Curious as to where the A File is before it is sent to the DO

[guju]

I read that people see their thick A file during their interview at the DO. I am wondering where the file exists before it is sent to the DO. I had my one year temp work authorization was filled at TSC after graduating university. My H1, I140 and I485 was filled at NSC and my N400 is at NBC.
It doesn't matter, but I am interested to know who is responsible for compiling and maintaining every one's A file. Also what happens to the A file after the interview?
Any one has any ideas?
Thanks!

 

[Triple Citizen]

I believe there is a central storage facility in Lee's Summit, MO.

I am wondering where the file exists before it is sent to the DO.

 

[ginnu]

After you got I-485 approved and got GC files are sent to National storage at Lee's summit, MO. once you send N400 the file is requested from National storage with your Name, A# and sent to your Local USCIS where Interview will be conducted.
http://www.gao.gov/highlights/d0785high.pdf