When running Oracle databases on UNIX or Linux, it is easy to install a new Oracle Home without an outage. The work can be done during working hours, long before any change window or outage to existing databases and applications. The switch to a the new Oracle Home is also straight forward.
However, on Windows, there are a number of considerations for a cautious DBA, and a longer outage for upgrades may be unavoidable.
I’ve written some brief notes, based on my experience patching 126.96.36.199 to 188.8.131.52.21 on Windows Server 2008: Patching/Upgrading Oracle On Windows