Date: Tue, 20 Mar 2001 10:02:11 -0600 From: Rob McGee To: opendos AT delorie DOT com Subject: Re: DOS drive letter assignments Message-ID: <20010320100211.A24606@sl7> References: <20010320042804 DOT B24471 AT sl7> <3AB76F09 DOT FA6C75EC AT seltek DOT com DOT au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.2i In-Reply-To: <3AB76F09.FA6C75EC@seltek.com.au>; from csouter@seltek.com.au on Wed, Mar 21, 2001 at 12:54:01AM +1000 Sender: ws AT room101 DOT 2y DOT net Reply-To: opendos AT delorie DOT com Errors-To: nobody AT delorie DOT com X-Mailing-List: opendos AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk 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