Subject: Re: Inquiring minds want to know.
To: None <>
From: Aaron J. Grier <>
List: port-alpha
Date: 05/21/2003 14:22:29
On Sat, May 17, 2003 at 11:15:08PM +1000, Collin Baillie wrote:
> I'm wondering if anyone out there can extoll the differences between
> the Alpha 64-bitness and the new Opterons.  I know the opteron is a
> glorified x86 box, but how does it stack up (theroetically) against
> the Alpha?

I'm curious about this, too.  I seem to recall that AMD used some of the
same bus interfacing that Alpha did.

> And while I (kind of) know the difference between Little Endian and
> big Endian, I've never really learned what the real difference is and
> it might be advantageous to have one or the other.. Is anyone
> interested in explaining this to me as well?

if you're on a little endian system, if you have the address of a
variable and want the lowest byte, you just do a byte read at that
address.  for a big endian system, you have to know a priori what the
size of the variable at the address is before you can get the lowest

let's write the 32-bit value 0xaabbccdd into memory location zero:

addy	BE	LE
00:	aa	dd
01:	bb	cc
02:	cc	bb
03:	dd	aa

if I want to read the lowest byte (dd) on a little endian system, I
always know it's at address zero, no matter if the variable happens to
be a 8, 16, 32, or 64 bits.  for a big endian system, the location of
that lowest byte changes depending on whether the variable is 8, 16, 32,
or 64 bits.

whether or not it's useful is debatable.  :)

  Aaron J. Grier | "Not your ordinary poofy goof." |
      "It's not fast, but why not?"  --  John Klos on VAX dnet client
  "because it needlessly contributes to global warming?"  --  Paul Vixie