Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!sdd.hp.com!elroy.jpl.nasa.gov!decwrl!public!valentin
From: valentin@public.BTR.COM (Valentin Pepelea)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Virtual Memory Program?
Message-ID: <1986@public.BTR.COM>
Date: 2 Mar 91 08:27:16 GMT
References: <1991Feb14.193510.13772@bradley.bradley.edu> <%1+-SC%@irie.ais.org> <1991Feb20.175103.24611@jato.jpl.nasa.gov>
Organization: BTR Communications, Mtn. View, CA
Lines: 25

In article <1991Feb20.175103.24611@jato.jpl.nasa.gov>
jdickson@jato.Jpl.Nasa.Gov (Jeff Dickson) writes:
>
>	To support a virtual memory application (more like a virtual disk),
>is it safe to assume that the application will only use AmigaDOS to access
>the file's contents? Without an MMU I don't see any other way. Comments?

You are indeed right. The problem with accessing a disk directly through
its device driver is that the device driver does not know when it is not
allowed to DMA into a portion of memory. As for the AmigaDOS filing system,
the MASK value in a mount list identified the region of memory into which
DMAing is allowed. So files may be loaded into virtual memory only through
the filing system.

Obviously, DMAing into virtual memory is not possible without the full
support and knowledge of the operating system. But then, I don't know
of any operating system offering the possibility of DMAing into virtual
memory. No wonder considering the futility of such an exercise.

Valentin
-- 
"An operating system without virtual memory      Name:      Valentin Pepelea
 is an operating system without virtue."         Phone:     (408) 985-1700
                                                 Usenet:    mips!btr!valentin
                     - Ancient Inca Proverb      Internet:  valentin@btr.com