Rebirth of IMSAI - test-drb@ccmp.vtda.org

31 Mar 1999

That sort of thing was common.  I never figured out why they didn't just
load the code into RAM from the ROM, then make the ROM go away.  Eventually,
that was the method of choice.

Dick
-----Original Message-----
From: Allison J Parent &lt;allisonp(a)world.std.com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Tuesday, March 30, 1999 5:05 PM
Subject: Re: Rebirth of IMSAI

...
 <I said 'ROM' because on a number of
machines, it was just a few TTL chips
<that gated C3, lobyte, hibyte onto the data bus on the first 3 fetches
<after reset.

Most used a mux and jumpers to fake a 3byte rom with the first byte
hardwired as C3h (jmp in 8080/8085/z80) and it was jammed on the bus for
boot and only then.  another approach was to on power up map rom to loc 000
and also F800h and then disable the mapping after the code was running up
high.   Plenty of tricks to fake that.

Allison