I got a response to the letter I wrote the Birmingham science musuem. This is what Jeff Smith, director of IMAX theater operations has to say:
Lamar has just passed your message along about the stats presented in the IMAX Theater Pre-Show. I have to agree with your comments, but have never changed the show since this is the way it was originally produced, but having talked with the creator of the show over the years, I have learned his methodology for the 24,000 CD-ROMs of information statistic.
According to him, if you take the average 74-minute CD-ROM at 650MB of data, and multiply it out, that would result in nearly 15TB of data for the image portion of a film.
Going backwards, assuming a 45 minute film, that would be ~241MB per frame (at 24fps.)
There is actually an active argument in the IMAX industry over the past few years concerning what type of resolution you need to achieve the quality of an IMAX 15/70 film presentation. An IMAX VP has said that it is the equivalent of a 105 megapixel image. While I think this might be a bit overkill, I've seen 8k images output, and that is far too low compared to the image quality of the film.
Hopefully this helps explain our usage of units a little.
In other words, it would take 24,000 CD-ROMS to store a 90 minute IMAX film as a sequence of uncompressed, 105 MB images.