Recovering the ROM of an IBM 5100 using OCR (among other things)

[Warner Losh]

On Thu, Jun 27, 2019 at 8:42 AM Kevin McQuiggin via cctalk <
cctalk at classiccmp.org> wrote:

> In the early days of cyber crime (it was called “computer crime” back in
> the 1980s), fraudsters would purchase an aerosol spray with tiny metal
> particles in it (I forget what the specific valid use case was, but it was
> legitimate), and apply the spray to the mag stripe on the back of credit
> cards, then visually read out the bits with a magnifier.  1s and 0s
> oriented the tiny metal bits orthogonally, and this could be observed.
> Then they would program card blanks with the recovered mag stripe data.
>
> Mag stripe readers were expensive and hard to acquire in those days, so
> this was the chosen method of recovering track data from credit cards.
>

Back when I got to school and I was hanging around the computer room on
campus (back when it was THE room on campus with computers), I saw this
half-dollar sized plastic fob on the desk and asked what it was for. The
on-staff operator took a mag tape off the rack, opened it up and set the
end of the tape on the table. She then took the fob and placed it on the
end of the tape and all the iron filings that were suspended in the liquid
inside the fob aligned to the magnetic fields of the tape. They used it to
tell the difference between 800, 1600 and 6250 bps tapes so they could
handle the tapes correctly (can't recall if there were two tape drives, or
if there were manual switches). I asked how she knew the difference, and
she said that after you do enough of them, you can tell by a glance. When
she started, her boss had given her a bunch of segments of tape of known
density to look at. After playing with it for a few minutes, and sometimes
referring back to them, she got the hang of it, which sounds a bit like
part of the story posted earlier in this thread.

I've also heard people tell stories of using this fob to find the end of
the marks and records on mag tape to splice together tapes that had become
broken and ruined (so they'd cut the damaged records out at record
boundaries to recover at least some of the data on ANSI formatted tapes). I
don't know if this was a tall tale designed to impress over a beer, or the
sad confessions of someone that had gone through a lot of pain and needed
to share...

Warner