I am not a hardware person when it comes to computers so when I buy a new one I just pick the one with the biggest numbers, but I know I am most likely wasting money.
If you're going to purchase a new computer, what should you max out? Are things like the L2Cache (whatever that is) really important or is it processor speed? Is it RAM or hard-drive type?
Ram is the cheapest and best "bang for your buck" performance gain.
The l2 cache is built onto the processor, so that would go directly with the processor choice.
Processor can make a big difference depending on the type of work you do. A quick performance gain these days is to make sure you get a dual-core processor. Games will require a good video card and processor, video editing/processing will require a good processor focus and decent video card, and as long as you have sufficient RAM, just about any dual-core processor made today will support internet surfing/email/office/etc. everyday tasks.
This has been asked before, so check out these questions for more info:
https://superuser.com/questions/20807/best-hardware-changes-that-most-improve-computer-performance
https://superuser.com/questions/449/building-a-cost-effective-upgradeable-pc
Some other helpful tips: https://superuser.com/questions/302/tips-to-increase-performance-of-computer
Question about SSD's vs disc drives: https://superuser.com/questions/2347/should-i-get-a-solid-state-drive
https://superuser.com/questions/23487/recommend-a-hard-disk-drive
Others mention RAM which is also quite true. RAM is the most cost-effective upgrade/enhancement for "bang-for-buck" ratio. The second option others have mentioned is solid-state disk (SSD) drives, but your question seems geared more for the CPU/RAM/Chipset/bus rather than storage itself. SSDs are great but way too expensive. I'd have to say the biggest bang (overall) IMO is the integrated CPU memory controller.
For a long time, front-side buses (FSB) were a big deal as the FSB frequency (MHz) and bus width affected I/O from RAM to the CPUs. Nowadays, newer CPUs are putting the main meat of the FSB onto the CPU itself which is a huge performance gain.
Case in point: Intel Nehalem. AMD started using integrated memory controller (IMC) years ago back in 2003/2004 for their Opteron line and I believe passed it onto Athlons and the like. Intel? Nope. FSB all the way. They stuck by the FSB and simply tried to gain performance back by upping the L2 cache to make up for the slower I/O. The outcome from those few years? Intel was struggling to keep up with AMD in terms of price/performance. Now? Oh look - Intel has finally put an integrated memory controller on Nehalem. How quaint. Now everyone loves Nehalem.
For years, AMD has used IMC and with it been able to meet if not exceed a large portion of comparable microprocessors from Intel with lower clock speeds, slower/cheaper RAM and typically less power. Nehalem performance-wise is a great CPU. Until you factor in the costs of a newer chipset, newer RAM and the energy required to run the thing, then the "bang for your buck" picture starts to look a little foggy.
So for me "bang for the buck" in CPU terms means solid performance, overall costs (AMD tyically wins this battle), low energy costs and affordable/stable RAM compatibility. Other people may interpret differently, but I find it easier (and cheaper) to live by this set of principles/mantras/whatever. My wallet is a little heavier and the TCO of the computer itself will always be less rather than choosing speed/uber-cool/energy-guzzling/premium-priced components.
Edit: I realize I sound like an AMD fan-boy and to a certain degree, I fully admit I am one. I just wanted to point out IMC architecture and its huge effects on the CPU performance and how everyone seems to neglect its importance. It pays to pay attention to the minutia of technical details each vendor offers. I'm all for competition so having both Intel and AMD to me is a good thing. We as consumers need choice in the marketplace.
People are talking about RAM, but not saying why.
When you run a program, your operating system copies the program code from your hard disk to your RAM. The same thing happens if you open a file, or view a web page: the thing you're looking at on your screen has to live in RAM.
When your RAM gets full (because you're running too many programs, or have too many documents open), your operating system starts taking stuff out of RAM and putting it back on disk (in a "swap file"). If those bits of memory are needed again, it will swap something else out, and then bring them back in.]
This is slow.
If your computer is swapping, you will benefit from more RAM. A symptom of swapping is: you alt-tab to a window you haven't used in a little while and it is slow coming up, and your hard disk is grinding.
So, RAM-wise, you want enough to stop your system swapping. Over this point, you may get benefit from more, but it will be much less. How much is that? For typical Windows XP usage, 2GB. I have read that typical Vista usage needs 4GB. Personally, I doubt you'll get any benefit from more than 4GB unless you're doing something really memory-intensive (and, also, you need to be running a 64-bit operating system to even see more than 4GB).
It all depends on what you'll be doing on the new computer. Maxing out any or all of the factors you listed may or may not have a real effect on your computer's performance if you're not even reaching the limits of the computer's default configuration.
If you want real world noticeable performance (not so much in gaming), get a small SSD drive.
Buy a modest system, throw in a big hard drive for your media/files, and pick up a small 32gb or 64gb SSD drive. Due to the near zero seek times, nearly everything you do that involves any degree of I/O will feel snappy and make your PC a joy to use.
If your buying a new computer buy the one with the best processor the Pentium Core i7 if you can afford it or the new uprated 3.4Ghz Pheanon. The black series pheanons are excellent if you like to overclock.
You dont need a computer with massive amounts of RAM at the beginning, and as previously pointed out RAM is cheap, replacing a processor often means replacing the motherboard etc as well.
When it comes to upgrading again there is no point in going out and buying ram simply for the numbers, you have to establish your systems bottleneck as described by Amdahl's law. At this point its most likely going to be RAM or the graphics depending on usage.
It may not be "bang for your buck" but I find that the problem most "average computer users" have is that they don't know how to look after a computer. You need to be defragging fairly frequently (once a month of so for an average user), keeping track of what programs you have installed and deleting things you don't need, taking a look at what programs are starting up as soon as you start your PC and getting rid of ones that aren't necessary.
If you look after a computer properly it runs quite smoothly at little to no cost what so ever :) Of course, if you do look after it properly and want a hardware upgrade then RAM is definitely your cheapest option.
You can never go wrong getting the fastest cpu and hard drive / SSD that you can afford. You take care of those two components, there is nothing you cant do non-gaming related.
RAM is like air, money and women...you only notice it if you dont have enough.
Absolutely the best performance probably goes something like ram, graphics (if for gaming) CPU, hard drive. If your not gaming put the graphics after the CPU. If you've got money to burn Solid State Disks will shorten your boot times and load times for applications.
I think the sweet spot for a new PC would have to be... Core2Quad (don't need to max it out), 6GB Ram, 750GB HD, Any HD Video (I would purchase an aftermarket video card if you're looking to do any gaming). If you need more speed, it means you're probably running a lot of higher end applications all at once, so you should go with more RAM to see the greatest performance increase, but it's going to be cheaper from a manufacturer, such as Dell, to go with a faster processor.
This is for people looking to build their own PC's.
I'm going to have to assume you're looking for an overall good at everything, cheap yet powerful PC.
Current Sweet-spots for hardware:
www.newegg.com
Hard-Drive: 500GB-750GB ~ $.10-.14/gb SSD's are far too expensive if you want any storage capacity.
RAM: 8GB (2gbx4) $100-130
Processor: A little harder to figure. ~$220 Core2Quad w/ 12mb L2 -MB is more expensive, but still a better deal. ~$200 AMD Phenom II x4 w/ 2mb L2 (6mb L3) *You should look for these cache sizes because you get the highest performance boosts with the smallest jumps in price.
Video Card 1Gb of GDDR5 ~$150-190 (reviews are your best friend when picking which model, I prefer Nvidia)
For 'Bang for your buck' RAM is the clear winner - but... :)
In my experience the RAM clock speed makes a vast amount of difference. Upgrading from, say, 667Mhz DDR2 to 800Mhz does not sound much of an upgrade, but the speed difference is very noticeable.
So, in answer, a performance chipset capable of supporting faster clocked RAM would be my first choice, then choosing a processor with the most L2, not necessarily the the most Mhz 'per buck'. As previously (and eloquently) mentioned, this is one of the other, more overlooked, defining factors in performance.
For laptops, battery life is critically important. It doesn't matter how fast your computer goes if it's off when you need it.
