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Happy New year all,

I'm having an interesting challenge to keep me busy over this long
weekend. The basic question is: what, on a dual boot W7 system,
determines how partition letters get reassigned?

I installed W7 Pro x64 on an existing Win XP Pro 32 bit system as dual
boot. But first I cloned my existing drive just as a precaution.

The initial partitions on both 500 GB drives were C (XP boot), D, E
and a newly created F for W7.
Install #1: I installed W7 into the F partition and when done I booted
into W7. As expected it made the F partition the C partition, D and E
remained D and E and the XP partition became G since somehow the DVD
drive slipped in as F.

Install # 2: Two weeks later I wanted to install W7 onto the cloned
drive. I didn't do anything different than I did during Install # 1,
but this time when W7 booted up F became C as expected, but the old XP
partition slipped into the D slot and the old D and E were shifted to
E and F!! The DVD drive became G.

My question now is: why did these 2 identical installs come up with
different partition letter assignments?
And how can I force the assignments to look like my first attempt
since I like keeping my data partitions, D & E the same under XP and
W7? Not that it matters to the system as it works either way, but it's
less confusing to me since I would always know that certain data is on
the same partition no matter which OS I'm logged on to.

It seems that he letter swaps must happen in the boot manager. However
I checked into BCDEDIT and the boot tab in msconfig, but found no way
to affect the letter allocations.

Any ideas and suggestions would be very welcome.
Thanks ...

-=tom=-

It's very hard to determine how Windows will enumerate the drives and
partitions in advance. Fortunately you can easily change the drive letters
after the fact. Run diskmgmt.msc then right click a partition or drive to
change the drive letter. Do not change the letter for the partition that the
currently running version of Windows is installed on. You should also not
change the letter for partitions where you have installed programs for the
currently running version of Windows. If it's just data you should be OK.

--
Kerry Brown
MS-MVP - Windows Desktop Experience: Systems Administration
http://www.vistahelp.ca/phpBB2/


"Tom Orle" <> wrote in message
news...
> Happy New year all,
>
> I'm having an interesting challenge to keep me busy over this long
> weekend. The basic question is: what, on a dual boot W7 system,
> determines how partition letters get reassigned?
>
> I installed W7 Pro x64 on an existing Win XP Pro 32 bit system as dual
> boot. But first I cloned my existing drive just as a precaution.
>
> The initial partitions on both 500 GB drives were C (XP boot), D, E
> and a newly created F for W7.
> Install #1: I installed W7 into the F partition and when done I booted
> into W7. As expected it made the F partition the C partition, D and E
> remained D and E and the XP partition became G since somehow the DVD
> drive slipped in as F.
>
> Install # 2: Two weeks later I wanted to install W7 onto the cloned
> drive. I didn't do anything different than I did during Install # 1,
> but this time when W7 booted up F became C as expected, but the old XP
> partition slipped into the D slot and the old D and E were shifted to
> E and F!! The DVD drive became G.
>
> My question now is: why did these 2 identical installs come up with
> different partition letter assignments?
> And how can I force the assignments to look like my first attempt
> since I like keeping my data partitions, D & E the same under XP and
> W7? Not that it matters to the system as it works either way, but it's
> less confusing to me since I would always know that certain data is on
> the same partition no matter which OS I'm logged on to.
>
> It seems that he letter swaps must happen in the boot manager. However
> I checked into BCDEDIT and the boot tab in msconfig, but found no way
> to affect the letter allocations.
>
> Any ideas and suggestions would be very welcome.
> Thanks ...
>
> -=tom=-
>
>

Hi, Tom.

When we install Win7 by booting from the Win7 DVD, Setup has no idea what
letters have already been assigned, so it follows its own rules for the
initial assignment. First, it assigns the letter C: to whichever partition
we choose to "install" it in. This becomes the Win7 "boot volume". Then it
assigns other letters, starting with D:, usually assigned to the "system
volume", if that is not the same partition as the boot volume. (This rule
changed with Vista; WinXP and prior assigned C: to the system volume, then
the next available letter to its own boot volume, if different.) After
installation, we can use Disk Management to change letters on all volumes
except the boot volume and, if different, the system volume. The Status
column of Disk Management shows us which partition has the Boot status and
the System status; the two "status" labels may or may not be on the same
partition. (For these "backwards" definitions, see KB 314470, Definitions
for system volume and boot volume
http://support.microsoft.com/kb/314470/EN-US/ )

But when we boot into an existing Windows installation, then run Win7 Setup
from that desktop, Setup can see the drive letters already assigned by that
existing OS and it will use the same letters, even for the boot and system
volumes.

So, when we add Win7 to an existing Windows system to create a multi-boot
system, we can either have it "inherit" the existing letters (by running
Setup from the existing desktop) or have it assign "C:" to whichever
partition we install it into (by booting from the DVD).

Note that Windows (any version) is just as happy running from X:\Windows as
from C:\Windows. Most users develop a "drive C: mindset" early in their
computing experience and have trouble adapting to having Windows on any
other partition - but Windows itself has no such hangup. If you want your
drive letters to be consistent as you reboot between different Windows
installations, then boot into the first system, assign the letters you want,
and then run Setup from there to install the second system - and the 3rd and
4th OSes, if you want to use that many. Only ONE can say it's on Drive C:,
but neither Vista nor the others will care if Vista is on Drive V:. And
nobody cares if we skip letters and choose some that are easy to remember; I
like to leave gaps that I can fill in later if I get a new thumb drive or
other device.

Win7 has added a new wrinkle by creating a small (100 MB) partition to use
as the System Volume, but that happens only when Win7 is installed on a
computer without an existing OS. I've read about this, but haven't run into
it yet, since I was already multi-booting before installing Win7, so it
simply updated the startup files on my existing System Partition.

BCDEdit uses drive letters, but it cannot change them. We use Setup to
assign letters initially and Disk Management to reassign them - except for
the system and boot volumes.

RC
--
R. C. White, CPA
San Marcos, TX

Microsoft Windows MVP
Windows Live Mail 2009 (14.0.8089.0726) in Win7 Ultimate x64


"Tom Orle" <> wrote in message
news...
> Happy New year all,
>
> I'm having an interesting challenge to keep me busy over this long
> weekend. The basic question is: what, on a dual boot W7 system,
> determines how partition letters get reassigned?
>
> I installed W7 Pro x64 on an existing Win XP Pro 32 bit system as dual
> boot. But first I cloned my existing drive just as a precaution.
>
> The initial partitions on both 500 GB drives were C (XP boot), D, E
> and a newly created F for W7.
> Install #1: I installed W7 into the F partition and when done I booted
> into W7. As expected it made the F partition the C partition, D and E
> remained D and E and the XP partition became G since somehow the DVD
> drive slipped in as F.
>
> Install # 2: Two weeks later I wanted to install W7 onto the cloned
> drive. I didn't do anything different than I did during Install # 1,
> but this time when W7 booted up F became C as expected, but the old XP
> partition slipped into the D slot and the old D and E were shifted to
> E and F!! The DVD drive became G.
>
> My question now is: why did these 2 identical installs come up with
> different partition letter assignments?
> And how can I force the assignments to look like my first attempt
> since I like keeping my data partitions, D & E the same under XP and
> W7? Not that it matters to the system as it works either way, but it's
> less confusing to me since I would always know that certain data is on
> the same partition no matter which OS I'm logged on to.
>
> It seems that he letter swaps must happen in the boot manager. However
> I checked into BCDEDIT and the boot tab in msconfig, but found no way
> to affect the letter allocations.
>
> Any ideas and suggestions would be very welcome.
> Thanks ...
>
> -=tom=-

Hi, Tom.

"Drive" letters are like shifting sands. Especially when dual-booting.
Please don't rely on them. Windows pays very little attention to them.

When dual-booting, OS #1 cannot read OS #2's Registry, so it has no idea
what letters OS #2 might have assigned. So what is Drive X: in WinXP might
be Drive H: in Win7 - or vice versa. To make the drive letters consistent
between the two OSes, you need to run Disk Management in each OS and assign
the same letters in each of them.

But there is a BIG fly in this ointment: Letters for the System Volume and
Boot Volume are assigned by Setup when each OS is installed and cannot be
changed (by us mere mortals) after installation - except by running Setup
again, which means re-installing.

The terms "system volume" and "boot volume" are VERY important in
understanding drive letter assignments - and the definitions are backward
from most users' expectations. As often said, we BOOT from the SYSTEM
partition and keep the operating SYSTEM files in the BOOT volume. Carefully
read KB 314470, Definitions for system volume and boot volume
http://support.microsoft.com/kb/314470/EN-US/ . Until you get these
definitions firmly in mind, dual-booting is not going to make any sense.

WinXP Setup assigns the letter C: to the System Partition, then assigns
other letters according to its built-in algorithm. In the typical system,
with the first partition on the first HDD holding both the System and Boot
volumes, this means that the whole shebang is in Drive C:. Most users never
get past this basic arrangement and never need to really understand drive
letters.

Vista Setup assigns the letter C: to its own Boot Volume - wherever that may
be - even if it is the 3rd partition on the second HDD. Whichever partition
you choose to install Vista in will become Drive C:. That means that,
unless you install it into the System Partition, the System Partition will
have to be assigned a different letter: Drive D:.



"Tom Orle" <> wrote in message
news...
> Happy New year all,
>
> I'm having an interesting challenge to keep me busy over this long
> weekend. The basic question is: what, on a dual boot W7 system,
> determines how partition letters get reassigned?
>
> I installed W7 Pro x64 on an existing Win XP Pro 32 bit system as dual
> boot. But first I cloned my existing drive just as a precaution.
>
> The initial partitions on both 500 GB drives were C (XP boot), D, E
> and a newly created F for W7.
> Install #1: I installed W7 into the F partition and when done I booted
> into W7. As expected it made the F partition the C partition, D and E
> remained D and E and the XP partition became G since somehow the DVD
> drive slipped in as F.
>
> Install # 2: Two weeks later I wanted to install W7 onto the cloned
> drive. I didn't do anything different than I did during Install # 1,
> but this time when W7 booted up F became C as expected, but the old XP
> partition slipped into the D slot and the old D and E were shifted to
> E and F!! The DVD drive became G.
>
> My question now is: why did these 2 identical installs come up with
> different partition letter assignments?
> And how can I force the assignments to look like my first attempt
> since I like keeping my data partitions, D & E the same under XP and
> W7? Not that it matters to the system as it works either way, but it's
> less confusing to me since I would always know that certain data is on
> the same partition no matter which OS I'm logged on to.
>
> It seems that he letter swaps must happen in the boot manager. However
> I checked into BCDEDIT and the boot tab in msconfig, but found no way
> to affect the letter allocations.
>
> Any ideas and suggestions would be very welcome.
> Thanks ...
>
> -=tom=-
>
>

Oops!

Sorry for the double post. This second one was an earlier draft that I
meant to delete, not to send. Please ignore it. :>(

RC
--
R. C. White, CPA
San Marcos, TX

Microsoft Windows MVP
Windows Live Mail 2009 (14.0.8089.0726) in Win7 Ultimate x64

"R. C. White" <> wrote in message
news:uE$...
> Hi, Tom.
>
> "Drive" letters are like shifting sands. Especially when dual-booting.
> Please don't rely on them. Windows pays very little attention to them.
>
<SNIP>

"R. C. White" <> wrote:


>"Drive" letters are like shifting sands. Especially when dual-booting.
>Please don't rely on them. Windows pays very little attention to them.
>
>When dual-booting, OS #1 cannot read OS #2's Registry, so it has no idea
>what letters OS #2 might have assigned. ...

I'm aware of the latter. That's why I installed a piece of software,
like Open Office, twice - once in XP and once in W7 just to make the
respective registry aware of the softwares location. despite having
only one copy of Oo on drive D.

So when drive D got shifted to E I ran into problems. My choice was
to either edit the W7 registry and change all drive references to Oo
from D to E or change the drive letters .
But I lucked out - since both drives were identical copies of each
other and I'm a proud owner of Acronis' backup software and was smart
enough to make a backup copy after the first sucessful install, I
copied/restored just the MBR onto the drive with the shifted letters
and everything fell in place.
This makes me assume that, when booting into W7 on a dual boot
system, it's the boot manager that does the assignments of drive
letters. If I look at bcdedit, it shown W7 on drive F and /ntldr on C,
but after boot W7 is C and the C boot drive containing XP became G!

But thanks to all for your educational insights - I learned a lot.

Happy New Year!!

-=tom=-

Tom Orle wrote:
> Happy New year all,
>
> I'm having an interesting challenge to keep me busy over this long
> weekend. The basic question is: what, on a dual boot W7 system,
> determines how partition letters get reassigned?
>
> I installed W7 Pro x64 on an existing Win XP Pro 32 bit system as dual
> boot. But first I cloned my existing drive just as a precaution.
>
> The initial partitions on both 500 GB drives were C (XP boot), D, E
> and a newly created F for W7.
> Install #1: I installed W7 into the F partition and when done I booted
> into W7. As expected it made the F partition the C partition, D and E
> remained D and E and the XP partition became G since somehow the DVD
> drive slipped in as F.
>
> Install # 2: Two weeks later I wanted to install W7 onto the cloned
> drive. I didn't do anything different than I did during Install # 1,
> but this time when W7 booted up F became C as expected, but the old XP
> partition slipped into the D slot and the old D and E were shifted to
> E and F!! The DVD drive became G.
>
> My question now is: why did these 2 identical installs come up with
> different partition letter assignments?
> And how can I force the assignments to look like my first attempt
> since I like keeping my data partitions, D & E the same under XP and
> W7? Not that it matters to the system as it works either way, but it's
> less confusing to me since I would always know that certain data is on
> the same partition no matter which OS I'm logged on to.
>
> It seems that he letter swaps must happen in the boot manager. However
> I checked into BCDEDIT and the boot tab in msconfig, but found no way
> to affect the letter allocations.
>
> Any ideas and suggestions would be very welcome.
> Thanks ...
>
> -=tom=-
>
>
...