A 16k Ram-Pack for the ZX81 used to be about £50, IIRC, back in the day. It plugged into an edge connector on the back and if, after a couple of hours programming, a butterfly came and breathed on it, then the whole thing froze and you had to start again........
Vintage Computing!
- Thread starter ninebob
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Hence in Red Dwarf, Kryton's immortal line "Starbug has crashed more times than a ZX81!!!" 
Some guys on my course built a Z80-based computer on a breadboard (seriously, not a PCB, a breadboard!), which they programmed with an array of dip-switches and a button. They would set the dip-switches to represent a binary value for a machine-code command, then press the button to load that command to memory. They would then set the switches to the next command, press the button and so on. There was no non-volatile memory to save the program onto, so they would reenter it at the beginning of every session.
It would take them an hour or so to enter their fairly simple program... provided no-one walked past their bench in the lab! ZX81-syndrome.
Some guys on my course built a Z80-based computer on a breadboard (seriously, not a PCB, a breadboard!), which they programmed with an array of dip-switches and a button. They would set the dip-switches to represent a binary value for a machine-code command, then press the button to load that command to memory. They would then set the switches to the next command, press the button and so on. There was no non-volatile memory to save the program onto, so they would reenter it at the beginning of every session.
It would take them an hour or so to enter their fairly simple program... provided no-one walked past their bench in the lab! ZX81-syndrome.
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