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From: reiter@pandora.UUCP
Newsgroups: comp.arch
Subject: Re: What should be in hardware but isn't (LISP hardware?)
Message-ID: <2913@husc6.UUCP>
Date: Wed, 30-Sep-87 18:27:26 EDT
Article-I.D.: husc6.2913
Posted: Wed Sep 30 18:27:26 1987
Date-Received: Sat, 3-Oct-87 01:31:58 EDT
References: <581@l.cc.purdue.edu> <28200048@ccvaxa> <2910@ames.arpa> <2917@ames.arpa>
Sender: news@husc6.UUCP
Reply-To: reiter@harvard.UUCP (Ehud Reiter)
Organization: /etc/organization
Lines: 35
Keywords: LISP and Prolog machines

In article <2917@ames.arpa> eugene@pioneer.UUCP (Eugene Miya N.) writes:
>It's pretty obvious to putting vector and floating point hardware
>in Silicon with products like the Weitek, but ...
>  what about putting CDR hardware into machines?
>The colleague pointed out that SUN is the only company doing well in
>this arena.  Agree or disagree?  Aren't Symbolics, TI, LMI doing okay?

The last I heard, the various LISP companies were in trouble because of
stagnating sales (i.e. sales are constant - they're not decreasing),
which could be as much due to market saturation as anything else.

Technically, CDR is just a pointer operation and is trivial to implement
on any machine.  The special hardware that LISP machines tend to have are:

   1) Tagged data.  The tags give data type.  A word in memory might, for
example, consist of 32 data bits and a 4 bit type field.  Note that in LISP,
variables are not typed, so the types of data elements in an operation may not
be known at compile time.

   2) Memory management.  Support for CONS and for garbage collection.

   3) Special caches, instruction sets, etc., which are geared towards LISP.

[This list is by no means exhaustive]

Whether LISP machines give any price/performance advantage over conventional
machines is unclear.  I once looked into this, and received highly
contradictory data.  In any case, since LISP tends to be a "research"
language (as opposed to a "production" language), most LISP people are
more interested in good software development environments than in hardware
speed.

					Ehud Reiter
					reiter@harvard	(ARPA,BITNET,UUCP)
					reiter@harvard.harvard.EDU  (new ARPA)