IMAC DUO accepts 2GB memory in top slot, not bottom

I've got a 1.83 GHZ Intel Cor 2 Duo that came with 2 256 MB 667 MHZ SDRAM memory units. I bought 2 Axiom 2 GB 667 MHZ SDRAM units. Both work in the top slot with the original 256 MB chip installed. Neither works in the bottom slot, either with the other 2 GB unit in the top slot, or the original 256 MB unit. Has anyone else had a similar problem? Thanks

Macs tend to be picky about memory. I would recommend you purchase memory modules from a well-known and established vendor like Crucial.com or OtherWorldComputing.com.

Are you sure this iMac is a Core 2 Duo and not a Core Duo? I don't remember any Core2Duo Macs that came with a 256Meg module.

To the OP:

The machine is probably limited to 2 GB of memory. As dtravis7 stated, your machine is more than likely a Core Duo. If that's true, the memory slots would have been populated with 2 x 256 MB modules for a total of 512 MB.

The 2 GB limit means you can either put 2 x 1 GB modules in both slots, or 1 x 2GB module in the first or top slot. Total memory in either case = 2 GB. For maximum efficiency and speed you should use 2 x 1 GB modules.

Regards.

Is Intel Core 2 duo

"About this mac" in the apple menu says Intel Core 2 duo. With one 2 GB module and one 256 MB module installed, the memory is listed as 2.25 GB, so it has to be able to accept more than 2 GB total memory. If the mac is picky about memory, than why should it accept a 2 GB module in one slot and reject the same module in the other?

While the machine will recognize what hardware you have, it is only capable of utilizing 2 GB. This is a limitation of the hardware in the machine.

I have 4 GB installed in my MBP while the hardware is only capable of using up to 3 GB. About this Mac reports that I have 2 x 1 GB sticks installed, however, the machine can only address 3 GB worth of it.