[GTALUG] War Story: Asus UX305ca SSD failures

[Russell Reiter]

On Fri, Aug 2, 2019, 8:49 AM James Knott via talk, <talk at gtalug.org> wrote:

> On 2019-08-02 08:03 AM, Russell Reiter via talk wrote:
> >
> >     > - 9-track mag tape: 10 years
> >
> >
> > Would this form factor be sized like commercial 8 track audio tape
> > with an extra track squeezed in for sync?
>
> No, it was 1/2" tape on an open reel.  And it was 9 or 7 actual tracks,
> with one track used for the parity bit.  They used odd parity, to
> guaranty at least one "1" bit, to provide clocking for the NRZI encoding
> used.
>
> https://en.wikipedia.org/wiki/Non-return-to-zero


Interesting. In audio recording synchronization, one track is usually a
click track.  Not necessarily tic tic tic but rather tic tok etc. This
helps the listener who is overdubbing another instrument to centre to the
beat more accurately.

The interval between the tic and the toc sets the logical state of the
beat, tic being the leading edge of the beat and toc the trailing edge.

I read that in RLL over serial UART reception, the receiver is often
clocked at a higher rate (than the bus clock? ) in order to garner a
broader validated baseline of leading and trailing signal edge.

>From your link, NRZ may map to the trailing edge of the signal but not
necessarily, as there are several other validation methods for non clocked
signals.

Also interesting is that NRZI  seems to have two definitions. Non Return
Zero Inverted or NRZ-IBM.

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>


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