The Importance of Terminology's Quality
martin at see.sig.for.address.invalid
Thu Aug 21 23:22:09 CEST 2008
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.
> 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 <rpw3 at rpw3.org>
> 627 26th Avenue <URL:http://rpw3.org/> San Mateo,
martin@ | Martin Gregorie
gregorie. | Essex, UK
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