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Instance Name

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SQL Server Express users: click Instance Name (SQL Server Express) for information that is specific to SQL Server Express Setup.

Use the Instance Name page of the SQL Server Installation Wizard to specify whether to create a default instance or a named instance of SQL Server. A default instance name is used unless you choose a named instance.

Each SQL Server instance is made up of a distinct set of services with specific settings for collations and other options. The directory structure, registry structure, and service names all reflect the specific instance ID of the SQL Server instance created during SQL Server Setup.

An instance is either the default instance or a named instance. The default instance name is MSSQLSERVER; it does not require a client to specify the name of the instance to make a connection. A named instance is determined by the user during Setup.

A named instance can be installed at any time. By default, the first time you install SQL Server 2005 on a computer, Setup specifies the installation as the default instance; however, you can choose to install SQL Server as a named instance without installing the default instance first. The default instance could be an installation of SQL Server version 6.5, 7.0, 2000, or 2005. Only one installation of SQL Server, regardless of version, can be the default instance at any one time.

Multiple Instances

SQL Server 2005 supports multiple SQL Server instances on a single server or processor, but only one instance can be the default instance; all others must be named instances. A computer can run multiple instances of SQL Server concurrently, and each instance runs independently of other instances. All instances on a single server or processor must be the same localized version of SQL Server 2005.

The following table shows the number of instances supported for each instance-aware component in the different editions of SQL Server 2005.

SQL Server 2005 edition Database Engine instances Analysis Services instances Reporting Services instances

Enterprise Edition

Developer Edition

50

50

50

Standard Edition

Workgroup Edition

Express Edition

16

16

16

Options

If you select Default instance and a default instance already exists on the computer, SQL Server Setup will upgrade the default instance. If you enter the name of a named instance that already exists on the computer, SQL Server Setup will upgrade the named instance.

All components of a given SQL Server 2005 instance are managed as a unit; all SQL Server service packs and upgrades will apply to every component of a SQL Server instance.

Consider the following information when deciding whether to install a default or named instance of SQL Server 2005:

  • If you are upgrading from SQL Server version 7.0, the upgraded instance is a default instance.
  • If you plan to install a single instance of SQL Server on a database server, it should be a default instance.
  • If you must support client connections from SQL Server version 7.0 or earlier, it is easier to use a default instance. Although older clients can be configured to connect to a named instance, each client requires a "server name" definition and a hard-coded network address for the named instance.
  • Consider a named instance for situations where you plan to have multiple instances on the same computer, as a server can host only one default instance.
  • Any application that installs SQL Server Express Edition should install it as a named instance. Doing so minimizes conflict in situations where multiple applications are installed on the same computer.

  • Default instance
    Choose this option to install a default instance of SQL Server 2005. A computer can host only one default instance; all other instances must be named. However, if you have a default instance of SQL Server installed, you can add a default instance of Analysis Services to the same computer.

    To upgrade the default instance of a previous SQL Server installation, click the Default Instance radio button and then click Next.

  • Named instance
    Choose this option to create a new named instance. Bear in mind the following when naming an instance of SQL Server:

    • Instance names are not case sensitive.

    • Instance names cannot contain the terms "Default," "MSSQLServer," or other reserved keywords. If a reserved keyword is used in an instance name, a Setup error will occur.

    • Instance names are limited to 16 characters.

    • The first character in the instance name must be a letter or an underscore (_). Acceptable letters are those defined by the Unicode Standard 2.0, including Latin characters a-z, A-Z, and letter characters from other languages.

    • Subsequent characters can be letters defined by the Unicode Standard 2.0, decimal numbers from Basic Latin or other national scripts, the dollar sign ($), or an underscore (_).

    • Embedded spaces or other special characters are not allowed in instance names; nor are the backslash (\), comma (,), colon (:), semi-colon (;), single quote ('), ampersand (&), or at sign (@).

      Note

      Only characters that are valid in the current Microsoft Windows code page can be used in SQL Server instance names. If an unsupported Unicode character is used, a Setup error will occur.

  • Installed instances
    View a list of installed SQL Server instances and components on the computer where SQL Server Setup is running. The installed instance details pane will display upgrade options for installed instances.

Note that all components of SQL Server that share the same instance name must meet the following criteria:

  • Same version. For example, you cannot install an instance of SQL Server 2005 Analysis Services (SSAS) with the same instance name as SQL Server 2000 Database Engine on a single computer. In addition, when you upgrade one component with a given instance name to a new version or service pack, you must upgrade all components of that instance.

  • Same edition. For example, you cannot install an instance of SQL Server 2005 Integration Services (SSIS) Evaluation Edition with the same instance name as SQL Server 2005 Database Engine Enterprise Edition on a single computer.

  • Same language. For example, you cannot install an instance of German SQL Server 2005 Database Engine with the same instance name as Portuguese (Brazil) SQL Server Management Studio on the same computer.

  • Same clustered state. For example, you cannot install a clustered instance of SQL Server 2005 Analysis Services (SSAS) with the same instance name as a nonclustered instance of SQL Server 2005 Database Engine on the same computer.

    Note

    Reporting Services is not cluster-aware.

  • Same platform. For example, you can not install an instance of Business Intelligence Development Studio (32-bit) with the same instance name as an instance of SQL Server 2005 Database Engine (64-bit).

See Also

Other Resources

Database Engine Installation How-to Topics

Help and Information

Getting SQL Server 2005 Assistance