I'd prefer a year-by-year graph, something like (not necessarily the "demand", just "supply")...
Google found me that, which goes back to 2009, but I couldn't get it to cough up anything going back as far as 1969 (or even earlier).

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Re @GeraldEdgar's comment. Tapes, maybe: in 1969 the 6250bpi 9-track tapes were just becoming available, replacing 1600bpi (I still recall pressing Stop/Rewind/Unload and the subsequent vacuum column "whine"). So a 1200-foot tape would contain 11.25MB 8-bit bytes, or let's just say 100tapes/GB, or 50tapes/GB using 2400-foot tapes. And the typical datacenter might have a GB or so of disk, so I'd guess you're likely right that tape storage exceeded disk.

But a box of 2000 80-column cards, even if binary-punched, would store 160KB, whereby a GB requires 6250 boxes. And, wow, I don't recall ever seeing that many boxes of cards in one place (or maybe ever at all, for that matter).

I asked the question with respect to disk because of an off-the-cuff remark I made to a co-worker that my home-office disk capacity of ~75TB (mostly backups, six 10TB WD EasyStore's, a few 4TB 2.5" externals, plus about 10TB of internal disks) might well exceed the entire planet's disk capacity back in 1969, when I got my first computer job.

That conjecture was met with extreme skepticism. But I figured that at ~1GB/datacenter (which may well be an overestimate), and maybe ~35,000 datacenters worldwide in 1969, I might even have double the entire planet's disk capacity back then. (Note: I also couldn't google the number of datacenters in 1969, but seem to vaguely recall hearing something like ~35,000 back at that time).

    E d i t # 2

So, below's a figure I found at https://ethw.org/w/images/5/52/EPC_-_fig_6.jpg, which comes from an interesting historical article at https://ethw.org/Early_Popular_Computers,1950-_1970

The numbers seem roughly in line with my remark above about a "vague recollection" of 35,000 datacenters worldwide during the illustrated timeframe. And if we then also accept my perhaps-generous guesstimate of 1GBdisk/datacenter, then my home office disk capacity of 75TB pretty much equals the total planet's disk capacity circa 1968.

Of course, the predictable hockey-stick shape of this curve quickly overwhelmed my little boast. But it's still kind of interesting to contemplate, i.e., a mind-boggling way to illustrate how incredibly far and fast the technology has advanced. I could instead say that my desktop i7 is about a million times faster than the IBM 1620 I first programmed in the fall of 1966. And that's indeed impressive, but doesn't quite capture the imagination in the same way as saying my home office disk capacity equals the entire planet's disk capacity in that same year.

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    $\begingroup$ Perhaps, in 1969, storage on digital tape was still larger than storage on disk. We could also compare to storage on punched cards. $\endgroup$ – Gerald Edgar Dec 8 '19 at 13:41
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    $\begingroup$ my home-office disk capacity of ~75TB --- With this much invested in storage capability (I realize that probably not all of this storage is being used), hopefully you don't have all the backups in one place. If something is really important, I'd invest in bank safety deposit box so as to not lose your stuff in case of a tornado, a house fire, a bad earthquake, a hurricane, a bad gas explosion in your neighborhood, etc. Of course, there's also cloud storage, but if you've got this much stuff, I'd invest in more than home and cloud storage. $\endgroup$ – Dave L Renfro Dec 9 '19 at 12:45
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    $\begingroup$ Don't forget the TTY-generated paper punch tapes! $\endgroup$ – Carl Witthoft Dec 9 '19 at 13:08
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    $\begingroup$ I once worked in the IBM card warehouse of the California Department of Public Health, where there were several floors of shelves of cartons of IBM card boxes (10 boxes per carton, 2000 cards per box, = 2.4 MB per carton), leaving an impression like the computer room in Forbidden Planet or the final scene of Raiders of the Lost Ark. There must have been at least a GB there. $\endgroup$ – kimchi lover Dec 9 '19 at 13:40
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    $\begingroup$ @kimchilover ... Did I hear that punch cards were pioneered by the IRS for storage of its records? So maybe their card storage in/near D.C. were bigger than the California Department of Public Health. $\endgroup$ – Gerald Edgar Dec 9 '19 at 13:51

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