On Thu, 9 Nov 2023 at 17:48, Paul Gilmartin < 0000042bfe9c879d-dmarc-requ...@listserv.ua.edu> wrote:
> On Thu, 9 Nov 2023 16:18:17 -0600, Glenn Knickerbocker wrote: > > > >I've heard tales (probably at KTRU) of reading magnetic tape/cards with > iron filings and a loupe. > > > I believe I saw one. A flat container of ferrite slurry with a > transparent top > and a diamagnetic membrane bottom. Pressed against the tape, it clearly > showed record gaps. Reading the data would have been a challenge, > even at lowest density. > I have a can of that iron-filings-in-solvent from around 40 years ago. I havent played with it for a few years, but the solvent hadn't evaporated, and it still worked. It is indeed not feasible to read 1/2" mag tape even at 800 BPI, but what I was able to read with just a magnifying glass is the magstripe on old pre-chip credit cards. IIRC the stuff was made by (or at least branded) 3M, and was intended for (analogue) audio tape head alignment. IBM and STK CEs used it just to verify that there were data blocks, IBGs, and TMs, but not to try to read the actual data. It's a bit like looking at a CD (let alone DVD or Bluray) disk with an optical microscope. It looks about the same at almost any magnification - just shiny with colour fringes. You won't see the bits. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
