EDSAC as early as 1949 had an "initial orders" module. A boot-up ROM. There was a bank of rotary selector switches, to set the octal digits in each ROM word.
David Wheeler (of subroutine fame) figured out the most sensible thing to put in the tiny ROM was a paper tape loader and mini-assembler that loaded the rest of itself from paper tape. So at switch-on the machine would start reading the tape input and run. Programs could be written on the teletype with mnemonics and relative addresses in octal.
It seems a little strange that more advanced later machines like the original PDP-11 from 1970, couldn't "autostart" from ROM like that. You had to toggle in a bootloader.
I think that was because core memory was non-volatile. (EDSAC didn't use core; it had a refreshing DRAM-like delay line memory.) With core, you only had to toggle the bootloader into once and, provided your software didn't accidentally overwrite it, it was still there after a power cycle. So re-toggling in the boot loader was not really that common, despite how much lore surrounds it.
Yes that early pdp-11s had core memory, its contents survived power cycling. We'd hand toggle in the bootstrap into high ROM and start it, it would load whatever we were running from paper tape - unless you did something stupid that trashed that high memory you'd get to reuse the bootstrap over and over
Having said that the bootstrap was something like 8 16-bit instructions, a pain but not impossible
DonHopkins comment is marked dead but I’m glad I had show dead on because it’s right in the intersection of what I’m interested in, especially the forth on pdp-7 stuff. (The intersection is my interest in explanations of implementing forth from scratch and about the pdp-7 specifically.)
retrac · · focus · HN ↗
David Wheeler (of subroutine fame) figured out the most sensible thing to put in the tiny ROM was a paper tape loader and mini-assembler that loaded the rest of itself from paper tape. So at switch-on the machine would start reading the tape input and run. Programs could be written on the teletype with mnemonics and relative addresses in octal.
It seems a little strange that more advanced later machines like the original PDP-11 from 1970, couldn't "autostart" from ROM like that. You had to toggle in a bootloader.
I think that was because core memory was non-volatile. (EDSAC didn't use core; it had a refreshing DRAM-like delay line memory.) With core, you only had to toggle the bootloader into once and, provided your software didn't accidentally overwrite it, it was still there after a power cycle. So re-toggling in the boot loader was not really that common, despite how much lore surrounds it.
Taniwha · · focus · HN ↗
Having said that the bootstrap was something like 8 16-bit instructions, a pain but not impossible
drivers99 · · focus · HN ↗
justin66 · · focus · HN ↗