With Microsoft® SQL Server™ 2000, you have the option of installing multiple copies, or instances of SQL Server on one computer. When setting up a new installation of SQL Server 2000 or maintaining an existing installation, you can specify it as:
- A default instance of SQL Server.
This instance is identified by the network name of the computer on which it is running. Applications using client software from earlier versions of SQL Server can connect to a default instance. SQL Server version 6.5 or SQL Server version 7.0 servers can operate as default instances. However, a computer can have only one version functioning as the default instance at a time.
- A named instance of SQL Server.
This instance is identified by the network name of the computer plus an instance name, in the format <computername>\<instancename>. Applications must use SQL Server 2000 client components to connect to a named instance. A computer can run any number of named instances of SQL Server concurrently. A named instance can run at the same time as an existing installation of SQL Server version 6.5 or SQL Server version 7.0. The instance name cannot exceed 16 characters.
A new instance name must begin with a letter, an ampersand (&), or an underscore (_), and can contain numbers, letters, or other characters. SQL Server sysnames and reserved names should not be used as instance names. For example, the term "default" should not be used as an instance name because it is a reserved name used by Setup.
Single and multiple instances of SQL Server 2000 (default or named) are available using the SQL Server 2000 Personal Edition, the SQL Server 2000 Standard Edition, or the SQL Server 2000 Enterprise Edition.
You cannot install a default instance of SQL Server 2000 on a computer that is also running SQL Server 7.0. You must either upgrade the SQL Server 7.0 installation to a default instance of SQL Server 2000, or keep the default instance of SQL Server 7.0 and install a named instance of SQL Server 2000.
You can install a default instance of SQL Server 2000 on a computer running SQL Server 6.5, but the SQL Server 6.5 installation and the default instance of SQL Server 2000 cannot be running at the same time. You must switch between the two using the SQL Server 2000 vswitch command prompt utility.
Multiple instances occur when you have more than one instance of SQL Server 2000 installed on one computer. Each instance operates independently from any other instance on the same computer, and applications can connect to any of the instances. The number of instances that can run on a single computer depends on resources available. The maximum number of instances supported in SQL Server 2000 is 16.
When you install SQL Server 2000 on a computer with no existing installations of SQL Server, Setup specifies the installation of a default instance. However, you can choose to install SQL Server 2000 as a named instance instead by clearing the Default option in the Instance Name dialog box.
A named instance of SQL Server 2000 can be installed at any time: before installing the default instance of SQL Server 2000, after installing the default instance of SQL Server 2000, or instead of installing the default instance of SQL Server 2000.
Each named instance is made up of a distinct set of services and can have completely different settings for collations and other options. The directory structure, registry structure, and service names all reflect the specific instance name you specify.