When I got my first B&W G3 it had 1GB of RAM (4x256) installed, but only 512MB was showing up. When I put the same sticks into my G4 Gigabit Ethernet all 1GB showed up.
Maybe RAM density is playing a part here. I've been working with PCs for years but only came across density recently when upgrading a friend's PC. It had a crappy Foxconn mobo and wouldn't boot with the original pair of RAM sticks I got for it. If I put in one new stick and one old one it would boot but only half of the new stick was recognised. After some google-fu I discovered that some chipsets require low-density RAM. In other words more chips per stick. In this case, with 1GB sticks I needed chips on both sides.
Maybe RAM density is playing a part here. I've been working with PCs for years but only came across density recently when upgrading a friend's PC. It had a crappy Foxconn mobo and wouldn't boot with the original pair of RAM sticks I got for it. If I put in one new stick and one old one it would boot but only half of the new stick was recognised. After some google-fu I discovered that some chipsets require low-density RAM. In other words more chips per stick. In this case, with 1GB sticks I needed chips on both sides.