Newsgroups: comp.sys.mac.misc
Subject: Re: MACS COST TOO MUCH (NOT!)
From: ajross@husc10.harvard.edu (Andrew Ross)
Date: 28 Aug 92 22:21:52 GMT
 <ewright.714943016@convex.convex.com> <1992Aug28.063440.28863@CS.ORST.EDU> <ewright.715017293@convex.convex.com>

ewright@convex.com (Edward V. Wright) writes:

>In <1992Aug28.063440.28863@CS.ORST.EDU> pricec@prism.CS.ORST.EDU (price carl wayne) writes:

>>Strange, my PC has a memory limit of 4GB without any of the expanded et al.
>>BS.  

>You said it.  BS indeed.  The PC has a memory limit of 640 kilobytes.  
>Not megabytes, *kilobytes*.  Memory beyond that barrier cannot be
>addressed without resorting to tricks such as those used by Microsoft
>Windows.  Tricks that don't always work, which is why Ventura Publisher
>for Windows, for example, cannot multitask with any other Windows program
>no matter how much physical or virtual memory you have installed.  If you
>don't believe me, just call Ventura technical support and *ask*.

I'm sorry, but I'm losing my patience here.  This has been stated again
and again.  Let me say it explicitly:

     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