Mail Archives: opendos/2001/03/20/11:00:08
I appreciate your reply, Christopher. Thank you for the PartitionMagic
excerpts too. I have cut out most of your comments in this reply, which
I hope will not be confusing. I think, too, that I have replied to the
PQ text as well as to you, so I indicated where this may have occurred.
On Wed, Mar 21, 2001 at 12:54:01AM +1000, Christopher E. Souter wrote:
> I am assuming two physical drives here, and that the first primary
> partition on the first physical drive is currently the active
> partition, and that all partitions are formatted for FAT16 (both
> DOS and OS/2 can see them all), and DOS is installed on the first
> primary partition, whilst OS/2 is installed on the second primary
> partition. The Boot Manager partition enables the user to choose
> which OS to boot at startup time. Boot Manager is a primary
What I would like to do is leave Boot Manager out. Suppose for some odd
reason you're not using some trick to multi-boot. That second primary
partition on the primary master device would get letter "D" before the
search goes to other physical devices, correct?
The text you quoted from PowerQuest (before my initial post I tried
consulting their Web site for this, too, but came up with nothing there)
seems to say that only the first recognized primary partition per device
gets the drive letter. That implies that subsequent primary partitions
would get letters along with the logical partitions. But it does not
specifically say so.
The problem here is that DOS was designed with an assumption that you
would not have multiple primary partitions, at least not recognizable by
DOS. MS fdisk won't let you create a second primary partition. But other
tools like Linux fdisk and PartitionMagic can do it, and AFAIK most DOS
versions will work with and use those partitions.
> (Please note that you can only have a maximum of four physical IDE
> devices attached to an IBM-Compatible PC. Two can be attached to
> the primary controller, and two to the secondary controller).
Right, and this points to another of my unanswered questions: which
physical device gets drive letters first: the primary slave or the
secondary master? We know the primary master is first and the secondary
slave comes last. But what's the order in the middle? :)
> NOTE: As far as I know, there is no PC-compatible OS that can be
> ---- booted from a primary partition on an IDE device attached to
> the secondary controller. This means that all bootable
> partitions must reside on one or other of the first two IDE
> devices on your system. In the case of DOS, the bootable
> partition MUST be on the first IDE device. As far as SCSI
I think this is really a BIOS limitation. On one system I have here, a
Linux /boot partition lives as partition 4 in the last few MB on the
primary master. The root filesystem is on the secondary master (which is
not configured in the BIOS at all because the BIOS is out-of-date and
the drive is too big.)
I believe I once saw a BIOS which let you specify other drives as the
boot device. In fact I think it might be that way on the aforementioned
system, but I am not at liberty to reboot it and find out. :) I do know
that it can boot from SCSI, even with IDE drives present.
PQ> Next, all logical partitions with a file system that the OS
PQ> recognises are assigned drive letters, starting with those on the
One thing I did discover on my own was that the key for DOS is not the
filesystem per se, it is the partition type. I created a FAT fs on a
Linux native (type 82) partition. Linux used it as vfat, but DOS didn't
see it there at all until I went back and changed the partition type.
Similarly, if a DOS-recognized partition type holds a non-DOS filesystem
then DOS will just think it's unformatted. Unformatted media can have a
drive letter. (You have to have a drive letter to use format.com.)
PQ> Finally, CD-ROM drives and other types of removable media drives
PQ> are assigned a drive letter.
This isn't quite true. If your Zip is IDE or ATAPI and the media is
present at boot time, its partitions will be assigned drive letters
along with the real hard drives. The same is true for SCSI removables
like Zip and Jaz, *if* the SCSI adapter has a BIOS. The distinction is
whether or not a *software driver* needs to be loaded for the device by
the OS, as opposed to BIOS recognition.
> I hope that this might, at least partially, answer your question.
Thank you for the reply, and as above, it might. :) But there are still
some gaps and doubts. It is an interesting matter.
Rob - /dev/rob0
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