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I am wondering how this works. I'll tell you the story of my computers:

I have one laptop and one desktop. One laptop was running Windows 7 Home Premium (32 bit) and my desktop is running Windows 7 Ultimate 64 bit. Now, I have already upgraded my laptop to Windows 8 Pro and it installed a 32 bit version! I suppose because the installer detected that the previous version was 32 bit. I installed Windows by downloading the ISO and burning it on a DVD.

Now, I want to upgrade my desktop as well! I have already bought the key for Windows 8 (via PayPal using the Upgrade Assistent) but I do not want to waste another DVD if it has the same contents. So, can I use the DVD I used to install Windows in my laptop for my desktop, even though my desktop has a 64 bit OS (and I want it to install a 64 bit Windows 8 as well)?

In other words: the ISO that I downloaded, does it contain the 32 bit and the 64 bit installer? Or does the Upgrade Assistent download the correct (i.e. 32 bit or 64 bit) installer?

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It's dependent on what you already have installed. – KronoS Nov 1 '12 at 18:14
@Karan Nope, the Upgrade DVD in a box that's sold in stores contains two DVDs. There's never both 32 bit and 64 bit OS on the same CD/DVD. – Alexey Ivanov Nov 1 '12 at 18:38
@AlexeyIvanov: Whoops, yes, that's true. I somehow got confused between Core/Pro being in the same ISO. – Karan Nov 1 '12 at 18:52
up vote 4 down vote accepted

Edit: No, the ISO contains either 32 or 64 bit version. Upgrade assistant downloads the correct version – 32 or 64 bit – depending on the hardware.

If you downloaded 32 bit version want 64 bit version, you have to download once again.
The ISO for 64 bit is slightly larger.

If you had 64 bit OS, then you want upgrade to 64 bit Windows 8.

The DVD with 32 bit version of Windows 8 contains only 32 bit version.
By installing 32 bit you limit yourself to using no more than 3.xx GB of RAM. If you have more RAM, you have to download 64 bit installer.

Otherwise you can use the DVD to upgrade as many systems as you want provided you have the key for each of them.

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It's actually up to 4.0gb on 32bit. It's ((2^32) / 1024) / 1024 (because you want MB's which is 4096MB == 4GB – nerdwaller Nov 1 '12 at 18:23
You don't seem to understand the question entirely. I added a last paragraph. – Bram Vanroy Nov 1 '12 at 18:24
@nerdwaller Yes it is. However, some of that 4GB address space is reserved for hardware. Depending on the hardware, the OS will be limited to using 3.2–3.8GB of RAM (from my experience). It depends. But never 4GB sharp. – Alexey Ivanov Nov 1 '12 at 18:26
@BramVanroy I understood it. I might not have conveyed it clearly. I've edited my answer. – Alexey Ivanov Nov 1 '12 at 18:31
You are correct, my apology. Searching Windows 8 on MS pulled up 7 info too. I found an article talking about the retail replacement. Thanks! – nerdwaller Nov 1 '12 at 18:53

Windows 8 installs the version you are on at the moment. If you are currently running 32 bit, then when you Upgrade you will get the 32 bit version. If you are currently running 64 bit, then you will get the 64 bit version.

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+1 After you complete the Upgrade Assistant, visit Download Windows 8 Enterprise 90-Day Evaluation. It sounds stupid, but download the 64-bit evaluation-only product (expires Aug 2013), and install that just for the short length of time you need to download your ACTUAL new paid-for Windows 8 from [Windows Order Summary]( This way, you are riding a 64-bit OS at the time you initiate the download. Or download it on any friend's 64-bit Windows system and walk the USB stick with your treasure back to your own system to install it. – zero2cx Nov 5 '12 at 4:45
@Jakosaur your answer is what I am hoping for - but how do you know? Can you give a reference to official docs? Either that, or have you discovered this from your own experience of the install? I agree that it does make sense for the Windows 8 Pro upgrade download edition to be selected on the basis of the existing installed OS: i.e. if it is 32bit then Windows 8 Pro 32bit is installed. Usually a conscious decision would have been made to select a specific bit version, e.g. 32 bit version supports older devices that don't have 64bit drivers for example. – therobyouknow Jan 28 '13 at 9:28

My answer is that you will need to burn a second DVD with the 64-bit ISO.

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