HP memory - not fitting? (PC-5300F vs PC-5300P)

We have a server that's running HP PC2-5300F-555-11-B0 memory.  I purchased HP PC2-5300P-555-12-ZZ memory, and it doesn't fit... (the slot in the RAM doesn't match up).  

Not sure what the difference is... looks like one is "555-11" and one is "555-12", plus one is 5300P and the other 5300F.

Any idea?
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PC2-5300F has fully buffered modules -- "server grade" RAM, also known as FB DIMMs.

As you have noticed, the notches do not line up, as they are unique to fully buffered modules.  Therefore you can only put FB DIMMs into those slots.

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Mystical_IceAuthor Commented:
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