Re: how can a bit be off in memory?

ray wrote:
On Fri, 29 Jun 2007 23:58:48 +0200, Charles T. Smith wrote:

Vim started crashing on me, particularly when I tried to open new lines. I finally checked it out with rpm and a newly downloaded copy of vim's
rpm and discovered that exactly one byte, deep into vim, was wrong.

I rebooted my machine (which has been super-solid for years) - and the
difference was gone.

So, what are the opinions - did I run into a hardware glich, or was
there a freaky issue with memory mapping?

I think I'd run 'badblocks' on the disk.

Oh..I had this years ago - and repeatably too..on a machine with some third party hardware in it.

Two bytes were FF on a file loaded from the floppy disk.

It turned out to be a timing issue: At a given point the DMA was doing its stuff, and the IO address momentarily passed that assigned to the 3rd party card, which was slow on decoding it, that it thought it was still there when the IO line went up..and so the card grabbed the bus and plonked an 'all ones' 16 bit on the thing..

My guess is yo have some marginal hardware in the system, and maybe the weather was warm, and the transfer from disk just happened to be in an area of memory that excited the bad hardware..

In other words a confluence of events conspired..

Never believe that computers are 100% reliable,. A friend spent some time years ago developing hardware: they ran into an interrupt timing issue. Every 4-5 hours the machine would crash when a timer interrupt interrupted a particular piece of code. For reasons deep and complex, they couldn't turn interrupts off, but the managed to re-code the bit of code so the offending part was very small, and they calculated the crash would occur only once in every 5 years or so.

They left it that way, knowing that occasionally a user would scratch his head, reboot, and shrug his shoulders 'I wonder what THAT was?' :-)
:-)

ONE bad byte is indicative of an 8 bit peripheral misbehaving. Its NOT indicative of a memory or disk error...those happen at the bit level and generally result in an error being flagged.

The odd thing is that your on-disk copy got corrupted..or was it? Or was it the LOADED copy that was corrupted?
.

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