6 ms·

Just for the record, and for those not familiar with these, the original ZX80 and ZX81's had only 1 Kb memory. The "expansion" to 16 Kb (and later to a whoppin

by jaclaz 10y ago

Just for the record, and for those not familiar with these, the original ZX80 and ZX81's had only 1 Kb memory. The "expansion" to 16 Kb (and later to a whopping 64 Kb!) was an extremely costly "add on", it was a small "vertical box" attached to the rear end connector (and the connection was - to say the least - flaky): http://www.computinghistory.org.uk/det/34163/ZX81-16K-Byte-RAM-Pack/ http://www.computinghistory.org.uk/det/34163/ZX81-16K-Byte-R... An image of a ZX81 with the expansion box mounted is here: http://oldcomputers.net/zx81.html http://oldcomputers.net/zx81.html

Joyfield 10y ago
That would be kB (kilobyte) and not kb (kilobit) or Kb (kelvinbit).
- quirkafleeg 10y ago
  What's a "kelvinbit"?
  - Joyfield 10y ago
    Exactly. ;)
  - WorldMaker 10y ago
    Now I want to see someone derive a nice formula that results in a kelvinbit. Offhand, I'd guess something to do with information entropy in temperature sensitive media. (Entropy rather than density as that would be more along the lines of bits/kelvin I'd assume. Or heat output would be kelvins/bit.)
- jaclaz 10y ago
  Yes, actually to be strict it would be kibibytes, KiB. But in 1980/1981 kibibytes didn't exist, all we had was good ol' fat Kilobytes made out of 1024 bytes, and WE LIKED IT. https://tinyapps.org/blog/misc/200702250700_why_in_my_day.html https://tinyapps.org/blog/misc/200702250700_why_in_my_day.ht...
osullivj 10y ago
Thanks for the pic. I had a 16K expansion pack for my ZX81, but it was third party, so a little cheaper than the official Sinclair product. Perhaps 30GBP rather than 50? I remember there being much chat at the time about the dreaded "RAM pack wobble". The ZX81 keyboard claimed to be touch sensitive, but was really thump sensitive! This could easily jiggle the bus connection from the motherboard to the RAM pack, causing the ZX to crash, possibly losing hours of work before it could be saved to tape. For me the solution was yet another third party peripheral: a real keyboard.
- bewo001 10y ago
  Static electricity was also a problem. Touching the ZX81 after walking over a carpet in winter resulted often in a crash.

by jaclaz 10y ago

Joyfield 10y ago

That would be kB (kilobyte) and not kb (kilobit) or Kb (kelvinbit).

quirkafleeg 10y ago
What's a "kelvinbit"?
- Joyfield 10y ago
  Exactly. ;)
- WorldMaker 10y ago
  Now I want to see someone derive a nice formula that results in a kelvinbit. Offhand, I'd guess something to do with information entropy in temperature sensitive media. (Entropy rather than density as that would be more along the lines of bits/kelvin I'd assume. Or heat output would be kelvins/bit.)
jaclaz 10y ago
Yes, actually to be strict it would be kibibytes, KiB. But in 1980/1981 kibibytes didn't exist, all we had was good ol' fat Kilobytes made out of 1024 bytes, and WE LIKED IT. https://tinyapps.org/blog/misc/200702250700_why_in_my_day.html https://tinyapps.org/blog/misc/200702250700_why_in_my_day.ht...

osullivj 10y ago

Thanks for the pic. I had a 16K expansion pack for my ZX81, but it was third party, so a little cheaper than the official Sinclair product. Perhaps 30GBP rather than 50? I remember there being much chat at the time about the dreaded "RAM pack wobble". The ZX81 keyboard claimed to be touch sensitive, but was really thump sensitive! This could easily jiggle the bus connection from the motherboard to the RAM pack, causing the ZX to crash, possibly losing hours of work before it could be saved to tape. For me the solution was yet another third party peripheral: a real keyboard.

bewo001 10y ago
Static electricity was also a problem. Touching the ZX81 after walking over a carpet in winter resulted often in a crash.