<> The first sector DOES NOT HAVE TO BE THE BOOT. < <Hi < It does on my system unless I toggle in a loader or have <EPROMs to do it. I'd like to not have any EPROMs if I don't <need it. The controller automatically loads track 0 sector 1. <I start executing at address zero and it boot loads the <CPM system. The boot loader then jumps to the start of <the CPM and it over writes info at address zero with what <it requires there. As far as I know, I am following the examples That is an example of the MDS800 style of boot. It is also fairly atypical of many. <for a non-MDS800 type system and following exactly what is <shown on 6-14/6-15 of the CPM manual that I got from the <unofficial site. The mapping shows that the first sector <is a cold start loader and the CPM ( CCP ) part doesn't start until <the second sector. Yes that config is specific to the MDS800 and that boot will likely NOT work with any controller in a IMSAI. If the controller in the imsai is the one I think it is (has an 8080 and an d372 FDC), the bios is simplified as that one does a lot of the work. I've built enough CPM system to have the configuration guide memorized. However I stopped going by the book as it's actually a bit to terse and does leave one to much imagination. The book by Andy Johnson-Laird The Programmers CPM Hand book is a must have for anyone doing bios work. Allison