30 Jul
2007
30 Jul
'07
9:13 p.m.
On 7/30/07, dwight elvey <dkelvey at hotmail.com> wrote:
An alternative to switches is a diode ROM. You
don't need too many
diodes if the system already has some ROM boot code and all you need
is a call routine.
In the PDP world, there were diode bootstraps and rope-core
bootstraps. Most DMA devices were smart enough on their own to easily
load block zero into core at 0000 with little effort. I recall a
PDP-11 bootstrap that depended on human reaction time being slower
than the disk that could boot an RK06/7 in, essentially one word. You
stuffed the right value into the CSR directly, then jumped to 0000000.
Before you could type G 0000000 or whatever, the disk pulsed and the
block loaded, leaving you a boot block to jump into. The full and
proper auto-boot code wasn't even a dozen words anyway.
OTOH, a TU58 boot on a PDP-11 or a TD8E boot on a PDP-8 is a much more
involved thing to toggle in, but at least with a PDP-11 w/console ODT,
one can have a smart host toggle that in for you (as if it were a
human typing in the boot code one word at a time).
-ethan