bios/dos to prioritize letter assignment for first drive's partitions.
- The bios does not assign drive letters
- The way DOS drive letter assignment algorithms can't be changed (see
below) so you'd need to figure out a way around them.
You'll notice when reading the below that DOS:
1. Assigns c: to first pri partition on 1st physical drive
2. Assigns d: to first pri partition on 2nd physical drive
The trick is hiding the partition from DOS. A hidden partition will not be
assigned a drive letter. Hiding is in fact nothing else than replacing the
partition type descriptor byte in the partition table with a type that DOS
doesn't know. Convention is simply put to change the Byte describing the
partition 0n -> 1n (where n is a hex value for example 06 (FAT16) become 16.
You could accomplish this using our (free) utility MBRtool which can be run
from the command line and can be integrated into batch files. MBRtool
returns error levels.
=======
Order in Which MS-DOS and Windows Assign Drive Letters
SUMMARY
Microsoft MS-DOS assigns drive letters to the first two physical floppy disk
drives and hard disk drives it finds at boot time in a fixed sequence,
including multiple partitions and logical drives on the hard disks. You
cannot change this sequence.
The drive letters assigned to additional drives installed using DRIVER.SYS
and other installable device drivers is dependent upon the order in which
the drivers are loaded in the CONFIG.SYS file. These drive letter
assignments can be influenced by changing the order of the CONFIG.SYS
statements or loading "dummy" drives to "use up" drive letters.
Drive letter assignments can change when you upgrade from one Microsoft
MS-DOS version to another or from an original equipment manufacturer (OEM)
version of MS-DOS to another version that assigns drive letters differently.
(The order in which drive letters are assigned was modified by OEMs in
earlier versions of MS-DOS.) This article describes how MS-DOS assigns drive
letters; it does not explain how particular OEM MS-DOS versions assign drive
letters.
MORE INFORMATION
The following occurs at startup:
MS-DOS checks all installed disk devices, assigning the drive letter A to
the first physical floppy disk drive that is found.
If a second physical floppy disk drive is present, it is assigned drive
letter B. If it is not present, a logical drive B is created that uses the
first physical floppy disk drive.
Regardless of whether a second floppy disk drive is present, MS-DOS then
assigns the drive letter C to the primary MS-DOS partition on the first
physical hard disk, and then goes on to check for a second hard disk.
If a second physical hard disk is found, and a primary partition exists on
the second physical drive, the primary MS-DOS partition on the second
physical hard drive is assigned the letter D. MS-DOS version 5.0, which
supports up to eight physical drives, will continue to search for more
physical hard disk drives at this point. For example, if a third physical
hard disk is found, and a primary partition exists on the third physical
drive, the primary MS-DOS partition on the third physical hard drive is
assigned the letter E.
MS-DOS returns to the first physical hard disk drive and assigns drive
letters to any additional logical drives (in extended MS-DOS partitions) on
that drive in sequence.
MS-DOS repeats this process for the second physical hard disk drive, if
present. MS-DOS 5.0 will repeat this process for up to eight physical hard
drives, if present. After all logical drives (in extended MS-DOS partitions)
have been assigned drive letters, MS-DOS 5.0 returns to the first physical
drive and assigns drive letters to any other primary MS-DOS partitions that
exist, then searches other physical drives for additional primary MS-DOS
partitions. This support for multiple primary MS-DOS partitions was added to
version 5.0 for backward compatibility with the previous OEM MS-DOS versions
that support multiple primary partitions.
After all logical drives on the hard disk(s) have been assigned drive
letters, drive letters are assigned to drives installed using DRIVER.SYS or
created using RAMDRIVE.SYS in the order in which the drivers are loaded in
the CONFIG.SYS file. Which drive letters are assigned to which devices can
be influenced by changing the order of the device drivers or, if necessary,
by creating "dummy" drive letters with DRIVER.SYS.
The MS-DOS utility SUBST, networks and programs such as the CD-ROM
Extensions which use the MS-DOS network interface can request a specific
drive letter be assigned to a block device.
Example 1
Consider as an example a system with one floppy disk drive and one hard disk
drive, with two MS-DOS partitions (a primary partition and an extended
partition containing a single logical drive) on the hard disk. In this
configuration, MS-DOS will assign the floppy disk drive as drives A and B,
the primary partition on the hard disk drive as drive C, and the logical
drive in the extended partition as drive D.
Example 2
Consider another system with three floppy disk drives, the third drive being
installed using DRIVER.SYS, and two hard disk drives, with a primary and an
extended partition on each hard disk drive. The extended partition on the
first hard disk drive contains two logical drives, and the extended MS-DOS
partition on the second hard disk drive contains one logical drive. A RAM
disk is also created using RAMDRIVE.SYS.
In this configuration, MS-DOS will assign the first two floppy disk drives
as drives A and B, then assign the primary partitions on the first and
second physical hard disk drives as drives C and D, respectively. MS-DOS
will then assign the drive letters E and F to the two logical drives in the
extended partition on the first physical drive, and G to the logical drive
in the extended partition on the second physical drive.
The third floppy disk drive, installed using DRIVER.SYS, and the RAM disk
created using RAMDRIVE.SYS, will be assigned the letters H and I in the
order in which the DEVICE= statements appear in the CONFIG.SYS file.
Partitioning Schemes
Listed below are some sample partitioning schemes for two 40-megabyte (MB)
hard disk drives and their resulting drive letter assignments:
Drive 1:
C: 20 MB primary MS-DOS partition
E: 20 MB logical drive 1 in extended MS-DOS partition
Drive 2:
D: 20 MB primary MS-DOS partition
F: 20 MB logical drive 1 in extended MS-DOS partition
Drive 1:
C: 20 MB primary MS-DOS partition
D: 20 MB logical drive 1 in extended MS-DOS partition
Drive 2:
E: 20 MB logical drive 1 in extended MS-DOS partition
F: 20 MB logical drive 2 in extended MS-DOS partition
Drive 1:
C: 10 MB primary MS-DOS partition
E: 10 MB logical drive 1 in extended MS-DOS partition
F: 10 MB logical drive 2 in extended MS-DOS partition
G: 10 MB logical drive 3 in extended MS-DOS partition
Drive 2:
D: 10 MB primary MS-DOS partition
H: 10 MB logical drive 1 in extended MS-DOS partition
I: 10 MB logical drive 2 in extended MS-DOS partition
J: 10 MB logical drive 3 in extended MS-DOS partition
Regards,
Joep
--
D I Y D a t a R e c o v e r y . N L - Data & Disaster Recovery Tools
http://www.diydatarecovery.nl
http://www.diydatarecovery.com
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DiskPatch - MBR, Partition, boot sector repair and recovery.
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MBRtool - Freeware MBR backup and restore.
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