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I built my first computer in early 1979 from a kit - as in, I soldered all of the components onto the motherboard, hacked a cassette tape player as the storage drive, and hacked a B&W TV to be able to use it as a monitor. (TVs didn't have HDMI / VGA plugs in those days!) The kit cost me well over $1,000 (in 1979 dollars).
It used a Z80 processor, and I splurged on the RAM to get the "huge" 16 kB upgrade instead of the basic 8 kB RAM. (That's KILObytes of RAM, not megabytes or gigabytes!)
The first time you booted it, you had to laboriously enter a bootstrap program in binary machine code, line-by-line, by flicking 16 switches on the front panel, load the 16 bits into RAM, then repeat until you had loaded all of the initialisation commands. Get any one of those 16-bit commands wrong, and you had to power down and repeat until you got a successful boot. Then the first thing you did was write the bootstrap code to a cassette tape, so that you could reboot from the cassette drive.
At this point, you could use the keyboard (also soldered from a bag full of components), but there was no Disk Operating System or programming interface as we think of it today - the only way of issuing commands was in machine language, so the next thing you did was to set about loading a BASIC Interpreter using line-by-line machine-language entry from the keyboard. This took MUCH longer than loading the bootstrap program the first time, but at least you could now save your work progressively onto tape, and pick up from where you left off. From memory, it took me a couple of weeks from first boot before I could actually USE it for something!
I then wrote a structural analysis program in BASIC from scratch (using the theory I had learnt in 3rd-year university), and used it during my final year of studying Engineering at university.
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