See this link for an idea:
The IBM iSeries mid-range computing platform is a highly available system running the proprietary OS/400. The processor is a 64-bit PowerPC RISC processor. This system has been doing 64 bit since the mid-'90s (it was 48-bit prior to that, since the '70s). All the hardware on this thing is proprietary but industrial strength. Disks are of the DASD variety.
Isn't this the latest version of the architecture originally introduced by IBM (InternationalBusinessMachines) General Products Division in Rochester (MN, USA) as the System/38?
Yes, system/36 & 38 were the predecessors to the iSeries(AS/400).
Ahh, yes -- the wonderful System/36-8. A totally locked up OS running on a uniquely pigeonholed architecture. No support in the third party market of any real depth, and even the IBM business partners avoided the things. Want to get shoved into a dark corner with no future? Then buy one of these beaters.
See: IseriesArchitectureCategoryHardware, CategoryComputerCompany, CategoryComputerArchitecture