Why only 16 registers in MVS?

[Dipak Dhoble]

It might sound too basic but I don't fnd a good explnation on this. The question is, why there is a constraint on the number of registers,16, in MVS?

[Robert Sample]

Because 16 is what the original S360 in 1964 came with. IBM has been very focused, over the years, on maintaining backward compatibility so programs that execute can continue to execute. IBM has extended the architecture over the years, but the basics have remained.

[prino]

Because 16 is what the original S360 in 1964 came with. IBM has been very focused, over the years, on maintaining backward compatibility so programs that execute can continue to execute. IBM has extended the architecture over the years, but the basics have remained.

Actually, since the introduction of the instructions that use the high part of registers, it is now possible to have, in essence, 32 registers. Enterprise PL/I already uses it for the last few versions.