Memory drain from 4 GB down to 2.6 GB before I even start

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I just upgraded a DELL to 4 GB of memory. I only get 3.24 GB reported in the Computer>Properties window and DELL then reports, with their utility, that only 2.6 GB is available. Goodness what I drop from 4 GB!!! I begin to understand why the drop to 3.2 but where is the next 600 MB going on this DELL Inspiron 530?
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