Old CPU + new Mobo: What RAM?

I have not built a system in 5+ years, and never used Intel processors. Since I come from the ancient world of AMD Athlon XP processors and DDR1, what kind of memory do I buy for this setup?

I want to use a P4 2.8GHz /1mb/800 that I got for free from work. I am going to buy a LGA775 motherboard so that I can use the P4 for now and upgrade to a Core 2 Duo/Quad in a year or two.

The mobo: Gigabyte GA-EP45-UD3L link
I will be running XP SP3 (32bit).

From what I've gathered, this P4's "800" rated FSB is really quad pumped, so the mobo would be running a true FSB of 200MHz. The mobo I'm buying only supports DDR2, so for now, I think the minimum I need is DDR2 400, but I've heard that it is slow and not worth it. So if I buy DDR2 800, won't it be significantly underclocked at only 400MHz? What the heck is this 1:1 thing I've been reading?

To make matters more confusing, if I want to O/C the P4 to ~250 FSB, that will put the CPU in the realm of 3.5GHz, and the memory at 500MHz. But this is still less than the DDR2 800 is capable of. Is DDR2 800 a waste of money?

Might as well buy DDR2 800 even if it would be underclocked in this application. There really doesn't seem to be any price difference between DDR2 400 and DDR2 800, plus DDR2 400 isn't available in 2GB sticks (at least from Newegg). Besides that, you'll be future-proofing yourself in case your processor dies and you buy a faster one.

Best thing is to buy 2 2GB sticks of DDR2 800 for now. That will only set you back about $40. The motherboard you linked to supports up to 16GB of RAM. However, unless you use a 64-bit processor and OS you won't have use of more than 4 GB (actually less due to the address space used by the PCI bus). If you later upgrade your processor and OS you can always get more RAM.

+1,
DDR2 is really cheap, can't complain about $40 for 4GB of it. Underclocking the RAM is fine, if your board allows...you can drop the voltage a bit since it runs slower and it will run cooler.
I am running a dual core Atom processor in my little box, it uses 1GB of DDR2 laptop memory. Next time I'm at the computer parts store, I am picking up a 2GB stick for XP. RAM is about the cheapest thing you can buy for good performance in your computer.

For the memory, you'll want to go ahead with the DDR2 800. Like jtr1962 said, you'll be future-proofing it.

I do think that you'd be better off not using the P4 though.

If you use this Celeron instead of the P4, the power-savings (if you leave the computer run for long periods of time) will more than make up for the added cost. The performance will also be much better than with the P4. The P4 is notoriously inefficient.The Dual-Core celerons are basically a cheaper version of the core 2 architecture, just with a smaller cache. Another great CPU would be any of the Pentium Dual-Cores (Wolfdale Core) like this one.

If you're going to wait a year or two to buy a better CPU, this would be a better way to go, as you'll be saving time and money in the long run.

On the other hand, if you just use your computer for surfing the web, checking your email, and writing up documents, you might also consider keeping your current computer and trying Linux. :shrug:

Well I'm not a total n00b, just new to how Intel motherboards use the FSB in relationship to the speed of the memory. I do IT work, and I'm quite familiar with Linux.

The main thing is, I'm on a limited budget, but I'm doing this build so I can get away from the AGP port and move to PCI express. So instead of buying a CPU like the E8400 now, I'll just use the P4 in the meantime to get the system up and running.

Now, if I get a new Core 2 (duo/quad) that uses, say, a 333FSB ("1333MT/s"), and I wish to over clock to, lets's say, 425MHz FSB, then won't I need DDR2 capable of 850MHz or better?

What I'm getting at is: For now I can buy a cheap stick of 2GB DDR2 800 to use with my P4, and then in the future when I buy a faster CPU, then I will get 4GB of DDR1000 or 1066 so I have room for overclocking. Does this all sound correct?

What is this 1:1 ratio thing? How does that work? Is there a BIOS setting so that you can tell the memory to run at a different speed in relationship to the FSB? That's foreign to me since the AMD CPUs I've used in the past have the memory controller built into the processor, and for all intents and purposes, the memory always runs at the same (well, twice since it's double data rate) FSB as the processor does. Intel confuses me. :candle:

I build at least a few systems each year, and I try to stay away from changing settings for memory. The best thing you can do is look at the recommended RAM for your MB, and buy that.

The RAM listed on Newegg is:
DDR2 1366(O.C)/1066

You might want to check the Gigabyte website to be sure that MB will be compatible with your CPU. I ran into that problem myself with one of the newer boards, where it says Pentium compatible, but it's only the new Core 2 architecture Pentium chips, not the older ones.

Here's a link to a page with lots of other links. If you do some reading, you should be able to get a better idea.