I have a better link. Scroll down to the end, and click on "Redbooks"; there you'll find the technical information we HN readers tend to be more interested in.
In particular this one: "IBM z14 Technical Introduction" https://www.redbooks.ibm.com/redbooks/pdfs/sg248450.pdf (I'm still reading it, but page 5 already has a short list with "the main technical enhancements in the z14 over its predecessor platforms").