multiple CPUs very well for all sorts of everyday tasks (not just the most heavy-duty filter operations), and Premiere can really load up multiple cores for rendering. Both programs will work noticeably better on a quad-core CPU than on a dual-core.

You'll never see a straight mathematical increase in performance in almost any task if you increase the number of CPU cores, so a stock-speed Core 2 Duo E6850 (two 3GHz, 1.33GHz-bus-speed cores, $AU247.50 delivered as I write this) will actually perform pretty well for Photoshop compared with a stock-speed Core 2 Quad Q6600 (four 2.4GHz, 1.066GHz-bus-speed cores, price only slightly higher than the E6850). But the Q6600 will still have a small, probably-noticeable edge even for Photoshop, if you do the CPU-heavy filter and blending operations. If the limiting factor is RAM, because you are for instance working with very large multi-layer images, cranking up the CPU power will of course have little effect.

The quad-core also ought to give you somewhat better system usability - less delay when you switch from Photoshop in the middle of some enormous operation, like panorama merging, to something else. Again, though, a significant portion of that delay is RAM-related; if you don't have a 64-bit system with a ton of RAM, stuff will be paged out of and into physical memory, and you'll be waiting for the swap file, not the CPU.

The balance moves further toward the Q6600 when you start looking into overclocking. The Q6600 overclocks very well - 50% overclocks, to 3.6GHz, are pretty unremarkable, though 3.5GHz is a better target for Joe Average - and the E6850 can go even higher, though its higher stock speed means it can't manage that large a multiple of its sticker speed. It's no big deal to get an E6850 up to 3.8GHz, though.

But four 3.6GHz cores will conclusively beat two 3.8GHz cores for Photoshop and Premiere, even if the 3.8GHz cores are running from a significantly faster system bus.

So, If I were you, I'd definitely drop the extra ten to twenty bucks to get the Q6600.

Note that the Q6600's advantage is only significant for people who're actually able to use all four cores. There are a few games now that can make good use of two or more cores - Supreme Commander, Crysis - but generally speaking, every core after the first one is still unnecessary for most gaming boxes, and more than two cores is complete overkill. If your game only uses one or two cores, then obviously two 3.8GHz cores are preferable to four 3.6GHz ones.

Even then, though, the performance difference will be too small to be noticeable, and there may be something else you do that'll benefit from more cores. If the quad-core CPU cost twice as much then this wouldn't be a good reason to buy it, but it doesn't.

So even if I were mainly just playing games, I'd probably still buy the quad-core CPU, so that the unused cores could be chewing away at the distributed computing project of my choice, and waiting for software that used them to come along.

It's usually not a good idea to buy hardware now for tasks you imagine you might be doing in the future; if it turns out that you do need that hardware later, then that's when you should buy it, and probably get a lot more for your money.

But in cases like this, where doubling your CPU cores is almost free - why not?


CPU goes in case, case goes in bar fridge

I'd like to install a Core 2 Quad CPU in a Silverstone ML02 slimline MicroATX case. Are the stock Intel heat sink and fan going to fit? If not, what would you recommend?


No, the stock cooler probably won't fit.

I think a Zalman CNPS8000 might work.

Note, however, that I don't have the parts to fit together here to see. Since the Zalman cooler is 62.5mm high all by itself, and the little Silverstone case is only 82mm high, then taking into account motherboard mounts, the thickness of the motherboard itself, and the height of the CPU in its socket, the Zalman cooler may in fact not fit.

And it'd be no good if the Zalman cooler just barely fits, since it's got a traditional top-mounted fan, which won't work right if the top of the cooler is hard up against the case lid.

My own solution to this problem would be to drill a lot of air holes, or chop one big hole, in the lid of the case at the appropriate location. I have a suspicion that doing this might void the warranty, though.

This super-flat passive Spire heat sink would definitely fit, but the slimline case very probably doesn't have enough air flow for it to keep a quad-core CPU cool. Or probably even a dual-core.

You could add more fans, or swap the standard ones out for high-powered ones, but that's a lousy solution for a lounge-room PC, which is I presume what you want this to be.

The really kinky solution would be to use some kind of water-cooling setup, with an external radiator.

You'd better not trip over the hoses when you're plugging things into the stereo, though.


The exception proves the rule

I have an nForce 590 chipset in my Dell XPS 710. I want to upgrade to four sticks of RAM, and I also want to get a Core 2 Quad Q6700 CPU.

But the AusPC listing for the Q6700 says it's "not suitable for nForce boards and 4 sticks of RAM". What happens if I have this configuration? Will it work?


While I'm generally nervous about saying that any particular CPU upgrade will work in a Dell, the XPS 710 was available with a Q6700 as stock equipment, so that ought not to be a problem.

The four sticks of RAM, though, could be.

It's a power issue, basically; four CPU cores and four sticks of RAM need more juice - when they're working hard, at least - than many motherboards can deliver. Perhaps Dell's nForce 590 board is better than average (ha!), but if it isn't then there's no guarantee that the computer will even work at stock speed, much less be overclockable. If this is the case then you may be able to underclock the RAM and/or CPU to get it to work, but this obviously isn't a good solution.

I think the stuff I wrote a few months ago about other nForce chipsets applies, here.

(Since I sent this reply to Henry, Aus PC Market have updated that piece of quad-core-CPU boilerplate text. It now says "Not recommended for use with 4 sticks of RAM on 680i and earlier", which gives a better idea of which nForce boards ought to work.)

Australian shoppers can purchase all sorts of PC CPUs and motherboards from Aus PC Market.
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