Kellyn Pot’vin-Gorman helps us understand where Oracle’s architecture differs from SQL Server’s:
The first thing you’ll notice is what Oracle refers to as an INSTANCE is different to what SQL Server calls one.
Oracle’s instance is most closely related to what SQL Server calls their database, (although it includes the files that Oracle includes in their description, too) and the Oracle home is *relatively* SQL Server’s version of an instance.
Read on for a deeper comparison from someone who has spent quite a bit of time working with both platforms.