Path: utzoo!utgpu!attcan!uunet!peregrine!elroy!gryphon!cadovax!mitchell
From: mitchell@cadovax.UUCP (Mitchell Lerner)
Newsgroups: comp.sys.next
Subject: Re: NeXT Memory - No Error Checking or Parity !
Keywords: Memory,errors,parity
Message-ID: <2302@cadovax.UUCP>
Date: 2 Nov 88 19:17:56 GMT
References: <549@gt-eedsp.UUCP>
Reply-To: mitchell@cadovax.UUCP (Mitchell Lerner)
Organization: Contel Business Systems, Torrance, CA
Lines: 38

In article <549@gt-eedsp.UUCP> jensen@gt-eedsp.UUCP (P. Allen Jensen) writes:
>Ok, Straight from a NeXT salesrep in response to the question:
>Q: Does the memory have a parity check bit ?
>A: "No"
>
>The reason was that "memory is reliable enough that the added cost
>was not justified."  If you have ever worked on some older equipment
>without parity, your opinion may differ.  Could an expert on RAM
>chips respond ?   Is memory really "reliable enough" ?

Well, where I work, we used to make machines that had parity checking
and then we made machines that didn't and now we make them that do again.

When I asked about this, I remember the answers that I got were something 
like this:

Older memories would/could fail one cell at a time and in this case it is
crucial to have parity checking logic in the hardware.  So this is why
we had parity checking in our older machines.

RAMs don't fail one cell at a time.  If a failure occurs in a RAM, the
entire bank will fail and other hardware detects that, and so, to have parity 
checking in a RAM type machine is a waist of time, money and space.
The customers though, don't know that parity is antiquated with newer
memories but they still ask for it.  And this is why we put it in our
newest machines; not because it could do anything useful, but as
a checklist item.  I belive that this is why IBM put parity in their
PCs.  And since IBM put it in their PCs, everybody thinks that it is
necessary for all machines.  In their PC, it certainly doesn't do anything!

This is what I heard, not necessarily is it what was said.  I may
be wrong.  And, it is certainly not a technical statement of Contel 
Business Systems.
-- 
Mitchell Lerner -- UUCP:  {ucbvax, decvax}!trwrb!cadovax!mitchell
	Don't speak to him of your heartache, for he is speaking.
	He feels the touch of an ants foot.  If a stone moves under the 
	water he knows it.