Michael Rowley wrote in a message to All:

 MR> Sorry to waist  some of your time, but if anyone out there has 
 MR> the patients, and the time :)  could someone try explaining to 
 MR> me why support for another file system could not be built into 
 MR> Dos?  I know there are drivers that will allow Dos to read HPFS 
 MR> for example, but what about allowing it to boot from an hpfs 
 MR> drive?  This would be increadibly handy.

HPFS uses a chained boot procedure.  The partition boot sector is loaded by
ROM and executed, which loads a special file named OS2BOOT.  This file
contains what is called the "Mini-Filesystem Driver," which
allows reading from the HPFS partition before the usual HPFS.IFS driver is
loaded.  OS2BOOT, in turn, loads OS2LDR, which loads OS2KRNL, which loads
the BASEDEVs and then the DEVICEs.  IFSs, such as HPFS.IFS, are loaded with
the DEVICEs.

In theory, you could get DOS to boot from HPFS using the same hooks that
allow DOS to boot from a DBLSPACE/DRVSPACE compressed volume.  However,
this would be a great deal of work and would require quite a lot of code
because of the complexity of HPFS.  Several operating systems other than
OS/2 can understand HPFS, including Linux which has a reverse-engineered
driver and Windows NT (in 3.51 and earlier) which was written by people who
had access to the OS/2 HPFS source code; NT itself was originally developed
on OS/2.
 
-- Mike


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