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Re: is it sensible to think of an extended address Lisp for the DEC-20?

I agree entirely with Tom's remarks about the worth of an extended
Lisp for the -20.  Most sites are facing a 5-year wait before personal
machines will be powerful enough and cheap enough to even consider
giving one to each senior research type; and, most of us can't afford
to leave behind all the -20 software and jump on the VAX bandwagon as
long as there are -20's in our stables.  The 2080 will make the
economics of using larger-scale machines even more attractive, at
least for 3-4 more years (in case people haven't heard much about the
2080, it's a machine 3-5x the speed of a 2060 for a little less cost,
with high internal redundancy for reliability (the first field test
CPU will probably show up at MIT in 9-11 months, though it won't reach
the marketplace for another 1.5 years); it will also have an Ethernet
interface as a standard part of the front-end, with a Xerox 5700 (or
something similar) as a page printer option).

However, Guy is entirely right about the horrific kludginess of the
-20's extended addressing scheme.  It's only practical to consider
using it in something like the NIL project, which is based on a
machine-language kernel of modifiable size and which can afford to
suffer the slings of outrageous address structures.  It's probably
useless to toy with the idea of modifying systems such as MacLISP and
Interlisp, which are rife with assumptions about cons cell structure.

(BTW, what ever happened to BBN's proposal to microcode the Prime 750
to run Interlisp, just out of curiousity?)