Where should the type information be 128

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But a true stack machine doesn't have registers (as Peter points out - at least from a programmer's point of view) at all and uses the stack for EVERYTHING, not just preserving info across call boundaries. Perhaps some illustrative code might make things clearer.

HLL code A = (B * C) + (D + E)

Traditional register code

Load Register 1, B Load Register 2, C Multiply Register 3, Register1, Register2 Load Register 1, D Load Register 2, E Multiply Register4, Register1, Register2 Add Register 3, Register3, Register4 Store Register3,A

Stack oriented code

Push B Push C Multiply Push D Push E Multiply Add Pop A

Note that in the stack code, there are NO register numbers. All calculations are done on the stack. This has advantages and disadvantages. BTW, the maximum stack depth for this code is three.

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Yes. That is the traditional way of handling stacks on a register machine. On a stack machine, the stack is the primary thing and there are no registers to "go through". All things, even those that you did in registers - such as arithmetic - are done on the stack using stack oriented instructions.

Thank you.

Yup. Precisely!

But wouldn't PDP-10 code look closer to the first fragment I wrote above than the second? You could compute the results of the statement I used to illustrate the difference directly on your HP calculator. In fact, the key strokes would be pretty much as I wrote - just subsbreastute "enter" for "push". But you could't do that on a "traditional" calculator unless you either had a place ("a memory " AKA register) to store the results of the first multiply, or had a calculator that supported parentheses ( which make use of the memory behind your back).

You don't need to put the whole array onto the stack at once. Only the elements on which you are operating at the moment. In practice, a depth of a handfull is sufficient for most applications. You could always pop to memory as "scratch" storage.

-- - Stephen Fuld e-mail address disguised to prevent spam