Now although when you install SQL Server, you don't get any of the sample databases like AdventureWorks, what you will see, if you're looking through SQL Server Management Studio, is you will see at least four system databases. Four is pretty typical for a right- out-of-the-box standard installation. You have got master, model, msdb, and tempdb and I'm often ask how important are these and are you supposed to do anything with them, are you supposed to change them? Well in this particular course, we're unlikely to touch any of them at all.
You are just going to leave them alone but to give you the quick runthrough of what they mean, yes, they are important, they are vital. The master database, which even sounds important straight off the bat, is the one database that says what exists in this instance of SQL Server. If the master database wasn't available, the instance doesn't even start. It won't run. This says what else is available. The model database can be changed but you're unlikely to at this level of content.
What model does is it describes the template for a new database. So later on in this course, when we make a new database, it will actually be based on model. So say at some point in the future, you had a very specific database creation process. You might change model so that every new database was based on your changed design. msdb is used internally and it's used for queuing and to put some jobs to have things run in the background such as database mail and a little part of SQL Server called Service Broker.
We won't really be touching either of these in this course. The only other one we have here is tempdb. Again, you might look at the name and think it looks like it's something temporary and it is. This is really a scratchpad for SQL Server. tempdb is used when SQL Server is doing large amounts of calculation and sorting and it's reordering things. It uses that as kind of scrap paper to write things on. If you were to shut down and restart SQL Server, you'd find a tempdb would be deleted and re-created.
So that's the basic idea of what these four databases are for. In this course, we won't be touching them, but if you're curious about them, they are vital. just leave them alone.
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