Where does the PS3 store user accounts

I ask the question because i recently had to send my PS3 back to get repaired/replaced but I had put a 320GB Hard drive in it, in case it was replaced I didn't want to lose that HD but I'd lost my original 60GB HD so I bought I cheap replacement to put in the PS3 before sending back.

When my PS3 came back repaired I booted it and all 4 user accounts from my PS3 were on the system but I had assumed these would be on the HD i'd taken out.

Solution 1:

User accounts, PSN account info and updates are not stored on the hard drive, but on the PS3's internal flash memory. Media, game saves, downloaded content etc. is stored on the hard drive.