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SATA/IDE Drive Letter Assignments

By hverne ·
If I have 2 IDE drives, each of which has 2 partitions, so that they are assigned as drives:
C/E, D/F
I have 2 CD Drives, G & H

If I add an Serial ATA disk what letter is assigned to it? How are my existing drive assignments changed?

Yes I know I can change the drive letter in windows but I like to keep my window (WINXP) drive letter assignments the same as my DOS assignments.

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by TheChas In reply to SATA/IDE Drive Letter As ...

XP will assign new drives the next available drive letter.

So, the next new drive will be assigned letter I.

Under DOS, the letter assignments are handled differently.

Primary DOS partitions in order.
Logical drives in order by drive order.
CD Drives.

If you change the drive letters for the CD drives to H and I you can make the new drive become G for both XP and DOS if you partition it with just an Extended partition and NO primary DOS partition.


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by TheChas In reply to

XP gets a bit tricky with making a new drive the boot drive.

Depending on how the system is setup when you boot from the SATA drive will determine the assigned drive letter.

If you have JUST the SATA drive installed, it should become the "C:" drive.
However, if you then connect a bootable volume as the Primary Master drive, it may become C:

By default, any hard drives connected to the Primary or secondary IDE controllers would be assigned as first drives.
Followed by on board hard drive controllers.
Then plug-in drive controller cards.

What sets this is the sequence that the POST in the BIOS enumerates the drive controllers.

Changing the BIOS boot sequence does not change the DOS level drive letter assignments.

As I stated before, and you may understand, Windows XP assigns it's default drive letters in the order the drives are added to the system.

In your concept to make the SATA drive your boot / C: drive, it would need to be the first drive seen by the XP installer to be assigned as C:
Then, when you add hard drives connected to the standard IDE controllers, they will be assigned letters in sequence.

However, DOS will see the drives connected to the standard IDE controller as the first drives. Then, if DOS can even see the SATA controller, the SATA drives will be higher letters.

Or have I just confused you more?


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by TheChas In reply to

A for-instance:

Let us say that you set up a SATA drive as your boot drive and install XP to a single partition on the drive.

After XP is up and running, you add in 2 standard IDE drives connected to the Primary IDE controller.
Both of these drives have a primary DOS partition, and a logical drive in the extended DOS partition.

For XP then:
IDE master = / F:
IDE slave = E: / G:

For DOS:
IDE master = C: / F:
IDE slave = / G:

At least, that is how it "should" work as I understand things.

Keep in mind that "normally" you set up XP on NTFS formated drives and DOS cannot see or access a NTFS volume.
For the purpose of a DOS window under XP, the XP drive letter assignments should hold true.

As another side note:
XP has a built in limit of 32GB for volumes formatted as FAT32.
That is, XP itself will not format any FAT 32 drive to a size larger than 32GB.

You can use the W98 or Me fdisk utility to format larger drives as FAT32 volumes and then install XP. Or use them on an XP system.

However, even the latest version of fdisk for W98 / Me is limited to 137GB total drive capacity.


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by hverne In reply to

Bottom line:
I can't replace one of my IDE drives with an SATA drive and have everything work the same (i.e. have the same drive letters) in DOS and WINXP.

Furthermore I cant take my systsm IDE drive, copy it to an SATA drive and still have it multi boot into either DOS or WINXP (or LINUX).

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by hverne In reply to SATA/IDE Drive Letter As ...

If I have one IDE drive and one SATA :
If the IDE drive is the bootable system drive, will the SATA drive be drive D?

Assuming my BIOS supports booting from the SATA drive, will the SATA drive be C (if I boot from it) and the IDE drive D?

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by softcorp.us In reply to SATA/IDE Drive Letter As ...


Chas has covered this well. Give Chas the points here :-).

Something to add about very large FAT32 drives. Everything Chas said about size limitations on FAT32 is correct. In addition:

1. FAT32 partitions larger than 32GB can be formatted by Symantec Partition Magic on Windows XP.

2. FAT32 partitions larger than 137 GB can be formatted by Symantec Partition Magic on Windows 9X (and XP).

3. Very large FAT32 partitions are not advisable. They will work. But, FAT32 is not as space-efficient as NTFS with very large partitions. There will be a lot of wasted overhead space with such a FAT32 volume. And, whenever an error occurs, it will take a long time to run CHKDSK on a large FAT32 volume. With NTFS, recovery is very quick due to journalling.


-----Steve Jackson

Software Corporation (Softcorp)
Advanced pro bono tools and utilities free for personal use

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by hverne In reply to SATA/IDE Drive Letter As ...

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