Path: utzoo!attcan!uunet!samsung!usc!apple!vsi1!zorch!xanthian
From: xanthian@zorch.SF-Bay.ORG (Kent Paul Dolan)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Parity Checking / ECC RAM on the A3000
Summary: probably a good idea
Keywords: parity error detection and correction, marketability
Message-ID: <1990May27.101258.24470@zorch.SF-Bay.ORG>
Date: 27 May 90 10:12:58 GMT
References: <756@bilver.UUCP>
Organization: SF Bay Public-Access Unix
Lines: 40

In article <756@bilver.UUCP> alex@bilver.UUCP (Alex Matulich) writes:
>
>However, the fast RAM chips are replaceable by the 4 meg variety.  You can
>stick 16 of them in the A3000.  That's a potential for 16 parity errors
>per day!
>
>I think I would worry about that.  I wouldn't want a scientific experiment
>or financial program go off using erroneous data without knowing it.
>Three extra parity bits per byte would allow detection of up to 2 bits and
>correction of one (per byte).  This is very complicated to design, however.
>Single-bit parity error detection (like one has on IBM compatibles) is
>relatively easy.

Computer folk wisdom has it (actually, I had this from someone at the NCAR
site where the beast was then installed) that Seymore Cray built Cray 1
number 1 without parity checking.  The error rate in that much memory was
insufferable, so the machine became a sort of demo machine; when you ordered
a Cray 1, you first got serial number 1 installed, on which you could build
and test your code in a lossy environment, until a machine with parity could
be built for you and swapped for the useless toy first delivered.

The Amiga 3000 is capable of holding (at least supporting) much more memory
than a Cray 1, and the size of gates in modern memory is much smaller and
thus they are more susceptable to alpha radiation induced parity errors than
were the gates of the Cray memory.

To take an Amiga seriously as a commercial machine in the "workstation,
large memory" market, I'd guess error correcting code will turn out to be
vital.  It would be a shame to have a big production run of the hardware
installed and on the street, only to have parity problems give the machine
a reputation as an unreliable machine, to be avoided in droves.  Better if
the problem is solved before the reputation is besmirched.

But then, what do I know after 29 years in the field about what people who
buy the machines look for in a large processor?  My computer purchases were
limited to a couple of million bucks worth, down in the noise level in the
marketplace.  ;-)

Kent, the man from xanth, now zooming to the net from Zorch.
(xanthian@zorch.sf-bay.org)