And ...

I should mention that the origin of the bytecode interpreters was the
hardware of the Burroughs B5000, first described in print in 1961.  I used
this as a model for the Flex machine in the late sixties, including the
idea of overlapping contexts (it's a direct consequence of one way to have
the compiler map the stack). The B5000 also had HW flag bits to distinguish
its typed pointers from data, the ability to call procedures on the left
side of an assignment statement (so many kinds of data could be simulated),
automatic HW process switching, addressless bytecodes, segmented swappable
memory structures, etc. It was designed by one of the great geniuses of our
field (and unfortunately not remembered today), Bob Barton.

Cheers,

Alan

--------

At 7:34 PM -0800 3/29/00, Dan Ingalls wrote:
>I wrote...
>>> I'm sure this is true.  Ian wrote a context cache for an earlier Squeak and
>>it sped th
>>> ings up by about 50% as I recall.  What we have now is nicely simple, and
>>we've been h
>>> olding off on any serious tweaks until we can play around with J3
>>> (How's it going, Ian?).  J3 does even better things with the stack, which
>>allows the b
>>> asic interpreter to remain simple, yet offers a true high speed solution as
>>well.
>
>Tim Rowledge <tim at sumeru.stanford.edu> replied...
>>It's a relatively standard trick, with the first description that I know of
>>being the Deutsch/Schiffman 'Efficient Implementation of the Smalltalk-80
>>System' paper in 84 POPL proceedings.
>
>If we are talking about putting contexts in the hardware stack, I did this
>half a decade earlier.  Smalltalk-78 ran on a 4MHz 8086(*).  The VM was 6K
>of code.  And it put its contexts right in the hardware stack.  I also
>used the trick of overlapping adjacent contexts so there was no need to
>transfer arguments (Ian and I have been discussing doing this for Squeak
>-- it requires pushing the receiver last instead of first).
>
>You can read this and other tales of early Smalltalk VMs in my chapter of
>the "Green" book edited by Glenn Krasner.
>
>	- Dan