What happens when more RAM is installed than the motherboard supports?

"Simple answer: It either will only see the max supported memory or it will not work at all.

My gut feeling says two things:

If it does work, you just will not see the extra memory, only the max the motherboard/chipset supports. If it doesn't work, it usually will just beep at you with a memory error and you will get no video responce. All depends on the motherboard depending on how it handles memory errors.

Someone on Yahoo answers says an interesting bit about getting a blue screen due to this:

In my experience, putting in more than
the max amount of RAM as specified by
the manufacturer will cause the
computer to not boot up.

others claim:

Some won't POST, some will and simply
BSOD (kernel panic, etc) with
PFN_LIST_CORRUPT.

That said, the ""max"" memory isn't
always the actual max. Case in point,
Intel states the GL960 chipset (such
as in my laptop) supports a max of 2GB
of memory. 4GB is a no-go, but 3GB
works."

Depends on the board and BIOS. I have a Sony VAIO VGN-Fe770G that uses the GM945 chipset -- Intel, Sony, AND Crucial say that the maximum amount of RAM is 2GBs of DDR2 (1 GB per SODIMM slot), but I'm running Windows 7 x86 with 3GBs and both the BIOS and Windows report (and presumably map) all 3072MBs. I'm going to try with a second 2GB DDR2 SODIMM and see if the BIOS and a 64-bit LiveCD OS sees 4096MBs.

"Been there, done this. The BIOS complained about the RAM and refused to start up. I had to downgrade again. But this was an old Pentium 133 from Dell and about 4 PC's in the past.

In general, it will depend on the BIOS and hardware. It won't be able to handle the big modules but if there are still smaller modules available, the system might decide to just start up with the memory of just the smaller modules. But in general, the BIOS won't be able to use it thus your system would have no free RAM to use."

"I've done it on an older computer, and the computer booted just fine - however the BIOS / start up scrolling list only reported what the maximum for the motherboard was, so it was presumably ignored.

Now wether that's unsafe or not, i don't know, but i'd simply leave only up to the max in to be safe."

Assuming that you install the correct type that this motherboard accepts, anything above 2GB won't be addressed and will be ignored.