Starting with SQL Server 2005 you can create, rebuild, or drop indexes while concurrent users read or modify the underlying table or clustered index data and any associated nonclustered indexes during these index operations. This mode of performing index operations is known as online.
To be able to use online index operations and therefore provide higher system concurrency and better scalability, especially while index maintenance occurs, you must be running the Enterprise edition (or a Developer Edition or an Evaluation Edition, both of which behave exactly like the Enterprise does. The only difference among them three is their licensing.)
Any attempt to run an index operation statement with the ONLINE enabling clause in a non-Enterprise will raise error 1712 “Online index operations can only be performed in Enterprise edition of SQL Server.”
This post is part of the a series I decided to call “Understanding the value of the Enterprise Edition, one feature at a time” which I started in September 2011 and will grow on a weekly basis, having a new post incorporated to the family every Friday.