Xref: utzoo comp.sys.ibm.pc:28076 comp.sys.amiga:32925
Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!mcnc!rti!bcw
From: bcw@rti.UUCP (Bruce Wright)
Newsgroups: comp.sys.ibm.pc,comp.sys.amiga
Subject: Re: OS/2 vs AmigaDOS
Summary: OS/2 vs other operating systems
Message-ID: <2921@rti.UUCP>
Date: 29 Apr 89 03:29:06 GMT
References: <2134@iitmax.IIT.EDU>
Organization: Research Triangle Institute, RTP, NC
Lines: 57

In article <2134@iitmax.IIT.EDU>, ed@iitmax.IIT.EDU (Ed Federmeyer) writes:
> 
> I don't really have much of an opportunity to use OS/2 or AmigaDOS, but I
> couldn't help but wonder how different the two opperating systems are?
>  
> I don't understand why OS/2 uses 3 Mb of RAM (I think I read that somewhere) to be usefull, while with AmigaDOS you only need 256 Kb.  What does OS/2 give
> you that AmigaDOS doesn't?  After all, they both multitask, have graphics
> based interfaces, etc...  Is it maybe because the 68000 assembly language
> is more compact than 80286 or 80386?

It really isn't any mystery why OS/2 is so enormous.  Oversimplifying
outrageously, the reasons are:

    o	The segmented 80*86 chip architecture

    o	The O/S designers at Microsoft.

The problem with the 80286 chip in particular is that because it is 
a segmented architecture, and because paging is difficult to impossible,
it turns out that it is inconvenient to deal with memory except in rather
large chunks.  This means that when a segment is required, the entire
segment must be loaded;  if you have a LOT of memory this may not be
very bad, but it IS very memory intensive.  The 68000 does not have
this architectural problem (nor does the 80386 running in native mode,
but even allowing for that the 80386 even in native mode looks ugly
beside the more modern 68k chips).

The problem with the O/S designers at Microsoft is that they had a
tendency to require that everything be preallocated - there is rather
little use of things like a "pool" or "free memory" area compared to
many other operating systems (it does exist, it just isn't used to the
extent that it is in many systems).  Part of this may be a desire to
ensure that you don't run out (the effects of this can be mysterious
even to experienced users - imagine the consternation of a secretary
when the PC runs out of something as esoteric as "pool space").

If you don't require the DOS compatibility box the size of the machine
required to run OS/2 goes down quite a bit - that little convenience
costs you quite a bit of *PERMANENTLY ALLOCATED* memory.  Unfortunately
because of the existence of abominations like Sidekick and other hostile
DOS applications, there is not much that Microsoft can do about that.

Unfortunately all these things work together and enhance each other's
bad points to create an operating system which uses much more memory
than one would normally think would be necessary.

By the way, I am in NO WAY surprised at the amount of memory required
to run OS/2 EFFICIENTLY - many multasking operating systems with window
environments and complex software ARE able to use a LOT of memory (just
look at VMS ...) but most of them don't degrade as DRASTICALLY as OS/2
does when there isn't 4MB of memory available.  I AM surprised at how
BADLY and QUICKLY it degrades as it runs out (usually it's more of a
slow degradation rather than a brick wall).

Anyway, I've probably annoyed enough people this evening.

						Bruce C. Wright