From: martin@DMI.USherb.CA (Jean-francois Martin)
Newsgroups: comp.sys.mac.misc
Subject: STOP: THE MAC COST TOO MUSH
Date: 30 Aug 92 14:37:56 GMT
Article-I.D.: DMI.Btswn9.MGo
Reply-To: martin@DMI.USherb.CA
Organization: Universite de Sherbrooke -- Dept. De Mathematiques et D'Informatique

In article 715040512@husc10, ajross@husc10.harvard.edu (Andrew Ross) writes:

>     THE PC IS NOT LIMITED TO 640K.
>
>This is a .DOS. limitation.  It stems from the fact that the original 8086
>processor had only 20 address lines and thus could address only 1MB of
>real memory.  This processor used a segmented address mode where a
>complete address was specified by two bytes:  one being the address within
>the segment and the other being the "segment offset", or number of 4k
>blocks into the memory the segment started.  Each segment was therefore
>64k long, the idea being that a program would reside in only one segment
>or so, thus an address reference would usually require only one byte. 
>When IBM picked the 8088 (the 8-bit memory bus version of the 8086) for
>its PC, 1MB was seen as a ridiculously large amount of memory for a
>microcomputer.  Thus when DOS was written, it reserved the top 384k for
>things like video memory and the like ("640k should be enough for anybody."
>--Bill Gates. ;)  When intel designed the 80286, they included the same
>segmented design for backwards compatibility; they also added a "protected
>mode" to the processor in which it could address the full 16MB provided by
>its 24 address bits.  The next generation 80386 (and the i486, which uses
>the same memory scheme) had 32 bit addressing and could access 4GB of real
>memory.  OS/2 and all PC unixes use the 386's protected mode exclusively
>and therefore have access to ALL THE MEMORY THE PROCESSOR CAN HANDLE
>(though there is a problem for some machines at 16MB, read on).  Windows
>uses this mode for most of its native operations, but since it has been
>launched from DOS, and has to multitask DOS programs, still relies on the
>segmented model to some extent.
>
>Most machines with the AT (Industry Standard Architecture - ISA) type of
>expansion bus, however, run into another type of barrier at 16MB.  This
>expansion bus, being designed for the 286, has only 24 address lines. 
>This means that anything attached to it (hard drive, floppies, video,
>pretty much everything) can only read and write into the lowest 16MB of
>memory.  OS/2 deals with this by calling anything above 16MB on these
>machines a kind of "Virtual Memory" which it uses as swap space in the
>same way that disk-based VM is used.  Micro Channel machines (PS/2's) and
>Extended ISA (EISA) based machines do not have this limitation. 
>
>Some quick definitions for Mr. Wright:
>
>Extended Memory - This is the term used for all the memory above the first
>                  1MB in a DOS (not OS/2 or Unix) machine.  It is not a
>                  hack or a fix, just a term.
>
>Expanded Memory - This is a hack.  In old DOS machines, extra memory was
>                  often used by swapping chunks in and out of blocks in
>                  the high memory.
>
>High Memory - The space between 640k and 1MB.  DOS can use it, but not for
>              standard programs.
>
>OS/2 2.0 - Fantastic operating system you obviously haven't used which
>           makes all the above definitions irrelevant.
>
>>>You Should check out the PC world, much has and is happening (the
>>>great thing about competition).
>
>>Look, kid, I've already stated this several times, but 
>>since you obviously have trouble reading, I'll state it
>>again, in capital letters just for you: I AM TYPING THIS
>>ON A PC.  I USE A PC EIGHT HOURS A DAY -- MORE THAN I USE
>>THE MAC.  I don't need to "check out the PC world," I am
>>already more familiar with it than I really care to be,
>>probably more familiar with it than most people here, and
>>obviously a hell of a lot more familar than you.   
>
>Most office assistants and students use PC's that much.  This does not
>make them experts.  Using a machine for what it is intended to do teaches
>you nothing about its internals.  This is equally if not more true on the
>Mac.  Please back up you attacks with evidence.
>
>I have to get one flame in here:
>
>IMHO, someone who suports his office's decision to pay $7000 for a
>386-20 and $600 for a Video Accelerator and thinks all PC's are limited to
>640k doesn't know sh*t about PC's.  Please grow up.
>
>Andy Ross
>ajross@husc.harvard.edu
>                                               that's right, no .sig
>
>

At least an good article on the PC. Not a flame that we get used to see on
this newsgroup. For the others, stop bashing everybody else who don't
use the same computer as you do. PLEASE, STOP THE THREAD: THE MAC COST TOO MUCH.


---
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= Jean-Francois Martin                                     martin@dmi.usherb.ca=
= Graduate student of Universite de Sherbrooke (je parle francais)             =
= "In complete darkness we are all the same" Janet Jackson                     =
================================================================================
Newsgroups: comp.sys.mac.misc