Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!ubc-cs!alberta!calgary!xenlink!blender!bruce
From: bruce@blender.UUCP (Bruce Thompson)
Newsgroups: comp.arch
Subject: Re: SCSI on steroids, mainframes move over
Message-ID: <90@blender.UUCP>
Date: 2 Sep 89 03:56:11 GMT
References: <5932@pt.cs.cmu.edu> <3238@scolex.sco.COM> <26970@amdcad.AMD.COM> <452@ctycal.UUCP>
Organization: Some apartment in downtown Calgary
Lines: 31
Summary: Quicky reference regarding file/segment mapping

Just a quick (I hope :->) note about file mapping.

Apollo workstations provide a technique called Mapped-Segments which allow
a process to link a file into it's virtual addressing space thus reducing
I/O times to paging times. The interesting thing is that the documentation
for the `Open System Toolkit', mentions that the `uasc' file manager uses
mapped segments to implement unstructured ascii files (like regular UNIX
files).

Some quick background: The Apollo file system is object-oriented. Each
file-system entry has a type, like `uasc'. Each type has a manager which
is a set of functions which know how to manipulate objects of that type.
When a file is opened, the appropriate type manager is called to perform
the operations on the file. You can write managers which call other
managers, so if you were to create a `structured ascii' file type you
could use the `uasc' manager to handle operations which you do not want to
directly deal with.

An interesting side note, mapped segments can (and are) be used to
implement shared memory between processes.

------------------------------------------------------------------------
Bruce Thompson
CAE Engineer, NovAtel Communications Ltd.
1020 64 Ave, N.E., Calgary, Alberta, CANADA

Disclaimer: I do not represent in any way the views/policies of my
employer, and often not even my own.

"Never underestimate the power of human stupidity"
	- Lazarus Long