What is the Difference Between Default Instance and Named Instance in SQL Server? with Proper Definition and Brief Explanation

The main difference between them is that a SQL server can only have one default instance but it can have multiple named instances. 

SQL Server is an RDBMS from Microsoft. It allows users to create databases and organize data in database tables. The user can manipulate the data using the structured query language. The SQL instance is a copy of the executable file sqlserver.exe. It is a SQL server installation. There are two types of SQL server instances as default instance and named instance. When installing SQL server, the instance configuration window appears and the user can specify whether to create a default instance or a named instance.

Key Areas Covered

1. What is the default instance?
     – Definition, Functionality
2. What is called an instance?
     – Definition, Functionality
3. What is the difference between them?
     – Comparison of key differences

Key terms

Default Instance, Named Instance, SQL Server

What is the default instance?

If a SQL server is not already installed, a default instance will be created unless the user specifies a named instance. There can only be one default instance. The default instance name is MSSQLSERVER. For example, suppose a Java or .NET application program sends data to a database in the default instance. It does not require the client to specify the instance name to make the connection. When there is a default instance of SQL server installed, the user can add a default instance of analytics services to the same machine.

What is a named instance?

The named instances are all instances other than the default instance. When the programmer gives the instance a name when installing it, it is a named instance. In other words, the user determines a named instance during configuration. Also, it is possible to install SQL Server as a named instance without first installing the default instance.

                                                                 Figure 1: SQLServer

However, there are certain rules to keep in mind when creating a named instance. Instance names are not case sensitive. Also, they cannot begin or end with an underscore (_). The user may also not use “Default” or other reserved keywords to name the instance. If you use a reserved keyword, SQL server will show a configuration error. Also, the first character must start with a letter, while the maximum number of characters in the instance is 16. Also, it is not possible to use spaces or special characters like black slash, colon, comma, single quote, hyphen, etc. . in the instance name.

Difference between default instance and named instance


A default instance is an instance type that is used when installing a single instance of SQL server. In contrast, a named instance is an instance type where the user specifies an instance name when installing the instance.


There is only one default instance, but you can have multiple named instances. So this is the main difference between them.


If the user plans to install a single instance of SQL Server, it is a default instance. However, if the user plans to install multiple instances on the same machine, then the instances other than the default instance are called instances. So, this is another difference between them.


Default instance and named instance are two types of SQL server instances. The main difference between them is that there can be only one default instance in SQL Server while there can be multiple named instances in SQL server.


1.”Database Engine Instances (SQL Server).” Microsoft documents, available here.
2. “Instance configuration”. Microsoft Docs, available here.

Courtesy image:

1. “SQL Server” By Soumyasch – Own work (CC BY-SA 3.0) via Commons Wikimedia

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