You may install multiple instances (or copies) of Microsoft SQL Server 2005 on the same computer. This is applicable to installing alongside different editions as well as earlier versions Microsoft SQL Server. In other words, you can have more than one set of Microsoft SQL Server installed on one machine working independent from one another.
This capability enables us to strategize the utilization of hardware resources to achieve our needs. It allows test for different customer utilizing different SQL Server edition and version on one server. It is also useful when you host database for customers that requires full administrative control of their SQL Server instance.
Default Instance and Named Instance
There are two types of installation allowed for SQL Server installation; default instance and named instance.
The default instance is an installation where you do not give a name to the instance of Microsoft SQL Server. In this case, the instance name will take the name of the server. Hence, you refer to the Microsoft SQL Server by specifying the server name. Due to the use of server name as instance name, you are only allowed to install one default instance on one machine.
A named instance is an installation where you have to specify a name for the instance of Microsoft SQL Server during installation. The instance of Microsoft SQL Server will be referred in the form of [SERVER NAME]\[INSTANCE NAME]. You may install more than one named instance provided the name of each instances are different.
When you start Microsoft SQL Server installation wizard, it detects whether the default instance already exists. If it could not find one, you will be given the option to install a default instance or a named instance. Otherwise, you will only be allowed the option of installing a named instance.
The following figure shows the screen where you choose the type of instance to be installed. It is part of the installation process.
Conclusion
This capability leaves rooms to creatively strategize installations of Microsoft SQL Server to our needs. However, we have to be wary of the administration overhead and the duplication of components. Each instance will take up additional hard disk space, memory utilization and processor capacity.
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