Mainframes are interesting to me (but I think a lot of things are interesting) :)

I found this one site with links to books on mainframes: http://www.mainframes.com/Books.html

If IBM is investing in 14nm tech for mainframes, it's not dead tech. A quick search revealed the following:

""" 70% of the world's production data, and 55% of world's enterprise transactions, took place on mainframes (2016) """

http://ibmmainframes.com/wiki/who-uses-mainframes.html