SQL Server- Limit to Concurrent table queries?
How is it that N number of users can access the same physical data at the same time?


This is done using transactions (honors ACID properties) &amp; concurrency models. SQL server supports Optimistic concurrency as well as Pessimistic concurrency (default concurrency model) which inturn uses different isolation levels (read committed is the default isolation level ) and locking mechanism to allow multiple users access the data at the same time.

Refer to : SQL Server Transaction Locking and Row Versioning Guide