Drive Letters

w^rl0rd

O.K. Now I'm really starting to get conflicting information. Let's say I have two IDE channels, two ports on each channel. On my primary IDE channel I have a Hard Drive set to master and a CD ROM set to slave. On my secondary IDE channel I have another Hard Drive set to master and a CDRW set to slave.

Now, according to Microsoft's A+ book, my drive letters will be assigned as follows:

Hard Drive #1 = C:
CD Rom =
Hard Drive #2 = E:
CDRW = F:

Isn't this incorrect?
According to Meyers' All In One, drive letters are assigned Primary partitions first, then extended.

I thought it would be assigned like this:
Hard Drive #1 = C:
Hard Drive #2 =
CD ROM = E:
CDRW = F:

Please, someone clear this up once and for all.

milomorai

You are right and microsoft is wrong. i have just that setup and the letters are assigned to masters first then slaves, primary first then secondary.

w^rl0rd

Thanks milomorai.

According to Meyers, this is the order letters are assigned:

Primary partition on the primary master
Primary partition on the primary slave
Primary partition on the secondary master
Primary partition on the secondary slave
Logical partition on the primary master
Logical partition on the primary slave
Logical partition on the secondary master
Logical partition on the secondary slave

So, even if my second hard drive was a slave on the secondary IDE channel, it should still be assigned D because it is the second primary partition.

You know, it really bothers me that a company can put out incorrect information about something so important. I could have easily bought that book and missed that question on my exam which could have cost me over a hundred dollars. It is very irresponsible and they should be corrected accordingly. I think CompTIA should make publishers submit their publications to them first before allowing them to publish bad material. Thank God for Meyers.

RussS

Shinobi, I would think that Microsoft would know what the defaults on their own system are. I also think that you should recognise that you are able to change things.

The standard setup on 3 of my lab machines is ...

Machine A
IDE 0 Primary - Local Disk - C
IDE 0 Secondary - DVD ROM - D

IDE 1 Primary - CD Writer - E
IDE 1 Secondary - Local Disk - F

IDE 2 Primary - Local Disk - G
IDE 2 Secondary - Local Disk - H

IDE 3 Primary - Local Disk - I
IDE 3 Secondary - Local Disk - J

Machine B
IDE 0 Primary - Local Disk - C
IDE 0 Secondary - CD ROM - D

IDE 1 Primary - CD Writer - E
IDE 1 Secondary - Local Disk (primary partition) - F
IDE 1 Secondary - Local Disk (logical partition) - G

Machine C
IDE 0 Primary - Local Disk (primary partition) - C
IDE 0 Primary - Local Disk (logical partition) - D

IDE 0 Secondary - Local Disk (primary partition) - E
IDE 0 Secondary - Local Disk (logical partition) - F

IDE 1 Primary - Local Disk (primary partition) - G
IDE 1 Primary - Local Disk (logical partition) - H

IDE 1 Primary - CD ROM - I

That definitely follows the Microsoft rule?

RussS

A little more .... or is that a LOT more

Many people feel that drive letters are assigned more or less at random when a computer boots. There is, however, a definite pattern. This pattern should be understood before you add drives (e.g., a Zip or Jaz drive). This page attempts to address that topic.
General Boot Precedence
There is a general order to how drive letters are assigned during the computer's boot process. (Caveat, most of the discussion here applies to DOS/Windows 3.x. Having multiple operating systems on your system can markedly affect the boot drive assignment process. Also, under operating systems like Windows 95 the user has the option of changing drive letters for some installed devices.)
1. Letters "A" and "B" are generally reserved for floppy drives (even if you only have one drive the operating system switches its designation to A: or B: as necessary).
2. Starting with letter "C" all primary partitions found will be assigned letters (this may involve multiple drives and maybe even removable cartridges if they have primary partitions).
3. Once primary partitions are assigned, then logical partitions will be assigned subsequent letters. (Note: This may result in drive letters seemingly skipping back and forth between multiple physical drives, depending on how they are partitioned.)
4. IDE drives will generally be assigned letters before any SCSI drives if both types are on the same system.
5. Drives assigned by drivers in CONFIG.SYS or AUTOEXEC.BAT will be assigned last. They are usually assigned letters in the order they appear in the files, but many drivers have options that allow you to force particular letters to be assigned to a given device. The same is true for drives assigned by operating systems like Windows 95 or Windows 98.
The BIOS is in charge of the boot process. It scans drives and sets up a table. In accord with #4 above, IDE drives are looked at first. In order, the primary master, primary slave, secondary master, and then secondary slave are checked. Then SCSI drives, if any, are checked.
In the event there are several SCSI controllers in the computer, the SCSI BIOS (on the adapter card) takes control. The exact order can vary, but most often the card with the lowest address will get control first. Because control has been given over to the card BIOS, SCSI controllers installed on the motherboard usually don't get control until after the cards have finished (this is not an absolute, but is generally the case).
Multiple drives on any SCSI chain are assigned using their drive ID number with lowest numbers assigned first and higher numbers next in line.
Once this table is set up the first bootable sector is looked for, starting at the top of the table. Control is turned over to that sector to continue the boot process. Under DOS/Windows 3.x drive letters are assigned in the order drives are found with partitions DOS can read in the table (and so generally follow the order listed above, with some exceptions if DOS cannot read the disk).
After the physical devices found by the various BIOSs have been assigned letters DOS continues its startup routines and runs the various startup files (CONFIG.SYS and AUTOEXEC.BAT primarily). Drivers found in these files may assign further drive letters as noted in #5 above.
Caveats and Notes
Adding a drive or changing a SCSI ID can have unintended problems if you are not careful. A common problem is with CD-ROM drives. Often these come in systems with a single hard drive and are therefore assigned as drive by default. Now, a user will add a second hard disk to the system. That hard disk will often be recognized before the CD-ROM in the boot process, thus capturing the drive designation and invalidating all of the program setups that depend on the CD-ROM being drive .
A similar situation would present itself if you have a single drive with a primary partition (drive C:) and a logical partition (drive ). This is often done in order to reduce the sector size and make storage on the drive more efficient. If you now add a second drive with a primary partition, during the boot process that drive will capture the designation and, again, all programs set up to point to drive will be pointing to the wrong place and likely not work.
One way to get around some of these problems is to make certain any drives you add to your system contain only logical partitions (this may require "wasting" a small space at the start of the drive since the DOS FDISK program will want to assign a primary partition; just be certain it is marked "inactive"). Using this technique will most often assure the new disk will show up after the existing fixed drives in the system. (Note: Drives assigned by device drivers will still be assigned higher letters than they had before unless you took steps to optionally assign high drive letters to them when you installed them.)
To add to the confusion, with removable drives, letter assignment may depend upon whether a cartridge is present in the drive when the computer is booted; and, to further confuse things, the assignment letter may change depending on how the cartridge is partitioned (remember from above that primary partitions are assigned before logical partitions). And, of course, the same drive (e.g., a Zip drive) may have a different letter assigned depending upon its connection. A SCSI connection will place the drive before a parallel connection because parallel connections often require a device driver and are therefore loaded later.
Adding an IDE (or EIDE) drive to a system that already has SCSI drives has the potential for causing significant problems. As noted above IDE drives are found first by the BIOS before SCSI drives. So if you add an IDE drive to a system with SCSI drives every drive in the SCSI chain will likely have their drive letters bumped higher. This can cause problems with installed software; and, if you have multiple operating systems booting from those SCSI drive(s) you may have to reinstall them from scratch as some operating systems write specific drive letters into their boot code during install.
As a general rule:
· Create only a single primary partition. Make all other partitions logical, even if it means wasting a small part of a new disk.
· Assign all of the partitions that are found early in the boot process to DOS/Windows using the FAT format. If you need non-FAT partitions for other operating systems place them after the FAT partitions.
· When you have drives assigned by device driver give them high drive letters, leaving space between the fixed drives and device-driver drives. This will allow system expansion (e.g., addition of cartridge drives).
As an example, on a past author-configured system, floppy drives were A: and B:. The fixed drive was C:. A Jaz drive was . Bernoulli drives were E: and F: and the CD-ROM drive was M: (note the space between F: and M: which might be used for other drives on the Bernoulli/Jaz SCSI chain). Network drives were N: through Z:, mapped as needed. This provided flexibility as needed for future expansion.
Windows 95/98
The more advanced operating systems will usually assign drive letters as part of the system boot process instead of via CONFIG.SYS or AUTOEXEC.BAT files. For such drives, if you need to change the drive letter you should be able to open the Control Panel, double click on the System item, and then click on the Device Manager tab. Double click the device you need to change and then click the Settings tab in the Properties dialog box. At the bottom of the Settings page note the area called Reserved Drive Letters. Select the start (and ending) letter to assign to the device and close the dialogs. You will need to restart your computer for the change to become effective.
Note: If you do this be very certain that no software depends upon the old drive letter as it will no longer be assigned to the correct device and you can encounter errors; perhaps serious errors.
In the process above you have the option of assigning both starting and ending drive letters for a device. This is allowed in case you have placed multiple partitions on a given device.

bellboy

shinobi,

you original question was regarding primary partitions and extended partitions. your example only contained primary partitions. i think you were getting primary / secondary partitions mixed up with master / slave on ide channels

w^rl0rd

Actually, it is the ATAPI devices that are throwing me off. Do they count as primary partitions?

RussS

Yes you are totally confused.

As far as the current A+ goes ATAPI drives are CD ROMS and Zip drives.
They have drive letters depending on their status on an IDE connector, but only Hard Drives have partitions.

my main machine is

IDE 0 Primary - Local Disk - C
IDE 0 Secondary - DVDR - D

IDE 1 Primary - Local Disk - E
IDE 1 Secondary - CD Writer - F

IDE 3 Primary - Local Disk - G
IDE 3 Secondary - Local Disk - H

IDE 4 Primary - Local Disk - I
IDE 4 Primary - Local Disk - J


On of my workshop machines

IDE 0 Primary - Local Disk - C
IDE 0 Secondary - CD ROM - D

IDE 1 Primary - CD Writer - E
IDE 1 Secondary - Local Disk (primary partition) - F
IDE 1 Secondary - Local Disk (logical partition) - G

Note that on IDE 1, the CD Writers and Hard Drives are in different locations - this is because they are ATA100/133 and master/slave also depends on which connector they are on the cable (blue/black/grey), but usually when a CDROM is on the same cable as a Hard Drive and the Hard Drive is jumpered as Master then the CDROM will be the slave.

oldgearhead

I always found it made sense to assign X, Y, or Z to the ATAPI drives,
before adding another hard drive or partitioning a hard drive. That way
the physical hard drives are C & D, and the logical drives follow as E, etc..

RussS

I'm just getting lazy in my old age .... lol

I always used to do that too - makes life easier.

jtbez

Yeah, I'm the same, X is always the source CD (acctually a DVD drive) and Y the CDR!!!

Johnta