1GB and 256MB (Dual Channel) RAM Compatability?

On my Asus P5GD1 m/b I have two 256 DDR-400's installed for a total of 512 MB RAM.

Today I picked up two new 1GB DDR chips and tried to install them. I put the 1GB's in the blue (primary???) RAM slots and the 256 MB's in the black (secondary???) mem slots - but my PC wouldn't boot, and in fact it wouldn't get through the BIOS (ie no beep).

When I only install the two new 1GB mems the PC works fine and WinXP shows 2 GB of RAM. When I just install the two old 256 MBs the PC boots OK and shows 512MB of mem.

What's going on here? Can't imagine why these 2 different memory sizes won't work together...

 

Why even bother with the 256MB sticks? 2GB is plenty and hopefully they'll run in dual channel mode. You'll even be able to run tighter RAM timings - if you wanted to mess with that. Chances are, your PC would run faster with 2 1GB sticks in dual channel than the 4-stick combo you mentioned running in single channel. I can tell you that I personally wouldn't bother with them.

As Tony implied, that configuration may simply be "invalid" for that mainboard.

 

Well noted Tony and Chiles and thanks for the feedback.

I was able to solve my problem in different way. I tried installing the two 256MB's in another PC (for the kids) that already had 2 X 512MB's - and thankfully they worked perfectly in this PC for a total of 1.5GB.

Surprisingly the kid's PC uses the same m/b (Asus P5GD1) but for some reason these 256's seem to be more compatable with the two 512MB's.

I trust this is a good use of these 'spare' 256MB mems.