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Is installing Windows 7 in-situ (on a machine running Windows already) less clean that installing at boot time?

For example - you can autorun a Windows 7 disk on a machine that is already booted up into Windows (earlier version).

Does this give a clean install (or is there an option to wipe the hard disk before the install begins?)

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up vote 4 down vote accepted

You can only upgrade from Windows Vista to Windows 7, it will not upgrade from XP.

If you insert a Windows 7 disk and run it from Windows in XP, it would require you to restart and also require you install a clean copy of Windows 7 and generally delete/overwrite the XP partition.

If done from Windows Vista, an upgrade check would be performed, and then rebooted and you are given the option to upgrade, or do a clean installation.

Generally a clean installation would be better, but upgrading shouldn't degrade performance much if at all if the system was in good working condition. Still, I always prefer a clean installation.

Update:

I tested inserting a Windows 7 DVD into my computer running Windows 7 Pro, I clicked install, it copied some files and then rebooted where I was given the option to upgrade or do a clean install. Hope that helps you.

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+1 @drew010. Thanks and can you re-install Windows 7 on an existing Windows 7 machine by autorunning the DVD from Windows? – therobyouknow Nov 25 '11 at 8:35
    
Let me know your answer to my further question above and I hope to accept your answer. – therobyouknow Nov 25 '11 at 15:12
    
Updated answer to address your question. Hope that helps. – drew010 Nov 26 '11 at 18:38
    
+1 Accepted @drew010 thankyou. – therobyouknow Dec 4 '11 at 10:05

Yes, you can. The only difference is that, when finished, you will have an archive of your previous installation, in a folder named WINDOWS.OLD. It takes up a substantial amout of disk space but is, in fact, deletable.

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