Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!lll-winken!lll-tis!ames!pacbell!belltec!jim
From: jim@belltec.UUCP (Mr. Jim's Own Logon)
Newsgroups: comp.sys.next
Subject: Re: NeXT Memory - No Error Checking or Parity !
Summary: RAM expert replies...
Message-ID: <296@belltec.UUCP>
Date: 31 Oct 88 15:56:10 GMT
Article-I.D.: belltec.296
References: <549@gt-eedsp.UUCP> <1988Oct28.210152.29417@utzoo.uucp>
Organization: Bell Technologies, Fremont, CA
Lines: 42

In article <1988Oct28.210152.29417@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes:
> In article <549@gt-eedsp.UUCP> jensen@gt-eedsp.UUCP (P. Allen Jensen) writes:
> >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" ?
> 
> I'm not really an expert on RAM chips, but I do know that the reliability
> of modern RAMs is *spectacularly* better than the ones that were routinely
> in use 5-10 years ago.

   According to the last court case I was a witness at, I'm an expert in 
memory system design. Credentials upon request. 

   While it is true that the reliability of RAMs being corrupted from 
spurious alpha partical hits has greatly increased this has actually left 
them more susceptable to other failures (which were more prevelant anyway).
The size of the memory cell, and the rate of leakage were what made earlier 
RAMs easy to have bit errors due to random alpha particals. The newer (larger)
RAMs have smaller cells and less leakage, making them more reliable.

   But, the main cause of memory corruption has always been noise. Electrical
noise from exrternal sources (generators, power surges, etc.), and from internal
sources (other chips, peripherals, power supply). The less the memory cell 
charge, the more susceptable to noise. 

   It is also very true that some vendors products are much more resilient to
signal noise than others (no, I won't name names). In this era of RAM shortage
you can bet that a company will be scatter buying their RAM to get as much
as possible and as cheaply as possible. It follows then that some of the
NExT machines will be better than others, some will never fail, some will fall
out in burn-in, and those in the middle....

   What should they have done? Make it a build option. If you want the extra
safety, you shell out the extra bucks. If you like going to Las Vegas, playing
the lottery, and Russian Roulette, you can have the base unit.


						-Jim Wall
						Bell Technologies, Inc.

The above opions are mine. However in this case, the company would probably
go along with them.