Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!cmcl2!rutgers!umd5!uvaarpa!virginia!kesmai!dca
From: dca@kesmai.COM (David C. Albrecht)
Newsgroups: comp.sys.amiga
Subject: Re: Argument for Virtual Memory
Message-ID: <146@kesmai.COM>
Date: Tue, 17-Nov-87 14:51:59 EST
Article-I.D.: kesmai.146
Posted: Tue Nov 17 14:51:59 1987
Date-Received: Sat, 21-Nov-87 00:45:51 EST
References: <2785@megaron.arizona.edu> <112@citcom.UUCP>
Organization: Kesmai Corporation, Charlottesville, VA
Lines: 47

Why are we hashing out the virtual memory bit again?
> What you have is a system that depends on the *user* to
> decide what permanent objects should be cached in fast memory and what
> should not, moment to moment.  This sucks.  The computer should
> automatically perform this function.  I. e., minimal virtual memory.
Me?  I spend the $30 to buy FACC which performs caching of frequently used
disk blocks.  It isn't equivalent to paging of memory but it achieves most
of what I need it for.  Most things come off a hard disk fast enough that I
wouldn't want to cache them in RAM:.  ANY resource allocater will throw out
something you haven't used in a while even if you don't want it to.  A
guaranteed way to lock items in memory ala. a RAM: disk is a plus even in
virtual memory systems.
> 
> lot's more stuff about some bizarro application which the author feels
> wouldn't be supported well without virtual memory.
>
Who cares?  I certainly don't.  It is true that virtual memory systems
make it possible to more efficiently use memory.  It is difficult to
have them do so without a memory speed access penalty (not to say that
it can't be done).  Virtual memory can make accessing of memory a much
more time erratic phenomenon.  It is a REQUIREMENT for virtual memory systems
to have a hard disk, paging memory to floppies is preposterous and there are
a hell of a lot of Amigas out there without a hard disk.  In any case with a
large enough memory space, virtual memory isn't really necessary.  My Amiga
has 2.5 meg which is enough memory for me to do virtually everything
I want (I dare say the same is true for 98% of the rest of the people
that use the machine).

You can certainly achieve the task you so ardently desire with existing
compilers 'safely', efficiently might be another matter.  You could write
a TSR style object manager just like which you would communicate
with through a message port to get pointers to
objects.  It would handle swapping in/out of objects etc.  You could 'lock'
the object as you make your reference then 'unlock' it.  It would probably
be slow as hell, but it would work.

I don't really miss not having virtual memory.  I do miss not having
interprocess protection.  Certainly, you can come up with applications for
which having virtual memory is a plus.  You can also come up with reasons
why being guaranteed that every page is in memory and immediately available
is a plus.  For the Amiga virtual memory wouldn't be a great idea.  On
any machine guaranteed to come with a hard disk, however, in my opinion
virtual memory is always a win just because it will let you more efficiently
use the memory you have.  With enough memory, however, it becomes a moot
point because you don't need to use it efficiently.

David Albrecht