The 5100 / 5110 used two emulation layers, one for the S/360 architecture, used to tun APL 360, and a S/3 emulation used to run BASIC. Amazingly, these emulation characteristics weren't disclosed in the manuals.

Don't miss to google "John Titor" in this context ...

[Edit] Some links:

1) The sections on SCAMP (the prototype forerunner of the IBM 5100) and on Small Machines in "The IBM family of APL systems" by A.D. Falkoff: https://web.archive.org/web/20071031134817/http://www.resear...

2) On PALM and 32-bit microcode this talk at Wikipedia: 3) https://en.wikipedia.org/wiki/Talk%3AIBM_5100

3) On the John Titor story: https://groups.google.com/forum/#!topic/alt.folklore.compute...