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Error Correction (WAS: Utility to test IDE cable connections?)
David R wrote:
.... snip ... The "duff" cable worked. But it was giving errors. XP seemed to detect them but they did not seem to be critical in the sense of preventing data being stored. However if I could not sense the cable was "duff" and the errors were indeed critical then I would be in trouble. This is what I want to avoid. Normally the HD system stores and recovers data using various error detecting protocols, and will do a retry if the action fails. This doesn't generally cover the transmission over those cables, however, but any faults there should be fairly gross and are not likely to go undetected. However, the memory in your system, if not protected with ECC, is another matter. There an error will be totally ignored. Here is something I wrote about two years ago: A Tale of Two Machines - by Charles Falconer :-) or What the Dickens ============================================ Your system is updating or moving a file. This may be the operation of a database application, disk defragmentation, the opsystem updating the last accessed date, or almost anything. At some point in the operation the data is residing in memory. Here comes a cosmic ray which trashes some bit. The result is written out to storage as a valid value. Nothing special happens. One week, month, year later you access that data, or use the executable file that was fouled, and possibly something obvious happens. Or not, it may just result in trashing some further dependant data, and the obvious fault gets postponed further. In the interim you have dutifully made backups. By now the backups you made before that cosmic ray happened are long gone, overwritten, and probably pretty useless even if you still have them, because most of the data on them is obsolete. So you restore everything, including that fouled file or files. Maybe the fault shows up again, and you start swearing at the hardware, software, wife, dog, whatever. Maybe it waits around for another period before showing up. But it is lurking there, waiting to bite at the worst possible time (Murphy ensures this). Still no sign of hardware troubles. The memory checks out perfectly (unless you get a suitable cosmic ray during the check). Backups still do no good. Neither does cursing. How many days or weeks have you now lost? Your customer has long gone elsewhere. How many irate calls to some ignoramus on some help desk have you placed, and at what cost? You may well resolve it by a full reinstall, but if the fault is in your own data that won't help either. If you go and buy a new machine and install those backed up faulty data files the error follows right along like a tame puppy dog. Or, another scenario, the dropped bit changes an accounting value. The resulting reports are off a few dollars (or more, ever hear of someone getting a pay check cut for an extra million?). Your customers curse you for flakey service, and go elsewhere. Maybe the IRS gets snitty about something that doesn't balance, and attaches your whole business. Murphy carries on. Here comes the second machine. Now consider the system with ECC memory installed, enabled, and functioning. It probably slowed down by some fraction of one percent. Did you notice? It probably cost you twenty to a hundred US dollars extra. Did you really notice? However, the ECC memory system noticed the cosmic ray effect, and corrected it immediately. You certainly didn't notice that. But neither did you notice all the other potential problems that could appear on the non-ECC machine. Of course you COULD get along without the ECC and be lucky. You COULD indulge in unsafe sex with some stranger and be lucky. You COULD ignore that red light and be lucky. At least the cause and effect are obvious in the red light case. My recommendation: ALWAYS insist on ECC memory. -- Chuck F ) ) Available for consulting/temporary embedded and systems. http://cbfalconer.home.att.net USE worldnet address! |
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