> OS/400 -- now called IBM i -- sounds like it was ahead of its time:

That's because it's the last remnant of Atlantis.

https://people.cs.clemson.edu/~mark/fs.html

> The IBM Future System (FS) project was a design effort to succeed the IBM S/370 architecture that was adopted company wide in 1971. FS was based on a single-level store with automatic data management. The project is reputed to have cost more than $1B when it was cancelled in February 1975, but the single-level store idea was adopted by System/38, AS/400, and iSeries.

Single-level store is IBM's cutesy way of saying that there's no application-level distinction between disk and RAM: It's all data, applications access data (or don't, depending on a security model), and the OS handles persistence the same way it handles caching; that is, transparently.

Anyway, security was important to IBM, particularly the security to be free from people making clones of FS hardware. This had unfortunate effects on the systems's comprehensibility:

http://www.cap-lore.com/CapTheory/KK/FS.html

> Some suggest that this memo[0] was the beginning of the end of IBM’s Future System. The section of the memo with “security” in the heading, concerns keeping the architecture secret, from most of those working on the project. Quote:

>> Tight security prevents a potential thief from stealing a system design. But good communication is necessary to design a system that is worth stealing. The recent version of the RIPON architecture has been issued in 15 separate, registered confidential documents. A programmer who gets authorization to learn about the addressing structure has to demonstrate a separate need to know to learn the instruction set. The avowed aim of all this red tape is to prevent anyone from understanding the whole system; this goal has certainly been achieved.

[0] http://www.jfsowa.com/computer/memo125.htm

It evolved:

http://www.jfsowa.com/computer/

> In 1978, a scaled-down version of FS was announced as System/38. The greatest strength of HLS, AFS, and System/38 was a “one-level store”: a virtual memory that eliminated the distinction between RAM and files on disk drives. That made System/38 much easier to program than earlier computer systems or even most systems today. But the instruction set of System/38 was essentially System/370 with descriptors. The microcode of any 370 system could have been modified to support it, and programming for FS could have begun in 1971.

> As another option, John Cocke had designed a RISC machine, which eventually became the Power PC. In 1994, under the name AS/400, it ran a later version of the System/38 software. But as early as 1971, Cocke had persuaded the AFS group that a conventional computer with the HLS descriptors and a well-designed compiler could run the FS software. That computer could be a modified System/370, his RISC design, or both. The first FS machine could have been delivered as an “option” of the IBM 3033, which was announced in 1977 and delivered in 1978.

> An even better option was a high-speed System/370-compatible machine that Gene Amdahl had designed in 1969. Unfortunately, that project was canceled for political reasons. Therefore, Amdahl left IBM, got funding from Fujitsu, founded the Amdahl Corporation, and delivered his 470 system in 1975. Until the IBM 3033 in 1978, Amdahl’s machine was much faster than anything IBM was selling. With suitable microcode, a design by Cocke or Amdahl could have served as the high-end hardware for FS. System/38 would have been the entry-level version for smaller systems.