Well... The Dell Studio 17 comes can support up to 4GB of Dual Channel 667MHz DDR2 SDRAM..
So, you need DDR2 SDRAM.
You should install memory in like pairs. Your computer has two banks, each with 2 sockets, so you should put 2GB in each socket for maximum performance.
I'm sure you COULD just install a 1GB in the second socket... but i'm not sure.
I recommend updating your BIOS before doing so, otherwise Windows might not recognize all of the memory (it'll recognize like 3.5GB) which would mean it wouldn't use ALL of the memory in it if it ever needed it.
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