william_b_noble wrote:
aaah, my first machine at home was a PDP8-S with 1K of 13 bit core memory -
it was non-volatile, but certainly not ROM - and it had front panel switches
for loading a bootstrap program

I still have a working PDP 8/L in the garage.


"Dave Martindale" wrote in message
...

John Ings writes:


I go back further than that. My first computer was a homebrew that
used an 8008, and yes, bootstraps were loaded via front panel
switches. ROM? What's that?

On the PDP-11/45 where I first used Unix, the ROM was a board with a
whole lot of diodes soldered to it. I think there were 512, for 32
words of 16 bits. As received from the factory, the ROM was all zeros.
You clipped out diodes to get one bits in whatever position you needed
them

We got bootloaders for hard disk, tape, and floppy in that 32 words.

But we used the machine for a year or two without the ROM. It wasn't
that bad. You just loaded the disk controller address into the
switches, then deposited a length and a read command into the disk
controller registers, and your boot block was magically at location zero
in memory.

(This only worked because the 11/45 bus sequencer continued running
when the CPU was halted. On other PDP-11s you had to put the CPU into
an infinite loop to make DMA transfers happen).

Dave