In this section you learn about the different types of installations: side by side, upgrade, and new. Details about upgrades are covered in Chapter 3. You can also create a script that installs SQL Server for you. This can be very useful when you need to complete many similar installations.
Each install works with a single instance. If you wish to install a named instance of the Database Engine and a default instance of Analysis Services, you must go through two separate install processes.
A new install occurs when no other SQL Server components are on the server and you have a clean slate to work with. Make sure that there are no remnants of previous SQL installs. Check the directories and the registry to ensure that you have a clean system.
If SQL Server components exist on the box, you can upgrade the existing instance. In this case, you install SQL Server on top of the existing instance. SQL Server also supports a side-by-side install. A side-by-side install occurs when you are adding another instance of SQL Server. SQL Server 2008 supports multiple instances of the Database Engine, Reporting Services, and Analysis Services on the same box. It will also run side by side with previous versions of SQL Server. If the existing instance is a default instance, of course, your new install must be a named instance. The following table indicates which versions can run side by side with SQL 2008.