They are built and sold in the similar sense as above mentioned AS/400 is built and sold. The user-visible CPU architecture is from the start designed as VM abs

They are built and sold in the similar sense as above mentioned AS/400 is built and sold. The user-visible CPU architecture is from the start designed as VM abstraction provided by the OS, which itself runs on real hardware that does not necessarily use same instruction set. Thus the today's hardware is something essentially off-the shelf (x86 in the unisys case, power for as/400). On the other hand S/360 ("the mainframe") compatible hardware is still being manufactured by IBM and AFAIK even Fujitsu (which in addition to being S/360-compatible mainframe supplier themselves also bough Amdahl, which was the original IBM-compatible mainframe manufacturer, with the company/founder name saying a lot ;)).