Xerox 820 system disks in Teledisk format?

js at js at
Sat May 9 10:24:42 CDT 2009

dwight elvey wrote:
>  The reason for the FM on the fist track was that it
> was then compatable with boot code for disk that
> were all FM. One could boot FM and then switch to
> MFM for the rest of the disk. It seems strange now
> but made sense at the time.
> Dwight
True, but that's not all.   The reason for FM on T0 is so that any disk 
of any format that had been properly sysgen'd and contained the proper 
CBIOS could then be booted from that system.  It allowed the flexibility 
of having a multi-format system.  Another reason is so that the disk 
controller boot rom (or boot code wherever it was) could start booting 
ANY disk since they all began with FM 26x128.  Boot in FM, read the boot 
loader.  THEN, the boot loader which could be more complex and would 
specifically match that individual floppy (unlike the boot rom), it 
would continue the boot, handling whatever format the rest of the disk was.


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