Will DDR 512MB PC2100 work for a PC2700 PC?

It should work, youd have to check your motherboard, though if it works all your ram will run at the lowest speed(as will your processor) in this case 2100. I'd say the extra ram is worth the performance hit

looking at the dell site (http://www1.us.dell.com/content/products/productdetails.aspx/dimen_2400?c=us&cs=19&l=en&s=dhs&~tab=specstab#tabtop) would say yes it will work

I don't see that it would work on that site,,,,if it try it, will I blow anything??

Yes it will work but if you use both sticks it will show it down to the pc2100 speed.

There are no real compatability issues with speeds of normal DDR ram. You can mix and match its speeds but its gonna run it all at the slowest speed of ram you have. So you could get the fastest DDR and put it with pc2100 and it will run at pc2100.

Hope this helped :)

OK, now,,, does it matter if I put 512MB in front of 256MB?

Not at all, arrange them in any way you wish.

Umm considering I have run rams at different speeds, it will work.

Maybe you could tell me what experiences you have had, because I've done it ands its worked with absolutely no problems.

I have a Dell 2400 also.  I have not mixed RAM in a bit - but if memory serves, Bank 0 should have the lowest rated stick in it as when Windows starts up it sets it speed based on the first bank of memory it encounters.  I did not follow my advice on an old p3 I had and enjoyed the speed increase - but once in awhile I would get corrupt data due to the mixing.  It was not critical, because I was running mulitmedia apps - but I would say that it would be best to place the lowest rated speed stick in the first bank of memory.

Well people, As you can see, I've gotten different answers. So, I tried it, and,, ouch,,,I had trouble with PC. Maybe mixing DDR would work with a different mother board! I'm going to give points out the best i can.

Hello davekuhar,
Thanks for points.