Understanding DBCC CHECKDB, Snapshots, and SQL Server Standard Edition
You can refer to Paul Randal's blog (the guy who wrote DBCC CHECKDB) :
CHECKDB From Every Angle: Complete description of all CHECKDB stages :

For SQL Server 2005, CHECKDB uses an internal database snapshot to provide the required transactional consistency.
So when CHECKDB starts in SQL Server 2005, the first thing it does is work out whether it can run online – if so it creates a hidden database snapshot of the source database (i.e. CHECKDB’s target database). As the database snapshot is hidden, there is no control over where the snapshot files are placed – in fact they are created as alternate streams of the files comprising the source database.
From SQL Server 2014 onward, alternate streams are not used, although the database snapshot is created in the same location as the existing database.

As a side note, since you are using Standard edition, DBCC CHECKDB will not perform parallel checking of objects as opposed to Enterprise edition wherein it honors the MAXDOP setting configured for the server instance.
Also, BOL has a clear writeup on CHECKDB Internal Database Snapshot