short answer to technical question?

Crisler, Jon JCrisler at corvis.com
Wed Nov 16 21:40:53 UTC 2005


Older IBM AS/400's used 128 bit addresses since 1988, and this was true
from ver 1 of OS/400 until past ver 3 of OS/400.  I think this allowed
the concept of single-level storage, where all disk was addressable the
same as memory.  The initial CPU was a true 48 bit machine IIRC, and
went to 64 bit when the Power PC first came out in that flavor.

-----Original Message-----
From: fedora-list-bounces at redhat.com
[mailto:fedora-list-bounces at redhat.com] On Behalf Of Nix, Robert P.
Sent: Wednesday, November 16, 2005 3:26 PM
To: 'For users of Fedora Core releases'
Subject: RE: short answer to technical question?

Actually, in this case 32 bit and 64 bit refer not to the natural word
size, but to the address size. i.e. a 32 bit machine uses a 32 bit
address for memory, and cannot address as much memory as a 64 bit
machine, using 64 bit addresses, can.

In the case of the IBM mainframe computers, the natural word used to be
32 bits, but they were 31 bit machines, as the top bit of the word was
reserved for something other than an address bit. The new mainframes are
64 bit machines, using all 64 bits of an address to address memory.
They're still 32 bit words though; they just happen now to use two of
them for an address. 

(Actually, the smallest thing the mainframe would deal with for a long
time (early 1980's forward) has been 64 bits, or a double-word. The main
change has been the use of larger addresses.) 


-- 
Robert P. Nix		Mayo Foundation
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-----
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 in practice, theory and practice are different."

-----Original Message-----
From: fedora-list-bounces at redhat.com
[mailto:fedora-list-bounces at redhat.com] On Behalf Of Mike McCarty
Sent: Wednesday, November 16, 2005 12:21 PM
To: For users of Fedora Core releases
Subject: Re: short answer to technical question?

Gerhard Magnus wrote:
> Hello All,
> 
> 	I don't know if there's a short answer to this... but what do
"32 bit"
> and "64 bit" refer to and how can I tell which applies to my computer?
> 
> Jerry

Modern PC style computers all are binary. (Most calculators are
decimal.) The word "bit" is a contraction of "binary digit".
All computers have a natural word size, measured in digits.
This is the size of word which the computer can use without
special software. If the natural size of a computer word is
8 bits, then it is called an 8 bit computer. Examples are the
8080, Z80, 68HC11, and so on. Computers whose natural word
size is 16 bits are the 8086, Z8000, 68000, etc. The 80386
and later 80x86 machines up through the Pentium class machines
were all 32 bit machines. Now, some machines have a natural
word size of 64 bits.

The only way to tell is to know what the processor chip is.

Mike
-- 
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I can explain it for you, but I can't understand it for you.
I speak only for myself, and I am unanimous in that!

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