So, I tried to upgrade my laptop (XPS Gen 2) From 1GB of RAM to 4GB.
Unfortunately, it turns out that the motherboard only supports 2GB. Right now, I have one stick of 2GB in there - but it's reporting that the chipset is running in "Dual Channel" mode. This is confirmed both in the BIOS and in CPU-Z.
Does that make any sense? Is it "assuming" that it's running in Dual Channel mode with 2GB installed?
Installing the 2nd 2GB DIMM results in the computer powering on for ~5 seconds (Hard Drive spinning, no display output) then shutting off. Installing one of the old 512MB DIMMs in there results in it booting and operating properly, but it "ignores" the second DIMM and reports only 2GB of RAM (CPU-Z only "recognizes" one module installed).