Back in '78 or so, my first computer was a hand-assembled Nascom I (2MHz Z80)[0] with 1kb of RAM. No assemblers, no disk drives, not even a cassette tape. Just a keyboard and a simple ROM that let you load hex values in memory. The low-res video display was memory-mapped, so after much study of circuit diagrams,the Mostek Z80 manual and the ROM I got to understand memory addressing, where the screen was and how the hardware worked. So my first Z80 program was just 3 instructions entered as hex opcodes; all it did was splat an asterisk on the screen but what a buzz I got at the time :)
ld a,2a # Load ASCII '*' in to acc
ld hl,d80 # Set HL to point to video-mapped RAM
ld (hl),a # Put character on screen.
Some years later I wrote one of the first multi-user games, picked up by British Telecom to run on their Prestel/Micronet network. By that time I've graduated to 4MHz Z80s, with home-made 2MB RAM disks and 256Kb of main RAM accessed with a crude TTL MMU; we got up to 64 users per Z80, albeit accessing the system via 1200/75 baud modems.
[0] It graced the cover of Issue #1 of Personal Computer World; I still have a copy.
We should have a site where these experiences are retained.
My teen years were in the 80s and I was mad about the Z80 in my cheap Laser 200 but was too isolated to have access to much information and equipment.
Yet, I reversed engineered the schematic of my little, made my own memory expansion (I couldn't afford the official one) out of stacked SRAM chips, mapped the ROM, build my own crude tools to see what was going on in the hardware, coded assembler by hand and poked the memory to store the programs, one byte at a time...
It taught me about electronics, fundamentals of gate logic and how microprocessors worked, programming (and no I wasn't ruined by BASIC), and those constant discoveries drove me to want to know more.
It was such a formative and fun experience for a curious teen to explore something in depth -with no help other than a few magazine and books- and uncovering the layers of what made a computer tick, however minimal that computer was.
[0] It graced the cover of Issue #1 of Personal Computer World; I still have a copy.