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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.arch
Subject: Re: PDP-8
Message-ID: <6514@utzoo.UUCP>
Date: Fri, 14-Mar-86 16:50:22 EST
Article-I.D.: utzoo.6514
Posted: Fri Mar 14 16:50:22 1986
Date-Received: Fri, 14-Mar-86 16:50:22 EST
References: <187@anwar.UUCP> <1441@gitpyr.UUCP> <890@umn-cs.UUCP>
Organization: U of Toronto Zoology
Lines: 24

>  	The PDP8  has an interesting peripheral : a 'parallel'
> processor - the FPP12 floating point processor with its own instruction
> set, program counter and accumulator...
> ... A nice system for doing real time I/O (via the CPU) and
> number crunching (FPP)...

It was more than that, in fact.  The FPP was a much better processor than
the PDP8!  It had index registers.  It had uniform 15-bit memory addresses
rather than 3+12 bits.  It could do integer arithmetic as well as floating-
point, and as I recall could do 24-bit integers.  (If you think 32 is an
improvement over 16, try 24 versus 12!)	 The one thing it couldn't do was
I/O; for pretty nearly everything else, it was *better* than its host!
In fact, the very late PDP8s acknowledged this by having an instruction
that would stop the PDP8 itself until an interrupt occurred, so that the
FPP could use the full memory bandwidth.

> (If only 32k memory was enough!)

16K was a lot of memory on a PDP8...  Our lab had to fight tooth and nail
to get 16K accepted as our official configuration, so that the software
could rely on it.  Before that, we routinely worked with 8K.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry