Go to Settings → System Settings → System Information . It should read “System Software: Version 6.60”.
They called the upgrade "660" because people like neat numbers. In truth it was a set of wishes: cleaner clock, sharper textures, a softer hum when the UMD cradle closed. M33 had stitched itself to firmware like a seamstress to a coat — clever shortcuts, borrowed gestures from brighter devices, an empathy for games that wanted to run without asking for permission.
: If you receive a "DRNFFFFFFCD" or "dadada" error, you likely have corrupted "keys." Use a tool like Chilly Willy's Key Cleaner to fix your IDStorage before trying the update again. PSP: Updating from the 3.xx OE CFWs to the 6.60 ME CFW 5 Sept 2013 —