In a message to Linda Proulx, Murray Lesser wrote re: Get an OS/2 guru


HS>This is a common belief, but wrong, at least for DOS and Win95. 
   >These 2 OS's do see all the primary partitions on a single hard
   >drive.  Your machine is living proof (at least for DOS).  I can't
   >swear to it, but I'm almost sure that OS/2 would also see them all.
 
ML>     Taken in context, the unattributed paragraph is entirely correct. As
ML> I remember the original, the topic being discussed was Boot Manager.  If
ML> all your bootable partitions are primary partitions on the same drive,
ML> they all have the same partition letter (usually C: on the first HD,
ML> since neither DOS nor Windows can boot from any other partition).  As a
ML> consequence, none of the booted systems can see any other bootable
ML> partition because you can have only one active C: drive on a system at a
ML> time.  (Your guru should have known this!)  With this exception, in
ML> general, OS/2 can see all primary partitions and extended partitions,
ML> but may not be able to read them.  OTOH, neither DOS nor Win95 can see
ML> partitions formatted HPFS, whether primary or extended.  This is not a
ML> valid reason not to use HPFS for big partitions; perhaps it is a valid
ML> reason not to boot DOS nor Win95 :-).

IIRC, newer versions of Windows (including NT) disregard the PC
standard of only allowing one primary partition to be visible at
a time.  Therefore Windows can see multiple primaries on a single
device.  Whether or not this is a good depends on your point of
view, I guess.  OS/2 has held to the standard of not seeing 
primary partitions that are not marked as active, so OS/2 will
not see your inactive primary partitions.  I believe the PARTFLT
driver can be used to work around this, if you really want to do
so.
 
HS>If you explain this to him, he'll no doubt ask how the heck (and
   >possibly why the heck) you created 4 primary partitions on one drive,
   >since FDISK will refuse to directly do this.  The answer to "how" is
   >that I used my bag of tricks - a combination of FDISK and Norton
   >Utilities.  "Why" is a much longer story.
 
ML>     Do not ever, ever, ever, use Norton Utilities (or any other
ML> DOS/Windows disk-fixer utility) on a partition (or drive) containing
ML> OS/2 files, UNLESS you are really an expert on the OS/2 internal file
ML> structures and know exactly what you are doing!!!
ML> 
ML>     At the worst, you will lose your desktop, which is mainly stored as
ML> OS/2 Extended Attributes.  The FAT file system used by OS/2 is "backward
ML> compatible" to that used by DOS/Windows to the extent that it can read
ML> DOS FAT files, but the reverse is not quite true.  OS/2 FAT uses two
ML> "reserved" bytes in the DOS FAT directory structure to point to the
ML> "attached" file that contains the Extended Attributes belonging to that
ML> "owning" file.  OS/2 also has a "dummy" file (EA DATA. FS) in the root
ML> directory of any FAT partition containing EAs, that is used to keep
ML> track of which portions of the physical file space on that partition
ML> hold EAs (this file is not normally displayed by an OS/2 FAT "DIR"
ML> command; "DIR /A" will display it).  DOS has no provisions to see this
ML> file (note the "illegal" file name).  A DOS "drive fixer" utility may
ML> wipe out all your EAs while "fixing" what it found to be a "corrupted"
ML> directory :-(.  At best, some DOS "defragger" utilities (that recognize
ML> OS/2's existence) don't wipe out the EA "files" but leave them where
ML> they were, rather than moving them to follow their "owner" files in
ML> physical sequence; thereby reducing performance when reading files
ML> containing EAs.  This would be especially noticeable when the system is
ML> loading a large REXX program.

And yet another reason *NOT* to install OS/2 to a FAT partition. 
HPFS has no need for cobble-jobs like "EA DATA. SF" to handle 
extended attributes.

ML>     Incidentally, IMO, it is very poor practice to install more primary
ML> partitions than are needed, because this unnecessarily limits
ML> flexibility for future changes.  

Yes, save the primary partitions for those inflexible systems 
that absolutely require them; ie, Microsoft operating systems 
and IBM's Boot Manager.


 * KWQ/2 1.2i * Internet: John.Thompson@attglobal.net


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