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Path: utzoo!utcsstat!geoff
From: geoff@utcsstat.UUCP (Geoff Collyer)
Newsgroups: net.news,net.news.group
Subject: portability and re-writes
Message-ID: <1953@utcsstat.UUCP>
Date: Mon, 4-Jun-84 05:33:38 EDT
Article-I.D.: utcsstat.1953
Posted: Mon Jun  4 05:33:38 1984
Date-Received: Mon, 4-Jun-84 05:45:22 EDT
References: <210@homxa.UUCP> <1941@utcsstat.UUCP> <221@homxa.UUCP> <676@ru-cs44.UUCP>
Organization: U. of Toronto, Canada
Lines: 95

I'm going to comment further on Dave Anderson's remarks.

I said

	The attitude that "Gee my VAX has a 6 megabyte data space, so
	no one needs to ever think about memory constraints" is
	widespread and dangerous.

Dave said

	Very true. But it is the progressive view, and I'd rather push
	the limits than be forced to hang back.

Don't confuse ``popular'' with ``progressive''.  If the progressive
view is dangerous (ruinous, not risky) then I'll be regressive,
thanks.

I said

	It is possible to fill even a 6 megabyte data space. The
	advantage of facing memory constraints squarely is that your
	programs have a good chance of running on even quite small
	machines. Portable programs can not assume a 6 megabyte data
	space.

Dave said

	Why not? Paging allows an address space as big as the moon. If
	you worrying about the physical length of an address, well, I
	grieve for you. That's why we got rid of our PDPs.

Wrong (unless ``the moon'' is pretty tiny).  Paging allows a finite and
sometimes surprisingly small address space.  I believe that in 4.1BSD
and 4.2BSD as delivered that limit is 6Mb of data.  I can't speak for
Uglix (system n).  No matter what that limit is on your machine, failing to
design programs to deal with limited memory is often due to sheer
laziness and is often the mark of an amateur programmer.  (I realise
that this is not always the case.)

Portable programs must attempt to run on machines with small memories
since by definition if a program doesn't run on small machines it is
significantly less portable than those programs that do run.

I said

	B news is not wonderfully portable ... some will say that if
	expanding news limits breaks PDP-11s ... it's further
	justification for getting a machine with a bigger virtual
	address space. There certainly are legitimate needs for bigger
	virtual address spaces and people hereabouts are looking at
	machines with same, but in the case of news, I think the
	problem is poor design. News needs a re-write.

Dave said

	Yeah, news is due for a re-write. Version 3.0 should include
	screen control, user supergrouping, special bulletin boards,
	etc.  We'll see 2.11 first. But as far as I know, nobody's out
	there writing it. The design of 2.10 is not poor - it is a
	product of software evolution.  But the real question of
	virtual addressing will bite you in the end.  Sure, you can
	still do alot without it. But the limitations are too great.
	Why isn't there anyone using PDP-8's to read news? or 8080's? I
	think that you ought to at least upgrade to a 32 bit machine.
	At least while you can still unload your PDP's; Soon nobody may
	want them.

Don't assume you'll see 2.11 news *ever*.  I'm going to come out of the
closet and admit that I am one of the two people who volunteered to
maintain readnews.  We have the choice of cramming an elephantine
2.10.1+some readnews into PDP-11s or throwing it out and doing it
properly;  I hope to throw it out.

Damn, man, have you ever *looked* at the 2.10 sources? I keep a special
pair of welder's goggles for looking at the sources.  2.10 is not a
product of evolution: it's an ugly hack, hacked and rehacked until it
can't be hacked no more.

I have just written rudimentary inews and readnews in the shell, and
each is 38 lines long.  So the limitations of memory are *not* too
great for a news system.  The shell programs are slow and don't do all
the things their B news counterparts do, yet, but they demonstrate that
address space limits need not be a serious problem for the news
programs.  This whole discussion about address space size is a bit of a
red herring.

I'll always want my PDP-11; it's the only UNIX machine I administer
that runs v7.

Dave said

	How long till we all need 64 bit addressing?

If we start *needing* 64 bit addressing for a measly news system, then
computing is doomed.