On: The Soul of an Old Machine

[sillywalk]

Inside the AS/400 by Frank Soltis, is a deep dive into IBM's AS/400 and its predecessor the System/38. Quite interesting. There is a 2nd or 3rd edition called Fortress Rochester: Inside the iSeries, but it tends to be hard to find and expensive.

[0] https://archive.org/details/insideas4000000solt/