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I was thinking about how Williams Tubes worked and how one could hypothetically "snapshot" (quite literally!) the state of a computer's memory by simply taking a photograph of the phosphor end of a memory-CRT - then feeding the stored state back into the machine by pointing a TV camera at the photograph and having the CRT display from the camera for a single refresh cycle before reconnecting back to the computer for state to be persisted on the CRT.

I imagine the technique could be used for any other computer that featured a visual display of its memory-state by way of der blinkenlights - this would assume that all its memory is visible this way. If a photograph of this was taken then a kind-of fax-machine could "scan" a photograph and use that to re-set memory would avoid the trouble of manually flipping switches to bootstrap a computer - I understand this is all within the realm of 1950s/1960s-era technology.

I know magnetic-tape and punch-cards predate computers and were used to store data (including bootstrapping) they share a considerable disadvantage: they cannot capture machine memory state in a "snapshot": they require memory to be streamed out first, thus freezing the machine's execution until all data had been written. They also suffer from relatively poor data density: a punch card requires about 2x5mm (10mm^2) area for each bit, while 1950s magnetic tape (e.g. UNISERVO) could store 128 bits/inch (0.19mm per bit) albiet in one dimension. Whereas photographic film is theoretically capable of much higher resolutions (thinking about microfiche, for example).

So, were photographs ever used to store memory state?

  • 5
    Not exactly what you are asking about, but microfilm is a photographic technique used for data storage. – RonJohn Apr 26 '18 at 10:59
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    The Williams Tube (at least the refresh cycle where it scans TV-like over the tube) would produce a signal that could very well be directly used for Fax-like transmission, and reception. The random access memory part of the functionality would be problematic: when you have dots and dashes representing 1 and 0 , the re-translation of a photographic copy might prove hard. --- the data was not in the dots and dashes, after all, but in the electric charge produced by them. – bukwyrm Apr 26 '18 at 11:32
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Yes, the IBM 1360 used it. The wikipedia page suggests that it could store 0.5 terabits of information.

https://en.wikipedia.org/wiki/IBM_1360

Fascinating design.

  • Indeed: an example of Big Blue at their most omnipotent, working on giant government contracts. And even they ended up with a solution they couldn't market … Interestingly, the cells and error correction method look strikingly like QR Codes. – scruss Apr 26 '18 at 14:59
  • @scruss I couldn't find any detailed photos of an IBM 1360 cell - do you have examples we can look at? – Dai May 1 '18 at 20:03
  • the image on wikipedia, along with a mention that it used error correction to allow recovering if parts of the cells were damaged. To me, that's basically a QR-code – scruss May 2 '18 at 1:04
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It IS used in at least two places even today:

  • QR codes. There is the possibility of the print media carrying it having been prepared involving photographic methods.

  • Digital sound in movie theaters, when projecting from actual film - even quite modern standards like Sony SDDS, Dolby Digital define how the sound can be carried as digital data encoded optically in an off-screen area of the film strip.

5

Sprocket-driven 35 mm photographic film stock was used to store data in the British Elliott 803 computer. It wasn't used optically, however: it was coated with iron oxide and used as magnetic media.

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    (Used) 35mm film was also used for the first Zuse machines as punch tape :)) – Raffzahn Apr 26 '18 at 1:52
  • There was also "optical paper", that was going to be the next big thing in storage in 1988-1989. While not strictly a film, it was an optical media. It, and the perhaps similar FMD-ROM of a few years later, went nowhere. – scruss Apr 26 '18 at 15:07
  • Early rockets would use a pin hole over strips of 35mm film for telemetry storage. – jwzumwalt May 2 '18 at 1:38
  • … although those were for monitoring radiation and used as photographic records rather than digital data – scruss May 2 '18 at 14:03
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There were many optical readers used for punched paper tape; so in some sense holes in paper was treated as a photographic record of the dots on the screen. The Colossus machine at Bletchley Park used optical tape readers at very high speed and this pre-dated the Williams Tube.

https://youtu.be/xeDyF4HviDE

3

Not exactly what you expect, but the Zuse Z1 and its successors used photographic film as punched tape. This design decision was made because Konrad Zuse was able to find large amounts of old film rolls on a nearby scrapyard, removing the need to make his own tape.

2

Yes, of course photographic film was used for data storage, but not necessarily computer data storage. A seismometry network has dozens of stations reporting to a central site, and it used to be (deades ago) common to see a Honeywell Visicorder (aka drippy-corder) in such an installation, slowly reeling out 35mm film through a dark chamber where signals are recorded with galvanometer (mirror/beam) or CRT onto the film, which continually advances and dips into developer, stop bath, and fixer, making a continuous record for days between reel changes.

About ten channels (with circa +/- 1mm deflection) fit handily onto the 24mm clear space between sprocket holes of 35mm movie film. Other 'Visicorder' models used other (paper) recording techniques.

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