I wanted to max out my 20" G4 iMac with 2MB RAM. It had 1Gb stick in the inner (factory installed) location. Both MacTracker and EveryMac state, "Apple officially supports 1 GB of RAM in these models, but unofficially these models support 2 GB of RAM." So I added a 1GB SODIMM stick of PC2700 (200pin) into the user accessible location. Booted, but noticed it wasn't recognised. Re-installed it, same result. Inspected and cleaned the connector contacts with correct product spray can, and lightly cleaned the SODIMM stick contacts with a pencil eraser, reinstalled and booted. The result was the same, still only 1Gb recognised in the inner location. (See following screen shot). The following screen shots show the additional info given. The OS on this iMac is in French - but you get the gist. The first correctly details the 1Gb PC2700 184pin SDRAM stick at the inner location (DIMM1/J20). The second curiously shows the outer location (DIMM0/J22 as 'vide' (empty) although there is a 1Gb SODIMM PC2700 (200pin) stick installed. Thinking there may be incompatibility with different brands of memory, I then purchased further 1GB brand-new sticks from Amazon, both were 'Komputer Bay' manufacture (a brand I have purchased several times before, with never a problem). Installed both into the iMac. The results were identical to before. The inner 1GB memory is recognised, but not the outer 1Gb memory. Can anyone shed any light on this anomaly of non-identified RAM at the outer user accessible location? Is it possible that although not indicated, both memory sticks are in use? The machine is pretty damn quick, but there again it was even with only 1GB memory installed. My other 20" iMac is currently boxed and not immediately accessible, otherwise I would have already done a cross-check to understand further.