From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: f849b,b8d52151b7b306d2
X-Google-Attributes: gidf849b,public
X-Google-Thread: 103376,a00006d3c4735d70
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-12-28 15:03:31 PST
Message-ID: <3fef6140_2@mk-nntp-1.news.uk.worldonline.com>
From: Ian Bell <ian@ruffrecordsDOTworldonline.co.uk>
Subject: Re: Certified C compilers for safety-critical embedded systems
Newsgroups: comp.arch.embedded,comp.lang.ada
Followup-To: comp.arch.embedded
Date: Sun, 28 Dec 2003 23:06:21 +0000
References: <3fe00b82.90228601@News.CIS.DFN.DE> <3FE026A8.3CD6A3A@yahoo.com>
 <$km9afA3DB7$EAYO@phaedsys.demon.co.uk>
 <bcEFNEK9esyI@eisner.encompasserve.org>
 <p$OIcVFWHL7$EA6t@phaedsys.demon.co.uk>
 <wccekur4151.fsf@shell01.TheWorld.com>
 <Xns945DE49836882jimmaureenrogers@204.127.36.1>
 <yA9Hb.488862$275.1387889@attbi_s53>
 <Xns945E85FD3E1Bjimmaureenrogers@204.127.36.1> <3FEDDD73.C0CFAE19@yahoo.com>
Organization: REMAP
User-Agent: KNode/0.7.2
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7Bit
NNTP-Posting-Host: dial-62-64-200-181.access.uk.tiscali.com
X-Trace: 28 Dec 2003 23:03:29 GMT, dial-62-64-200-181.access.uk.tiscali.com
Path: 
 archiver1.google.com!news2.google.com!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!kibo.news.demon.net!demon!mk-nntp-1.news.uk.worldonline.com!dial-62-64-200-181.access.uk.tiscali.com
Xref: archiver1.google.com comp.arch.embedded:6243 comp.lang.ada:3903
Date: 2003-12-28T23:06:21+00:00
List-Id: <comp.lang.ada>

CBFalconer wrote:

> James Rogers wrote:
>> 
> ... snip ...
>> 
>> When reliability engineers encounter a system relying upon human
>> actions the commonly accepted error rate, assuming properly trained
>> humans, is 1 in 1000. Such an error rate is unacceptably low for
>> most safety critical systems. An error rate of 1 in 1000 is a
>> reliability rate of 0.999. Safety critical systems commonly
>> require reliability rates on the order of 0.999999. This is
>> three orders of magnitude higher than can be achieved through
>> reliance on human correctness.
> 
> And even then, 1000 such 6 nines reliable systems together can be
> expected to have a combined reliability of 0.999.  Now consider
> the count of individual transistors in a moderately complex
> processor.
> 
> There are two basic methods of improving the end product
> reliability:  Improve the component reliability, and reduce the
> number of components.  This argues heavily against using a Pentium
> when a PIC will do.
> 

Interesting argument but a potentialy flawed example.  First one pentium and
one pic are each one component so no reduction in components. More
importantly, though a Pentium may have more transistors in it than a PIC
and hence might be seen as more complex, it is not necessarily less
reliable.  Indeed given the relatives quantities manufactured the pentium
might well be much more reliable than the PIC.

Ian