My assumption would be that after the syntax of the DML statement was validated the appropriate rows (based on the where clause) are loaded into memory with these rows being marked so that they're locked from others updating them. The appropriate redo & undo change vectors are generated (does somebody know by what process?) related to this update; the redo & undo being written to the TLog by lazywriter and the undo record is logged in the tempdp. Then the operations are applied in memory and, assuming the update wasnt in a still running transaction then the update is commited & others can see it. Row level locks are removed & the tempdb record is marked as being no longer needed (due to the commit).

Or something is wrong here?

Dird