How to create instance in SQL Server 2008

I have SQL Server 2005 Express installed. Later I upgraded to SQL Server 2008. I don't know much about instances, but when I log into SQL Server 2005 and I开发者_C百科 log into SQL Server 2008 it is showing the same number of databases. Also, when I create a database in SQL Server 2008 it is showing it in SQL Server 2005.

Any Idea how can I create a separate SQL Server 2008 instance?

If possible please explain step by step.

Thanks

An instance of a SQL Server database is just a named installation of SQL Server. The first one you install on any given machine typically is the default instance, which has no specific name - you just connect to it using the (local) name or the name of the server machine.

SQL Server Express typically installs as a SQLExpress instance - so the instance is called SQLExpress, and you connect to it using (local)\SQLExpress or .\SQLExpress or MyServerMachine\SQLExpress.

SQL Server instances are totally independent of one another, and you can basically install as many as you like - you just have to make sure to use unique instance names for each. But when you run the SQL Server Installation again, it will show you what instances are already installed, and prompt you for a new instance name for a new installation. No harm done.

Run the install program again, and when prompted whether you want a default or a named instance, specify a named instance with a different name. A default instance make looks like this:

servername

A named instance looks like this:

servername\instancename

"you can basically install as many as you like"

There are limitations, like 50 in 2008.

http://technet.microsoft.com/en-us/library/aa174516(v=sql.80).aspx Microsoft does not support more than 16 instances on a single computer or failover cluster.

There are a few more limitations.