Drive letters shifted when I add a 2nd HD w/1 logical partition. Why?

[jaclaz]

@Ponch

With all due respect, maybe jcarle is the only person knowing what he meant.

I don't think that the fact that this is an old thread is at all relevant, as long as more CORRECT information is given.

@all

As is, the sentence:

FAT was designed to have a single primary partition and a single extended partition.

does not stand, as eidenk pointed out, if I may with a bit of unneeded aggressiveness, as FAT is a filesystem, and "knows nothing" itself about other partitions, a FAT partition doe not evem "know" if it is Active or not (as this info is in the MBR, which has NOTHING to do with the filesystem(s) used).

If you just change one word in jcarle's sentence, everything is right however:

FAT DOS was designed to have a single primary partition and a single extended partition.

It is the Operating System design that may (or may not in the case of DOS) allow for several primary partitions.

About the MBR, as hinted before, though the de facto standard allows for 4 partition entries, there are "special" MBR that allow for more than 4:

http://en.wikipedia.org/wiki/Master_boot_record

By convention, there are exactly four primary partition table entries in the MBR Partition Table scheme, although some (rare) systems have been known to extend this to five (PTS-DOS), or even eight, entries.

http://www.win.tue.nl/~aeb/partitions/part...es-2.html#ss2.9

http://mirror.href.com/thestarman/asm/mbr/DOS33MBR.htm

Please note that this has nothing to do with the use of some bootmanagers that allow more than four partitions by using redirections to other sectors on the HD.

jaclaz

[Ponch]

With all due respect, maybe jcarle is the only person knowing what he meant.

I think -with all due respect also- that when common sense applies, other persons know what one means. That's leads to communication, as opposed to monologue.

[eidenk]

If you just change one word in jcarle's sentence, everything is right however:

FAT DOS was designed to have a single primary partition and a single extended partition.

It is the Operating System design that may (or may not in the case of DOS) allow for several primary partitions.

It would appear that this is just true between DOS 3.3 (inclusive) and 5.0 (exclusive) :

MS-DOS 3.3 introduces support for more than one logical drive per hard disk.

Only one PRI DOS partition and one EXT DOS partition is allowed per drive.

MS-DOS versions 5.0 and later support up to eight physical hard disks. MS-DOS versions 5.0 and later support the same partitioning strategy as version 4.x, including Fdisk's inability to create more than one primary MS- DOS partition on a physical disk. However, because some original equipment manufacturer (OEM) partitioning software allows you to create more than one primary MS-DOS partition, MS-DOS versions 5.0 and later have kernel support for up to four primary MS-DOS partitions.

http://support.microsoft.com/kb/69912

Best doc I just found :

After the inquiry DCB has been used to successfully enumerate a drive on the controller, IOS will create the real DCB for the device. The first I/O request for this DCB should be for the MBR (originated from DISKTSD, which reads the partition table and creates logical DCBs for each valid partition it finds).

Windows 95 or Windows 98 Master Boot Record http://support.microsoft.com/kb/192606

and :

From the I-O Supervisor Guide for Windows 9x-Me.

Sorry if I did sound rude or something, I did not mean to.

[jaclaz]

@eidenk

VERY good info!

Essentially we are all saying the same thing, with only some different "shades".

You are very correct in your assumption:

It would appear that this is just true between DOS 3.3 (inclusive) and 5.0 (exclusive)

the slightly different approach I have is a "better safe than sorry" - call it "overcautious" if you like, but reading between the lines of this:

because some original equipment manufacturer (OEM) partitioning software allows you to create more than one primary MS-DOS partition, MS-DOS versions 5.0 and later have kernel support for up to four primary MS-DOS partitions.

.....

This makes it easier to upgrade from previous versions of OEM-modified MS-DOS. Fdisk still creates only one PRI DOS partition on a physical disk.

NOTE: Many OEMs have changed their versions of MS-DOS to support more than one primary MS-DOS partition, larger type 04 partitions, and new partition types.

I understand it as follows:

"Look, since a lot of third parties made modifications to our Operating System DOS, we were forced to implement some of the same modifications, to avoid a prospectively enormous number of calls from customers that when upgrading from one of these modified systems to our new version of DOS, that remains the only GOOD one, risked to loose data, but we DO NOT like this, and we won't allow the abuse of the way DOS is designed to let people choose to have more than one Primary partitions through our tools, in other words, YOU ARE ON YOUR OWN"

Given the above, and the sheer fact that, most probably, a lot of third party tools and utility developers assumed (wrongly) that the only way of partitioning is the "official" FDISK one, I still think Petr recommendation to be valid :

It is not recommended to make more than one primary partition per HDD and Windows 98 SE FDISK does not allow to create them.

as well as my take on the matter:

The point is that a number of Operating Systems (particularly different versions of DOS and Win9x/ME) were developed and tested with the assumption that only one Primary Partitions in the MBR.

Using these operating systems on multiple primary partitioned hard disks can lead, in particular occasions, to data corruption , unlless all partitions but one are "hidden" at boot time, that's the reason why it is "not recommended".

Programmers of tools like the original MS FDISK evidently thought that to be so serious as to include in the tool a mechanism preventing the creation of more than one primary partition.

Several other tools, including Freedos FDISK, do not have such a limitation.

To this you add the possibility, explained in my previous post:

http://www.msfn.org/board/index.php?showto...85729&st=20

Due to the different way letters are assigned, the possibility of creating a "tower of babel" in drive lettering when dual-booting between DOS/WIN98 and NT/2K/XP is concrete if you have multiple primary partitions with filesystems recognized by DOS/WIN98.

As said, the above does not mean impossible, it does not even hints that a problem will or has a probability to happen, only that it can happen, in particular occasions.

Cheers,

jaclaz

[eidenk]

@jaclaz (took me a little time to think about it)

VERY good info!

Glad you like it. I have been myself very happy when I found that.

Essentially we are all saying the same thing, with only some different "shades".

It's all nonsense IMO.

I understand it as follows:

"Look, since a lot of third parties made modifications to our Operating System DOS, we were forced to implement some of the same modifications, to avoid a prospectively enormous number of calls from customers that when upgrading from one of these modified systems to our new version of DOS, that remains the only GOOD one, risked to loose data, but we DO NOT like this, and we won't allow the abuse of the way DOS is designed to let people choose to have more than one Primary partitions through our tools, in other words, YOU ARE ON YOUR OWN"

MS themselves recommend using other tools than fdisk, ie, tools that allow to create several primary partitions on a disk which is the industry standard supported by MS OSes since DOS 5.0. So what of the above argument ?

http://support.microsoft.com/kb/280737

The point is that a number of Operating Systems (particularly different versions of DOS and Win9x/ME) were developed and tested with the assumption that only one Primary Partitions in the MBR.

No they were not, otherwise they would not recommend the above without a warning not to create several primaries.

Using these operating systems on multiple primary partitioned hard disks can lead, in particular occasions, to data corruption , unlless all partitions but one are "hidden" at boot time, that's the reason why it is "not recommended".

Can you specify by an example in which circumstances data corruption may arise and why ?

As far as I can understand, a single boot system with a 9x system on it has a very primitive bootloader which is nothing else than some code in the MBR (of the drive the BIOS boots on) which parses the partition table (also in the MBR) for the active partition and then jumps to the said active partition boot sector which then takes over and loads IO.SYS.

The only problem that I see could arise with several primaries are :

Several partitions are flagged as active, possibly preventing the MBR code to jump to the proper partition or eventually preventing it to jump at all. This can be fixed easily with fdisk or any similar tool.

Windows has been installed on a partition that is not the first of the drive and a new physical disk is subsequently installed. Here, as the 9x serie seems to number logical drives by listing first the first partition of each phyical disk and then only the other partitions (primaries or logicals on extended), problems may arise after IO.SYS has loaded the registry and Windows initialization files which will point to invalid paths as the drive letter on which the OS is installed is likely to have shifted (if no precautions have been taken ?), eventually preventing a full boot of the OS. Here, removing the added drive will immediately solve the problem.

In both cases no data corruption is to be feared.

If the 9x OS is installed on the first primary of the drive and there is only one partition marked as active, no problem at all with ever happen with several primaries.

Due to the different way letters are assigned, the possibility of creating a "tower of babel" in drive lettering when dual-booting between DOS/WIN98 and NT/2K/XP is concrete if you have multiple primary partitions with filesystems recognized by DOS/WIN98.

Could you please elaborate on this "tower of babel" thing and how it could negatively affect things in a different way than the above second scenario in a dual boot setup ?

And correct me where I am wrong cause I am really no expert in that field.

[jaclaz]

Just for the sake of a little polemics, from the link you gave (which is aimed to solve another problem that some version of FDISK have, and where the issue about multiple primary partitions is not at all considered) :

When you use the Fdisk utility to partition a drive that is larger than 512 GB, you might not receive any error messages that state that the drive was not partitioned correctly; however, the drive might not be partitioned correctly. For this reason, use alternative programs when you partition drives that are larger than 512 GB.

The third-party products that are discussed in this article are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.

(bolding is mine)

Not very different from my simplified "YOU ARE ON YOUR OWN".

Moreover, from a pure lexical standpoint, if I tell you that to drive a nail into a wooden plank you can use a Third Party tool called "hammer", it does not mean that I suggest the use of the tool "hammer" to hit your fingers, although the suggested tool is perfectly capable of doing that.

The problem, besides the cases you described, could happen if any app is used that writes to disk using "hardcoded" paths, like D:\, E:\ , etc. if a shift or however a change happened in letter assignments, I am thinking about scheduled jobs like backups or "saving settings", but it could be any similar job, set with a certain existing "drive mapping" that could overwrite something when run once a different "drive mapping" has become effective.

Moreover there is "user" error possibility, I mean, if the nth partition is given "E:" if booted from DOS/9.x and "F:" when booted from NT/2X/XP, there is a probability that the user will once delete something from "E:" thinking he is deleting it from "F:"....

Of course this can be easily worked around by using on the DOS/9.x "side" Letter Assigner and from the NT/2k/XP one manual drive letter assignment to have same lettering in both boot scenarios.

jaclaz