One of the more unique aspects of the AS/400 is the single level store. I haven't ever used it, but the general idea is that it does away with the file system in exchange for a single, flat address space. This simplifies the programming model.
The AS/400 also runs something like bytecode, rather than directly on the hardware. This has given IBM the flexibility to change the underlying architecture in fairly radical ways. (new CPU ISAs, etc.)
Historically, the AS/400 has some significance to IBM beyond the fact that it's been a commercial success. After IBM did so well with the System/360, they started work on the next big thing: IBM Future System. The idea was that FS was something only IBM could do, because only IBM had the research budget and staff to pull it off. As these things often go, FS didn't achieve its grander goals, but it did spin off several technologies that IBM did commercialize. In addition to several System/370 processors, the Future System work also ultimately resulted in the AS/400.
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.
"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.
http://en.wikipedia.org/wiki/Single-level_store
The AS/400 also runs something like bytecode, rather than directly on the hardware. This has given IBM the flexibility to change the underlying architecture in fairly radical ways. (new CPU ISAs, etc.)
Historically, the AS/400 has some significance to IBM beyond the fact that it's been a commercial success. After IBM did so well with the System/360, they started work on the next big thing: IBM Future System. The idea was that FS was something only IBM could do, because only IBM had the research budget and staff to pull it off. As these things often go, FS didn't achieve its grander goals, but it did spin off several technologies that IBM did commercialize. In addition to several System/370 processors, the Future System work also ultimately resulted in the AS/400.