Dell Dimension 2400 and memory size capacity

Here's the answer to the issue of memory support:  If the main board supports the address lines to a given memory chip, then the chip will function at its capacity (i.e. 1GB or 2GB).  It appears that the main board of a Dell Dimension 2400 does provide addressing up to 2048 MB (2GB).  I say this only because some of you have installed 2GB and it seems to recognize that capacity.  Thus, there is an address line on the main board for 2 GB addressing .  The next address line, if present, would double the capacity of available addressing, allowing for 4GB addressing. The next address line would allow accessing 8GB, and so on.  The other problem then becomes a OS limitation.  XP, for example, could only access 4GB. 

As far as speed of the chip goes, most of the newer chips will provide backward accessing at slower speeds, as controlled by the CPU.