You can install SQL Server 2005 on a computer already running instances of a previous SQL Server version. If a default instance already exists on the computer, SQL Server 2005 will be installed as a named instance.

Important   For SQL Server 2005 installations in side-by-side configurations with previous versions of SQL Server, SQL Server 2005 services must use accounts found only in the global domains group. Additionally, accounts utlized by SQL Server 2005 services must not appear in the local Administrators group. Failure to comply with this guideline will result in unexpected security behavior.

Side-by-side support is as follows:

Side-by-side support	SQL Server 2000 (32-bit)	SQL Server 2000 (64-bit)	SQL Server 2005 (32-bit)	SQL Server 2005 (64-bit) IA64	SQL Server 2005 (64-bit) X64
SQL Server 7.0	Yes	No	Yes	No	No
SQL Server 2000 (32-bit)	Yes	No	Yes	No1	Yes
SQL Server 2000 (64-bit)	No	Yes	No	Yes	No
SQL Server 2005 (32-bit)	Yes	No	Yes	No	Yes
SQL Server 2005 (64-bit) IA64	No	Yes	No	Yes	No
SQL Server 2005 (64-bit) X64	Yes	No	Yes	No	Yes

¹The 32-bit editions of SQL Server are supported in WOW64 only on the X64 versions of 64-bit operating systems. The 32-bit editions of SQL Server are not supported in WOW64 on the IA64 versions of 64-bit operating systems.

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