Re: Naive User Stories

Steve Harris [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
> If all the bits are magnetized in the same direction, the whole disk
> has a net magnetic field.  Yes, it's got a N and S pole, but that
> doesn't mean it doesn't interact with the earth's field.

Nitpick:  Disks don't work like that.  Read heads detect *transitions*.
No disk will ever have a significant net magnetic dipole.  Not even if
it's been put through a bulk eraser, as those use damped AC.  Maybe if
it was put in an MRI machine, it will.

There are subtler effects, however.  In princple you can get kT ln 2
joules of useful energy by randomizing a bit that starts out in a
known state.  And of course energy has mass.  So perhaps a blank
diskette, or one that contains the digits of pi or some other
determinate pattern, weighs slightly more than one that contains
random data.

Except that that's a measure of *usable* energy, not total energy.
*Unusable* energy weighs the same.  Too bad.  I was hoping we could
determine whether pi is truly random by placing diskettes on balance
scales.  Oh well.
-- 
Keith F. Lynch - [EMAIL PROTECTED] - http://keithlynch.net/
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