Back in the early '80s I built a kit computer (Compukit UK101), a 6502 based machine with 4K of RAM and BASIC in ROM.
I took the circuit for the UHF output and made my own 6809 based system initially with 4K of RAM and a simple IO board that talked to a 7 segment 8 digit calculator display.
That machine grew to four double Euro sized breadboard with 64K of dynamic RAM, a simple video controller based on the 6545 chip and a floppy disk board based on Western Digital chips.
All done by contacting manufacturers by post and asking for datasheets as a student.
I ran a commercial OS called FLEX/09 (much like CP/M). I had a language called PL/9, a one pass 6809 compiler that was C like but much simpler. Barely any runtime, squeezed to fit into 48K of RAM - an editor and compiler. I wrote my floppy disk formatter with it.
It all died when the wire wrapped wires turned black and the system stopped booting. By then I’d moved onto BBC machines - Electron, Master and Archimedes (ARM based). Eventually I bought a 486-DX2 50MHz - a machine I still have but no idea if it will still even switch on.
Having a hardware background got me a job working for an audio company doing device drivers and eventually a job in audio working for Codemasters, my first games company.
I wrote to Texas Instruments and they sent me back a paperback book describing every TTL chip from 7400 upwards. I read it cover to cover and learned quite a bit about TTL logic back then. I used TTL as the glue logic getting everything going, as well as 68xx and 65xx series chips to cover all sorts, like ACIAs, PIOs and video controlllers.
The internet did not exist back then. Even though I worked for a large American computer company with their own private network (text only), still no internet as such. It was called books and libraries back then. Oh… and no Amazon either.