@ phelan:
Like I said, assume a 64-bit OS. I see you recommend 4gigs, but I'm asking why would I want more than that?

And if I would want more, how much is reasonable before things go overkill?

I'm seeing two new builds with 6gig RAM. Is that the sweet spot (anything more is wasted or not used), or just a bit of future-proofing (a bit is wasted but is "on stand-by" for future games/progams)?

I think 4GB is probably the sweet spot right now, but i7 systems use triple-channel memory, which for a high-end system implies 6GB of RAM. The additional 2GB costs less than $50.

I have 8GB on my current system (below).

I'm building a Home Theater PC.

Rather than buy new for it, I'm buying new for me -- CPU and Motherboard

My wife gets the my current CPU and motherboard.

The HTPC gets my wife's CPU, motherboard, memory.

I'm splitting my 8GB of DDR2 -- 4GB for me, 4GB for my wife.

I'm willing to do that for two reasons, I don't believe the extra 4GB adds anything. And, I think the memory runs faster using only two sticks (2x2GB) because I can probably use T1 timings. With 8GB, only T2 works (on AMD). On AMD stuff, minimizing the timings is important -- however, the memory speed is much less important -- so I'm sticking with DDR2 for now running at T1 (hopefully).

Putt'n my money where my mouth often is when I post here (I shoot for best "visible" performance/price overall)

I run 8gb in my system, never seem to use much over 3gb running win7 64bit

4GB is the sweet spot, but on Triple Channel i7 you either have 3 or 6, so that's why you are seeing six.

Simple reasoning: Most games are still 32bit, thus can not use more than 2GB RAM. Some are coded to support the "LargeAdressAware" function which allows them to use 3GB. A clean basic windows install without an unnecessary heap of tray icons and background programs (such as a good gaming setup should be) will never use more than 1GB RAM itself. So 4GB is the absolute max you might need.

Of course, some functions like "RAMDrive" would want more RAM, also there are 64bit Versions of Productivity Apps (Photoshop, Premiere, 3d rendering stuff) which can and will use more than 3GB RAM for a single program, so for that kind of work 8GB is sweeter. But this is not normal gaming rig stuff.

On the contrary, some games have bugs with 8GB RAM, best known with Arma2, for example.

The advantage of 64bit, even with 4GB RAM, is that you are not restricted to the 3.5 of 32bit AND as far as I know the GFX RAM also counted against the limit in 32bit systems. So 1GB GFX RAM and 4GB System RAM would mean only 2.5 GB System ram actually usable. With x64 you get all 5.

I can offer a bit of historical perspective:

My current (32 bit) PC is 4 years old now but it was top notch with 2 GB RAM when I built it. So as already cited "future proofing" is a viable consideration, to a degree (keeping in mind that "all glory is fleeting"). At this point in technology I would opt for a 4 GB build.

I also installed an SLI-cable gfx card way back when, but never did up it to full SLI, so would say that's a lower priority.

The pace of technology is even more rapid now then it was a short 4 years ago, so don't break the bank. Build a capable system now with perhaps just a bit more horsepower than you need and that's about the best you can do from a cost effective "future proofing" perspective.

Sales rep at Digital Storm could've sold me a SSD for the system they are building for me, but instead he told me the truth. He said I should wait to go with SSD. First, because they are currently extremely overpriced for the amount of storage; second, because they are not yet at the level of reliabiity as mechanical drives due to their new technology; third, because they don't speed up games (to the degree the human eye can detect) once you are actually playing them--they only noticeably speed up boot times. Since this is to be a pure gaming machine for me, he said he'd gladly take my money if I wanted one but it's a waste of money for my purposes.

Just telling you what sales told me. Had he been less honest and told me something different, I would've bought one at great cost. I also asked about water cooling and dual vid cards. He said water cooling is almost never necessary, that 99 out of 100 people who buy it don't need it. They WANT it because they think it's cool or whatever, or just want bragging rights with their buddies. They are glad to sell it to whoever wants it. Some people go all the way and have water cooling into their vid cards, not just the CPU. He said water cooling a vid card was totally unnecessary but he'd gladly sell it to me if I want it. He said 1000 watt+ power supplies are only needed if you're loading up your system with at least two high end vid cards in SLI or Crossfire. Otherwise, he said, 750 was more than enough to run everything with power left over.

I like this company (DS) more and more for their honesty.

If you really want a true, "scorch your eyebrows when viewing" gamer, go with XP64, 24-32GB of ram,
GTX 295 in SLI and dump ALL the game program into a V.R.D.(Virtual Ram Drive). LOTS of moola...the last time I looked, a "decent" 8GB module was going for +/- $600.

I have XP64, 8GB of G.Skill PC6400 @ 4-3-4-9 2T with a voltage bump and sometimes dump up to 4GB of program into a V.R.D. and it will literally fly. No swap or prefetch; however, it can be a real problem getting everything "synched". The V.R.D software is also a major consideration, especially if you want to save what you've run and what OS you will run it on. Depending upon the amount of memory your v_card has, 4GB of board ram would be the minimum. V.R.D just isn't worth the trouble on a 32 bit OS.

There are many free V.R.D. apps out; try one and experiment.

I would imagine that W7 would be even better, but I'm not up on any of the software working with W7. Anyway, I won't be migrating to W7 until after the first service pack is released.

Another way to increase gaming/application performance is to locate .exe and .dll files as close to the MFT as possible. That will cut down seek and prefetch times: Ultimate Defrag 2008 is excellent and no, "just" defragging a hard drive won't max out seek performance.

Depending where on the hd the software you want the most from is, you could also relocate the swap file to the middle of the platter, posibbly closer to said software.

The "last" consideration to think about is the software cpu intensive, gpu or both.

Just my 2 cents worth: and as always, your mileage may very.

plug_nickel (Al)