On Thu, 21 Aug 2008 09:11:48 -0500, Rob Warnock wrote: > You're assuming that all machines *have* some sort of "boot ROM". Before > the microprocessor days, that was certainly not always the case. The > "boot ROM", or other methods of booting a machine without manually > entering at least a small amount of "shoelace" code [enough the *load* > the real bootstrap], was a fairly late invention. > Quite. I never knew how to boot the Elliott 503 (never got closer to the console than the other side of a plate glass window). However, I dealt with that aspect of ICL 1900s. They had ferrite core memory and NO ROM. When you hit Start this cleared the memory and then pulsed a wire that wrote the bootstrap into memory and executed it. The wire wove through the cores and wrote 1 bits to the the right places to: - set word 8 (the PC) to 20 - set 25 words from 20 as bootstrap instructions to boot from disk.
Then it started the CPU running. On the 1902 this sequence often didn't work, so a good operator knew the 25 words by heart and would toggle them in on hand switches, set PC to 20 and hit the GO switch. > > -Rob > > p.s. Similarly, the DEC PDP-8 & PDP-11 were also originally booted by > manually toggling the console switches in order to deposit a few > instructions into memory, and then the starting address was toggled in > and "Start" was pushed. It was only later that a boot ROM became > available for the PDP-11 (as an expensive option!) -and only much later > still for the PDP-8 series (e.g., the MI8E for the PDP-8/E). > > ----- > Rob Warnock <[EMAIL PROTECTED]> > 627 26th Avenue <URL:http://rpw3.org/> San Mateo, CA 94403 > (650)572-2607 -- martin@ | Martin Gregorie gregorie. | Essex, UK org | -- http://mail.python.org/mailman/listinfo/python-list
