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From: Percival P. Cassidy on 19 May 2010 11:01
Am I correct in thinking that switching from Compatibility mode to AHCI
requires only the addition of the appropriate driver? No reformatting or
repartitioning of drives?

Perce
From: Paul on 19 May 2010 12:45
Percival P. Cassidy wrote:
> Am I correct in thinking that switching from Compatibility mode to AHCI
> requires only the addition of the appropriate driver? No reformatting or
> repartitioning of drives?
>
> Perce

If your question is, "does AHCI require some aspect of the data on
my disk to change", the answer is no. The data remains the same.

The answer is also OS-specific. Some OSes make the transition easy.
And some make it hard.

Say you're in WinXP. Your disk interface right now is "Compatible".
Try running the AHCI installer. What happens ? Did you see a
complaint about "no hardware detected" or the like ? The thing is,
the installer would run, if the installer detects a match. But the
Southbridge would be in the wrong mode, to match.

If you go to the BIOS, and switch to "AHCI", then you'll discover
the system won't boot. And if the system won't boot, how can you
run that installer ?

And that is Catch-22.

If you look hard enough, you can probably find a way around that,
but it might not be that easy. There is probably a web page out
there, with the necessary recipe to make the change. Good luck.

http://forum.msi.com.tw/index.php?action=printpage;topic=106575.0

To me, the main benefit of AHCI, is for the transition to RAID,
and installing RAID at a later date, and doing a migration from
single disk to multi-disk RAID. Or if you really needed hot-plug
badly enough, I suppose that would be another reason. But how
often do you need to hot-plug and hot-unplug to Intel SATA
ports on the motherboard ? An expensive motherboard, may already
have a separate chip with ESATA interface and its own driver.

As far as I know, Windows 7 can handle discovering either mode of
disk interface. You may see a smoother change from one
mode to the other, with Windows 7.

Paul
From: Percival P. Cassidy on 19 May 2010 14:12
On 05/19/10 12:45 pm, Paul wrote:

>> Am I correct in thinking that switching from Compatibility mode to
>> AHCI requires only the addition of the appropriate driver? No
>> reformatting or repartitioning of drives?

> If your question is, "does AHCI require some aspect of the data on
> my disk to change", the answer is no. The data remains the same.

That was the main concern.

> The answer is also OS-specific. Some OSes make the transition easy.
> And some make it hard.

<details snipped>

Perhaps I should have said more about what I have in mind.

I was planning to move an SATA drive (containing data in two
partitions/volumes, plus an empty volume) from a WinXP machine to a new
machine on which I will install Win7Pro to the empty volume.

Perce
From: Paul on 19 May 2010 14:37
Percival P. Cassidy wrote:
> On 05/19/10 12:45 pm, Paul wrote:
>
>>> Am I correct in thinking that switching from Compatibility mode to
>>> AHCI requires only the addition of the appropriate driver? No
>>> reformatting or repartitioning of drives?
>
>> If your question is, "does AHCI require some aspect of the data on
>> my disk to change", the answer is no. The data remains the same.
>
> That was the main concern.
>
>> The answer is also OS-specific. Some OSes make the transition easy.
>> And some make it hard.
>
> <details snipped>
>
> Perhaps I should have said more about what I have in mind.
>
> I was planning to move an SATA drive (containing data in two
> partitions/volumes, plus an empty volume) from a WinXP machine to a new
> machine on which I will install Win7Pro to the empty volume.
>
> Perce

It boils down to the same thing. Does WinXP have a driver, for
that particular SATA port and operating mode ? If you set the
SATA port on the new build to AHCI, and WinXP doesn't have that
driver, it might not be very happy. And tell you it cannot
boot.

If worse came to worse, you can do a Repair Install of WinXP,
offer a new driver via F6 and a floppy diskette. But a Repair
Install still messes with some stuff, like your version of
Internet Explorer. The repair might go smoother if you have
IE6, rather than one of the newer ones. You'd have to put back
a couple hundred Windows Updates, fix your Windows Media Player,
install SP3 if it isn't already slipstreamed, and so on. But
at least your email database would be untouched, and your other
programs ready to go.

If you dual boot two OSes on the same drive, the boot
flag is set on one partition, and the boot loader
in there can offer a couple lines during boot, with the
OS choices. If you installed Win7 last, then Win7 knows
about the existence of the other Windows OSes, and can place the
appropriate line in its boot manager. And manage the booting
of the two OSes on that disk.

If you have one OS per disk, you manage the booting via your
BIOS popup disk menu. My computer uses F8, and I press F8 and
select between using my WinXP or Win2K disks. I use separate
disks, and there are no entanglements between disks. Each
OS uses its own boot loader, and each boot loader only has
one entry in it (for its own OS). That allows me to unplug drives
and add in others. For example, on my previous motherboard,
I had a 4GB Win98 hard drive (about 10 years old), which I
could plug in, if I felt like running Win98. There has never
been a reason to do that, but that is to illustrate the
advantages of single booting and modular installs.

Single booting is also convenient for testing Linux distros.
If I were to install two or more OSes, including Linux, and
Linux used grub and messed things up, I'd need to know how
to "undo" the install later, to delete the Linux partition
(and grub). Managing multiple OSes on the same disk is
more difficult, especially if you want to delete the
most recently installed OS (the one currently providing
the boot loader to manage choices at startup).

Paul
From: Percival P. Cassidy on 22 May 2010 13:59
On 05/19/10 02:37 pm, Paul wrote:

>>>> Am I correct in thinking that switching from Compatibility mode to
>>>> AHCI requires only the addition of the appropriate driver? No
>>>> reformatting or repartitioning of drives?
>>
>>> If your question is, "does AHCI require some aspect of the data on
>>> my disk to change", the answer is no. The data remains the same.

>> That was the main concern.
>
>>> The answer is also OS-specific. Some OSes make the transition easy.
>>> And some make it hard.
>>
>> <details snipped>
>>
>> Perhaps I should have said more about what I have in mind.
>>
>> I was planning to move an SATA drive (containing data in two
>> partitions/volumes, plus an empty volume) from a WinXP machine to a
>> new machine on which I will install Win7Pro to the empty volume.

> It boils down to the same thing. Does WinXP have a driver, for
> that particular SATA port and operating mode ? If you set the
> SATA port on the new build to AHCI, and WinXP doesn't have that
> driver, it might not be very happy. And tell you it cannot
> boot.

<snip>

But I am not intending to boot from the WinXP volume: what currently is
home to WinXP will be blank when I move the drive to the new machine. I
will boot from the Win7 DVD and let it install to that now-blank volume.

Perce
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