What determines hard disk number?

  • Thread starter Thread starter Walter R.
  • Start date Start date
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Walter R.

I installed a new hard drive and used an Acronis Drive Image to clone my old
OS to the new drive. The new drive was recognized as Disk 0. This is a 320
GB SATA drive. I set up 3 partitions, including partition C: Active, for
Windows XP

Then I re-installed my other hard drive, which holds data only, in my
computer. This is an IDE drive.

What baffles me, is that Windows changed the SATA drive to disk 1, while the
old IDE drive was now disk 0.

So, the OS resides on C: of Disk 1, instead of on Disk 0.

The system works great, I am just used to seeing C: reside on Disk 0,
instead of Disk 1.

Can I, or should I, change the respective Disk numbers?
 
Walter said:
I installed a new hard drive and used an Acronis Drive Image to
clone my old OS to the new drive. The new drive was recognized as
Disk 0. This is a 320 GB SATA drive. I set up 3 partitions,
including partition C: Active, for Windows XP

Then I re-installed my other hard drive, which holds data only, in
my computer. This is an IDE drive.

What baffles me, is that Windows changed the SATA drive to disk 1,
while the old IDE drive was now disk 0.

So, the OS resides on C: of Disk 1, instead of on Disk 0.

The system works great, I am just used to seeing C: reside on Disk
0, instead of Disk 1.

Can I, or should I, change the respective Disk numbers?
Click to expand...

No - that is a hardware designation - not software.
 
Thanks.

Does it matter if my c: drive (OS) resides on Disk 0 or Disk 1? Any
disadvantages?

Should I just leave it alone?

What is it in the hardware that determines if a disk is 0 or 1? Just
curious?
 
Walter R. said:
Thanks.

Does it matter if my c: drive (OS) resides on Disk 0 or Disk 1? Any
disadvantages?

Should I just leave it alone?

What is it in the hardware that determines if a disk is 0 or 1? Just
curious?
Click to expand...

If you have an IDE HD and a SATA HD, the IDE will be disk 0 and the
SATA will be disk 1. Add another IDE HD and the IDEs will be
disks 0 & 1 and the SATA disk will be disk 2. This is just how the
disks are ordered in hardware, and has no bearing on the operation
of XP. Drives will boot in the order designated in the BIOS. The
disk the boot.ini file is located on will be disk 0 for XP booting.
 
Thank you, Ian.

--
Walter
www.rationality.net
-
Ian D said:
If you have an IDE HD and a SATA HD, the IDE will be disk 0 and the
SATA will be disk 1. Add another IDE HD and the IDEs will be
disks 0 & 1 and the SATA disk will be disk 2. This is just how the
disks are ordered in hardware, and has no bearing on the operation
of XP. Drives will boot in the order designated in the BIOS. The
disk the boot.ini file is located on will be disk 0 for XP booting.
Click to expand...
 
Walter R. said:
Thank you, Ian.
Click to expand...

You're welcome. Another interesting thing I have found is
that if you have SATA and eSATA connectors with only
a SATA disk connected, it will be disk 0, but if you then
connect an eSATA disk, it will become disk 0, even if you
are still booting to the SATA disk. A disk connected to the
IDE master will always be disk 0, and the rest will re-rank.
 
Just to add to this, on one PC which I use, I installed a PCI Promise card
that provides two extra IDE channels. The PC sees the card as SCSI. As soon
as I connected an IDE hard drive to that card and rebooted, my boot drive
(which is an IDE drive connected to the motherboard) changed from disk 0 to
disk 1 and the drive connected to the Promise card is seen by Disk Manager
as disk 0.

It's still boots OK with the Disk 0 entry in the boot.ini file as the
Promise card I would guess is not detected by Windows until after the
drivers for this card are loaded.

JS
 
The hard disk number designation is determined by the bios. Many PCs have a
bios selection for boot order of hard drives. This can alter the hard disk
number designation if changed.

The "C:" drive designation is the first active partition found for booting
of the order of hard drive number designation. If hard drive zero has no
active, and primary partition, the bios will go to the next numerical
designation to seek a hard drive with an active, primary partition. This
info is held within each hard disk's master boot record. So such seek time
is minimal.

Older PCs, you had to either select the physical hard drive you want to boot
from in the bios by designation order. This was not a submenu in the bios
settings. Before that, you may have had to disable in the bios settings the
hard drive you normally boot from, in order to boot to another. In even
older situations, the hard drive intent from booting had to be on the
primary ide port. And in those cases, if you wanted to boot from an ide
card, you had to disable the primary ide port in the bios settings.
 
I don't think that XP necessarily follows the BIOS enumeration order. At least
across different classes of device. My %boot%/%system% SATA drive is disk0,
until I plug in a PATA HDD, in which case the boot drive becomes disk1, and
the PATA becomes disk0.

However, I think the BIOS is still enumerating the boot SATA as 0.

If I boot to a floppy and run BootitNG the SATAs are enumerated before the PATA.
I'm pretty sure that BING uses int 0x13 to communicate with HDDs.
 
This BIOS defines "HDD order" and "Boot device priority" seperately.

The Boot order/priority is simply
Floppy
DVD
SATA 0

Currently, the HDD order is set as
SATA 0 (boot drive)
SATA 1
PATA 0

The HDD order is as BootitNG enumerates, but different than Windows disk
management, or a diskpart - list disk, which is;

PATA 0
SATA 0 (boot drive)
SATA 1

OTOH, boot.ini reflects the BIOS order. SATA 0 is rdisk(0).
 
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