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Old 5th May 2019, 12:28 am   #15
JohnBHanson
Heptode
 
Join Date: Aug 2009
Location: Worthing, Sussex, UK.
Posts: 661
Default Re: Gemini 80-Bus System

booting process varies between machines - but most do the following

1. The boot rom initialises the floppy disk controller sets the stepping speed and does a recalibrate to move the head of floppy a: to track 0. Actually for most systems with 80 track drives two recalibrates are required as the disk controller will only step out 77 tracks.

2. Next the boot rom does a read of side 0, track 0 and the first sector (numbered 0 or 1) to some address in ram.

3. The boot rom passes control to this first sector by jumping to an address within the copy of the first sector in ram. This then loads CP/M (at least the BIOS and sometimes the whole CPM image). Control is then passed to the cold boot vector in CP/M

4. The cold boot routine reads any remaining parts of CP/M the were not read by the first sector loader and jumps to the command processor.

There are variations - sometimes the first sector reads the entire CP/M image and sometimes the bootrom does. Other variations are even stranger.
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