On Fri, 24 Sep 2004, Rick Moen wrote:

> That is correct.  SYS.COM copies several files (io.sys, command.com,
> msdos.sys, and at least one other that I've mercifully forgotten about)
> with the read-only, hidden, and system flags set, to the indicated FAT
> filesystem.  One of those gets written to a specific physical location
> so as to be findable by the Int13h boot service, early in the boot
> process
[snip]

Starting at some DOS version, the physical location thing became no longer
necessary.  I'm not sure which version but somewhere around DOS 4-ish.
Apparently the DOS bootstrap code became smarter and figured out ways to
search for those files in the FS.  As a consequence, the "system" flag on
those system files (which tells the OS and utility tools like Norton and
PC Tools not to move those files from their physical location) no longer
became necessary as they were before.

To re-install the MBR, another important component for booting DOS and
Windows, uses FDISK's *undocumented* flag:

  FDISK /MBR

Once I told someone to do that over the phone and he freaked out (because
"FDISK is dangerous!")  I'm not sure if he had the guts to go through with
it...

-Mark


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Mark K. Kim
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