I'm sure others here can come up with other examples?
IBM was kicking around emails on their SNA based VNET system in the mid-70s.
I dimly remember that if your "reader" (inbox) was too large, you needed to create a large temp disk, copy everything from your "A" disk to the temp disk, un-mount both, then mount the temp disk as your "A" disk, clean up your mail, then mount your "real" "A" disk as a temp disk, copy everything from the "temp" "A" disk to the "real" "A" disk, and then finally re-mount the "real" "A" disk ask the "A" disk, and then temp disk would be automatically deleted when you logged out.
Or something like that.
There will be a pop quiz about this later in the thread.
For my next act, I will show you how to enter CP, increase your virtual storage for the session, and then re-enter CMS with "i cms" . . .