Thursday, July 27, 2006

For the want of a screw I reached tipping point

I'll start with the happy ending.
My PC at home is working.

I'll continue with the apology.
It's Windows XP and not Ubuntu (but it does SUSE on occasion).

And this has nothing to do with Malcolm Gladwell.

Shortly before moving house I got a PC. A work colleague (I hate the term coworker) and hardcore gamer needed to sell his machine. Or rather his wife wouldn't let him have another PC. Me, I'm now on 4.

Any suggestions for the good use of old PCs?

Anyway, it took me almost a year to get around to using the PC.
I crashed after 10 minutes. Actually that's a bit general. Sometimes it lasted 30 minutes, sometimes 45 minutes.
I always got an "out of range" error message.

Having worked in tech support I know the most likely cause of the error.
The bloody thing had been moved an tossed about a little during the house move. Most likely there is a loose cable. (Do you expect a hardcore gamer to not play any less than 3 hours at a time? Me neither.)

So, naturally, it took me a few months to get the thing opened up.
Cables were fine, but, when checking the cable on a hard disc, it moved. The screws holding the hard disc in place created a pivot point.
I looks like my errors were due to the way a hard disc works; mechanically.

Platters in the discs spin, and an mechanical arm moves across the surface of the disc and read or write the surface magnetically. Think of how a vinyl record player works. However the arm should never touch the surface of the disc.
Now imaging this taking place on a see-saw. The arm reaches out, and tips the see-saw over. This is a problem. A sudden movement can cause the arm to touch the disc. The disc "parks". The arm swings back and the plates stop spinning for a while because the sudden motion is picked up as a failure condition. This is all done in the hardware, and requires a full de-powering to un-park. This is not a reboot. This is turn off the PC, and wait for a capacitor to discharge.
In the meantime, the operating system has suddenly lost, well, itself. Not everything in memory stays in memory. Stuff gets written to the hard disk so it can cope with new stuff. So the operating system looses it's memory. And Grocks.

I put in an extra screw to stop remove the pivot point... And the machine is now happy for hours on end.

This however means that I can do a few things at home. Namely write and review. I'll explain later.

However I need to get something like SpinRite to make sure there are no physical errors on the disc. Which should trigger another post.

Take care,
Will

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