Where should the type information be 125

And FWIW the original Tandem (later Compaq and HP) NonStop CPU, actually built (in mildly modified form) until IIRC 1992 and still supported in emulation, is a hybrid of stack (like Burroughs or HP3k) and register machine.

There are (exactly) 8 16-bit 'normal' registers plus a 3-bit pointer, and most 'vanilla' instructions use these in a stack fashion: LOAD is to R++RP, SUB of RRP from R--RP, etc. 8 is just enough for the two operands of a 64-bit integer or 64-bit floating operation, and beyond 8 (or less) 'you' (usually the compiler) can explicitly spill to and refill from the memory stack, which is also used for locals and call-return. (By 'normal' I exclude dedicated and unaddressable regs like Program counter, Stack pointer, etc.)

By compiler and OS convention, procedure (and subprocedure to one level only!) arguments are always spilled before call, but in hand userland buttembler you can use the registers, and the compiler(s) do so for some internal stuff like out-of-line prologues.

R5 R6 and R7 can also be used as indexes on (most) memory reference, and directly addressed by instructions intended for indexing but also usable for simple 16-bit arithmetic: load or add-subtract small constant, add-subtract to-from registers stack, and one special branch Of course while using R5-7 this way you can't use the full 8 register stack, and thus not quadword operations, unless you (again, the compiler) spill-reload incessantly.

TNS, actually its successive versions, also have rather unusual memory model(s), not to mention system (as opposed to CPU) architecture for fault tolerance, but those are essentially unrelated issues.

- David.Thompson1 at worldnet.att.net