People like me never have to poke around to find anything. Everything is either answered by a Youtube video or Stackoverflow, but it only gives a surface level understanding of everything, and we become clueless when something breaks.
They included circuit diagrams, data sheets for individual chips, just about every detail of how the system worked.
You'd still have to figure out a lot just to understand those reference manuals, and guess a lot, especially with no internet and no good library (my local library did not have books like this!).
I only had a very small number of books. But I did have the Advanced Guide. Having so much detail available in reference manuals was great for a young mind!
Also when I was like 7-8 (edit: previously wrote 10) I was given the Ladybird book for young children: "The Computer (How It Works)".[1] A tiny book. In retrospect I learned a lot of great grounding from that book even though I hadn't yet seen an actual computer. I guess it gave me an appreciation for the video games I played with on show in the supermarket, and the pictures of minicomputers and microcomputers I saw in hand-me-down computer magazines.
[1] https://www.amazon.co.uk/Computer-Ladybird-How-Works/dp/0721...
I'm occasionally asked, by people who find learning this stuff frustrating, where did I learn about logic circuits, where did I learn about assembly, where did I learn about RAM and ROM, etc. and for a long time I couldn't put my finger on it. I think it started with being exposed to that book and some early computer magazines at a young age, without even seeing or touching a real machine for a year or so afterwards.
Edit: wrongola! Turns out, the last machine I worked with that had a real manual was either a MicroVAX, or a PDP-11, both of which I used in college. Writing ASM for the PDP-11 was great! I just wish I was better at program then, lol. :)
http://users.telenet.be/kim1-6502/6502/2ksa/2ksa.html
> "Cover: Schematics for a 5V, 3A regulated power supply and a 1K x 8 read/write memory block. The power supply and three such memory blocks can be added to the basic KIM-l microcomputer to provide the 4K RAM required by this assembler. Parts are available from Jameco Electronics."
https://www.youtube.com/user/MrCarlsonsLab https://www.youtube.com/user/gradyhillhouse
Also for history students Mike Duncans Revolutions is amazing