Think of them as say, your AWS. Except that you can just start randomly replacing hardware without the software skipping a beat. That’s the level of redundancy and stability these things offer.
I didn’t know this either until I started just researching a while back. It’s amazing. They get a bad rep, but they are very very awesome and modern.
As a rule of thumb, if there's something in computing you've heard about, expect IBM to also have heard about it and made something like it for their machines. Sometimes they lag a bit but eventually they converge towards having their own of all things computational.
I didn’t know this either until I started just researching a while back. It’s amazing. They get a bad rep, but they are very very awesome and modern.