What is rowversion in SQL Server?

The SQL Server rowversion data type (aka, timestamp) is basically a database-wide Autonumber field.

Any time a record in a table with a rowversion column is added or updated, the global rowversion counter is incremented at the database level and the new value is assigned to the added/updated record.  It's an easy way to see if a record has changed without checking each field.

I recommend adding a rowversion field to every SQL Server table you link to from MS Access as it boosts performance, helps avoid weird bugs, and has no real downsides.