I have an HP Microtower (HP DC5100M,P4-530). I've installed 2x 1gb DDR2 533mhz chips in the machine and the bios is only showing 1.536gb of RAM.
Each RAM module will show as 1gb in the bios if installed alone, but will only show up as 1.5gb if installed together. I have tried installing the RAM in slots 1&2 (shows as single channel) and then in 1&3 which shows as (asynchronous) in the bios.
I know I've come across this before, but I can't remember what the cause is. Is it because the motherboard needs a matched pair? I have 3 slots.