Msdos hidden files viewable from linux?

[mikebw at bilow.bilow.uu.ids.net (Mike Bilow)]

Albert Cahalan wrote in a message to Mike Bilow:

 AC> Note that it is _impossible_ to correctly backup and restore
 AC> DOS system files without low-level disk access (read:
 AC> dangerous).  The system bit means that the file is sensitive
 AC> to it's physical position on disk.

The "system" bit does not imply this.  In fact, as of DOS 4.0, only
IO.SYS/IBMIO.COM was sensitive to physical location, and only the first cluster
of it.  MSDOS.SYS/IBMDOS.COM was also sensitive to physical location in DOS 3.3
and earlier.  COMMAND.COM has never been sensitive to physical location.

Worse, several DOS-based copy-protection schemes, such as Everlock, depend upon
storing information about the physical location of files which do not have the
"system" bit set or any other special marking present.  As a result, backing up
and restoring a program which uses the Everlock copy-protection scheme will
prevent it from working, one of the things which has contributed to its demise.

 AC> As far as I know, you
 AC> can't back up and restore /boot or the kernel either,
 AC> because lilo gets confused.  The same goes for msdos.sys and
 AC> io.sys.  Maybe someone could write a program to fix the boot
 AC> sector to point to these files.

DOS 4.0 and later actually works pefectly well if you clear the "hidden" and
"system" bits from IO.SYS and MSDOS.SYS.  You can even copy IO.SYS, MSDOS.SYS,
and COMMAND.COM to a blank floppy and it will be bootable, as long as IO.SYS
and MSDOS.SYS occupy the first two records of the root directory and IO.SYS
starts in the first logical cluster of data space.  The SYS.COM program makes
sure that these conditions hold in addition to just copying the files.
 
-- Mike