comp config

Yes, I was pointing out the fact that it tells you exactly what type of ram you need for your dual processor mac. You have one choice... you don't need anything else. whereas on the pc, i still don't know what ram to get.

it's a pIII 866. i don't want to take my computer apart just to see what ram to get. damn the man.

If its a Pentiumiii 866 then I would guess it is pc133 Ram. That should be around 50-60$ for 256 MB. RDRam is for newer Pentium IV boards and pretty expensive. When you install it you have to open it anyways, so why not look before you go to the store?
Seriously though, everything you do on a computer is done in Ram or it gets sent to the swap space on your HD, so why not make your computer work faster by spending 60$?

My dad is buying the RAM for my birthday.

Why would Dell tell me I need one kind of ram if it's the wrong kind? just because it's more expensive? I entered my service number thing, and that is the ram it said I needed, and wouldn't it be bad to mix the types of ram?

The number I was looking for should be on the motherboard, and if you didnt open the case you probably entered the wrong number.... I am guessing.
Yes its bad to mix Ram like that. You can get away (though some say not to.) by mixing pc100 with pc133, but that is about as far as you would want to.

http://www.dell.com/us/en/dhs/offers/specials_m_dimen8250.htm
is this your board? This is what you would put RDRam into.
A 2.4+ GHz PentiumIV.

Basically the only way to identify what kind of RAM your motherboard can take is to look on the labels of the stuff thats installed.

Only way for me.

My system is a Dell Dimension XPS B866r.

The service number is a sticker on the side of the case that you enter to get your system specs, upgrades, etc.

I opened the case and looked at the ram, but it didn't really have any info on it.

I was searching around and they are right. You have a very nice system. I didnt think they made RDRam for Pentium III, but I guess they do. Do you only see 2 Ram slots? Does your Ram have a heat sink cover? If you can get as much Ram as your dad is willing to pay.

Yes, I only have 2 slots on the MoBo for RAM. And yes, they have heat spreaders on the chips themselves. It is a pretty blue color. Made by Samsung. Or Sanyo. I don't remember which.

Do i get the ECC or not? What's the difference?