[GTALUG] War Story: Asus UX305ca SSD failures

[James Knott]

On 2019-08-04 08:09 AM, Russell Reiter wrote:
> Also interesting is that NRZI  seems to have two definitions. Non
> Return Zero Inverted or NRZ-IBM. 
>

NRZI was created by IBM, specifically for use with tape drives.  They
were one of the earliest, if not earliest to use mag tape.  I read the
technical reason for "inverted" many years ago, but I have forgotten the
details.  Often that sort of thing is done to obtain best performance
from something.  One such example was the use of odd parity.  From a
strictly error detection point of view odd or even will work, but with
odd, there will always be one "1" bit for clocking, as I mentioned.

> Some nice pictures of an IBM unit in this link to a manual, for any
> other creative anachronists. 
>
> http://ibm-14In .info/223-6988-729-MagTapeCE-InstRef-62-r.pdf
> <http://ibm-1401.info/223-6988-729-MagTapeCE-InstRef-62-r.pdf>
>

I used to work on drives that looked similar.  However, they were made
by a company called Potter, but had the Collins branding on them.