AS/400 descended from S/38, but is not the same. In particular the System/38 architecture had capability-based addressing¹ — essentially, you can perform a particular kind of access if and only if your pointer contains the necessary permission.

¹Levy, Henry M. (1984). Capability-based computer systems. http://homes.cs.washington.edu/~levy/capabook/index.html Chapter 8 covers the IBM System/38.

"in June 1988, IBM announced the results of Silverlake as the Application System/400, or AS/400. In many ways, the box was a repackaging of the System/38, with some left over Fort Knox parts,"

Brian Kelly was an IBM Midrange Systems Engineer for 30 years, and has spent nearly a decade as a System i5 consultant based in Scranton, Pennsylvania. He is also author of thirty AS/400, iSeries, and System i5 books and he serves as an assistant professor at Marywood University, which uses the OS/400 and i5/OS platform and teaches courses in the box as well. http://www.itjungle.com/tfh/tfh040708-story05.html

My point was that the S/38 used some of the detritus from Fort Knox not, directly, the AS/400.

Quite a lot of work went into the AS/400 so it wasn't just a renamed S/38, but any discussion of the AS/400 should recognize its origins.