Your USN is the unique student number that was allocated to you when you were a student at the University of Cambridge - this is a nine digit number which can be found on copies of academic transcripts, verification documents or correspondence you may have retained from the admissions office confirming your place at Cambridge
A Common Registration Scheme Identifier (CRSid) is the name of the identifier given to anyone who needs to access IT resources at Cambridge. It's made up of letters and numbers – for example, acb123. The letters of a CRSid may match some of the initials in the owner's name, there is no formal association between the letters in a CRSid and the owner's name.
If you require assistance retrieving either USN or CRSid, please contact the Student Registry, ensuring that you provide your full names, date of birth, College, subject. You can submit your request online here.