There are three different Db2 databases.

I believe the mainframe version was first.

There is a version baked into the os/400 operating system (i series).

Then unix/windows Db2 came last, if memory serves.

https://en.wikipedia.org/wiki/IBM_Db2

It's very amusing to me that you bring up IBM in a discussion of the value of Oracle.

I came here to say that if you want to understand Oracle's value, think IBM with less history.