Re: [COFF] Compilation "vs" byte-code interpretation, was Re: Looking back to 1981 - what pascal was popular on what unix?

Re: [COFF] Compilation "vs" byte-code interpretation, was Re: Looking back to 1981 - what pascal was popular on what unix?

[Peter Jeremy via COFF]

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=> COFF

On 2022-Jan-30 10:07:15 -0800, Dan Stromberg <drsalists@gmail.com> wrote:
>On Sun, Jan 30, 2022 at 8:58 AM David Barto <david@kdbarto.org> wrote:
>
>> Yes, the UCSD P-code interpreter was ported to 4.1 BSD on the VAX and it
>> ran natively there. I used it on sdcsvax in my senior year (1980).
>
>This reminds me of a question I've had percolating in the back of my mind.
>
>Was USCD Pascal "compiled" or "interpreted" or both?
>
>And is Java?  They both have a byte code interpreter.

A bit late to the party but my 2¢:

I think it's fairly clear that both UCSD Pascal and Java are compiled
- to binary machine code for a p-code machine or JVM respectively.
That's no different to compiling (eg) C to PDP-11 or amd64 binary
machine code.

As for how the machine code is executed:
* p-code was typically interpreted but (as mentioned elsewhere) there
  were a number of hardware implementions.
* Java bytecode is often executed using a mixture of interpretation
  and (JIT) compilation to the host's machine code.  Again there are
  a number of hardware implementations.

And looking the other way, all (AFAIK) PDP-11's were microcoded,
therefore you could equally well say that PDP-11 machine code is being
interpreted by the microcode on a "real" PDP-11.  And, nowadays,
PDP-11 machine code is probably more commonly interpreted using
something like simh than being run on a hardware PDP-11.

Typical amd64 implementations are murkier - with machine code being
further converted ("compiled"?) into a variable number of micro-ops
that have their own caches and are then executed on the actual CPU.  
(And, going back in time, the Transmeta Crusoe explicity did JIT
conversion from iA32 machine code to its own proprietary machine code).

-- 
Peter Jeremy

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Re: [COFF] Compilation "vs" byte-code interpretation, was Re: Looking back to 1981 - what pascal was popular on what unix?

[Noel Chiappa]

    > From: Peter Jeremy

    > all (AFAIK) PDP-11's were microcoded

Not the -11/20; it pre-dated the fast, cheap ROMs needed to go the micocode
route, so it used a state machine. All the others were, though (well, I don't
know about the Mentec ones).

      Noel
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