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Originally posted by: Bossk
We've had this discussion before and the consensus decision was that Owen and Beru do remember 3PO and R2. But to further protect Luke, as was their charge, they disavowed any knowledge of their existence.
On the part of the droids, it was likely a memory wipe. Remember 3PO constantly rambling on in ANH about how R2 claims to have been the property of "a Captain Antilles"? Well, 3PO doesn't remember it. I say it's a memory wipe and it didn't completely take with R2.
Most likely Threepio was running on a typical unstable Microsoft operating system and his memory was wiped just about every time he so much as bumped into a wall. R2, on the other hand, was probably Linux which assured that most regular users wouldn't even know how to completely wipe his memory.