Inside GL Year End

Hi,

During year end we know that Balance sheet accounts are  carried forward and Retained earning is populated based on P&L accounts.

Suppose

Revenue 100

Expense 50

Retained earning account is credited with 50.

Now how does this actually happens in GL.

1)Does the system create a new journal to credit the Retained earning account as soon as we open the new period?

2)Is is a direct update in the system to the GL balances table and no journal is created?

Basically what exactly happens in system(which concurrent programs,data base updates) as soon as we open a new year.

Thanks