Why windows can not be installed in an external USB drive?

> Because booting from such drives is not supported. You can use an external
> SATA enclosure with a SATA drive in it if you use an external SATA or eSATA
> port to connect it to your motherboard. There are also ways to use scsi
> drives externally as boot devices.
>
> It has something to do with how drives must be connected to the PCI bus in
> order to be detected in time for booting the system at startup. USB devices
> are on a USB bus and not the PCI bus. The BIOS in many systems now have a
> setting for usb boot but the usb enclosures do not have firmware to do it
> and the usb ports on motherboards do not support it because the USB bus does
> not support it. The operative statement from MS is: (from
> http://www.microsoft.com/whdc/device.../usb-boot.mspx)
>
> "Current versions of Windows should not be installed to USB hard disk drives
> because Windows does not support USB hard disk drives as the primary boot
> device."
>
> The article then continues with proposals to the standards committee:
>
> "This paper introduces the expected industry participation related to the
> following:"
>
> You can read the details from the article linked above.
>
> The international standards committee on this subject is still working
> towards the standards needed for everyone to be on the same page so that usb
> booting can be implemented. Microsoft has said that they will not have usb
> booting in Vista but are looking at it for future releases of Windows.
>
> "Alvaro" <alvaro@gmail.com> wrote in message
> news:CC0F6DC3-94D5-4076-A124-E799E29AAD7C@microsoft.com...

> > Please, could anybody tell me what is the reason why Windows XP and Vista
> > cannot be installed in an external USB 2.0 Hrad drive?
> >
> > Thank you very much.
> > --
> > Alvaro

>
>
>

> The only problem i have with this statement is that certain flavours of
> linux
> can do this. I also have a bootable usb2.0 drive that gets me to dos
> (with
> full access to the usb drive - comes up as c:\) The are plenty of sites
> with
> information on this... surely MSFT could incorporate it if they wanted
> to...
> although you would have all sorts of activation trouble if you booted it
> in a
> different PC each time... maybe that is what they are afraid of???
>
> "Colin Barnhorst" wrote:
>

>> Because booting from such drives is not supported. You can use an
>> external
>> SATA enclosure with a SATA drive in it if you use an external SATA or
>> eSATA
>> port to connect it to your motherboard. There are also ways to use scsi
>> drives externally as boot devices.
>>
>> It has something to do with how drives must be connected to the PCI bus
>> in
>> order to be detected in time for booting the system at startup. USB
>> devices
>> are on a USB bus and not the PCI bus. The BIOS in many systems now have
>> a
>> setting for usb boot but the usb enclosures do not have firmware to do it
>> and the usb ports on motherboards do not support it because the USB bus
>> does
>> not support it. The operative statement from MS is: (from
>> http://www.microsoft.com/whdc/device.../usb-boot.mspx)
>>
>> "Current versions of Windows should not be installed to USB hard disk
>> drives
>> because Windows does not support USB hard disk drives as the primary boot
>> device."
>>
>> The article then continues with proposals to the standards committee:
>>
>> "This paper introduces the expected industry participation related to
>> the
>> following:"
>>
>> You can read the details from the article linked above.
>>
>> The international standards committee on this subject is still working
>> towards the standards needed for everyone to be on the same page so that
>> usb
>> booting can be implemented. Microsoft has said that they will not have
>> usb
>> booting in Vista but are looking at it for future releases of Windows.
>>
>> "Alvaro" <alvaro@gmail.com> wrote in message
>> news:CC0F6DC3-94D5-4076-A124-E799E29AAD7C@microsoft.com...

>> > Please, could anybody tell me what is the reason why Windows XP and
>> > Vista
>> > cannot be installed in an external USB 2.0 Hrad drive?
>> >
>> > Thank you very much.
>> > --
>> > Alvaro

>>
>>
>>