CDROMs were the 'downloading' of the 80s and 90s.
I used to have a small collection of well-thumbed reference books that I take with me whatever was my current gig.
To be accurate the internet existed but we didn’t have the web resources, it was quite different.
We would also use BBS systems with forums as well as email to communicate with experts etc.
'Store and Forward' via UUCP was my norm around 1991.
I remember how our little group of UUCP nodes was so excited when one of our members sent an email from Australia to the States. (And received a reply back!! In only 10 minutes!! WOW!!)
I recently just gave away a bunch of my old reference books
I have had many cleanups of my reference books and magazines from the 80s-90s era. From about 50 shelf-feet to about 3 shelf-feet. On the other hand I have also re-bought some of those discarded reference books. And several other books are getting very tattered, but still used after 30-odd years.
I once wrote a program in assembler that was 7 bytes long (the executable was 7 bytes) to reset the graphics card.
It was great time to be a "programmer" in those days because you got to try so many different things instead of just cutting and pasting something from the internet. A lot of those things failed and you learn a lot from your failures.
I learned HTML/JS/CSS, Perl, PHP, Java, C, Linux, etc. all that way, with ebooks. Was a great time before Stackoverflow, when you really learned concepts, not looked for solutions :-)