I always assume they mean running more programs when using the word multitasking.
When one is running photoshop, autoCAD or other highly threaded applications, one does not usually say "I am multitasking". When one is running Chrome, Itunes, Word, and solitare, one would say "I am multitasking"/
Think on it this way. Say your running 4 single threaded applications on a C2D. You get moderate performance, but you want more. Ok, upgrade to a C2Q. Moderate gains. 100% utilization. Upgrading to a SB (more efficient) will give better results. Upgrading to a strait 8 core when they come out*, will not. You will still only use 50% of it at best.
* bulldozer is at best a threaded quad. They wont perform at the level of a true octocore processor.
That's all very well in theory, but you aren't going to hit 100% CPU usage running Chrome, iTunes, Word and Solitaire on even a dual-core CPU, much less a quad. In that kind of multi-tasking scenarios upgrading from a C2D isn't going to make a noticeable difference. As for your example, you're saying that I would get only moderate gains - however, if I upgraded, just as an example, from a E6600 to a Q6600, the performance would essentially double in heavy multitasking (the math doesn't quite work like that but you get the idea), which I think is a little more than "moderate". I would have to be going from a pretty darn good C2D to a lot lower clocked quad core to get even close to only "moderate" performance gains (like E8400 to a Q8200). And no, you won't get better results by just upgrading to SB. Going from E6600 to Q6600 would yield about twice the performance. So would going for a higher-end G600-series pentium (a SB dual-core) - that is, moving to a higher clocked, far more efficient architecture while maintaining the number of cores nets you around the same performance as doubling the cores on a 6 years older architecture. Impressive (and I definitely would take a G620 over a Q6600 simply for the single-threaded performance), but not better. It is only when you move to a more efficient architecture (like SB)
and starting throwing in the mix more threads/cores that you start to see actual significant performance improvements in heavy multitasking when compared to simply increasing the number of older, less efficient cores. But even then, it's a pretty unrealistic example. Most CPU-intensive programs are reasonably well threaded; you might run a heavily CPU bound application that can only utilise one thread, maybe even two, but using precisely enough CPU-heavy single-threaded applications to saturate a quad but not benefit from hexa- or octo-core is just unrealistic.
Don't get me wrong, though, I'm not saying that more cores rule all and single threaded performance is irrelevant (sometimes I ramble on so much one could get the wrong idea). But to say that multi-tasking isn't tied to the core count isn't right - like I sad, they're both as important. It's just that for the kind of multi-tasking you described, even increasing single-threaded performance isn't going to make a difference - that kind of stuff simply isn't CPU bound. It's when you start multitasking with heavier applications that the CPU power matters, and that's where the extra hardware threads are just as good as extra single-threaded performance. Like compiling, just for an example. Everybody likes compiling. I compile, you compile, everyone compiles (OK fine, just me then), and when I compile some really big piece of work I'm not going to stare at the screen for 20 minutes (or 2 minutes, or as hour), I want to get stuff done. Do some work without slow-downs. Perhaps play a game. Usually post on CF nitpicking and derailing threads. That's the kind of multitasking I'm talking about (not really running both AutoCAD and Photoshop at the same time, though I'm sure somewhere
someone does even that).
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