Other than Windows 7 and Windows Vista, disk images of Windows 8, Windows 8.1 and Windows 10 have never been available for public download, and most probably will never be. Digital River used to provide ISO files for the previous versions of Microsoft Windows, however, Microsoft is no longer using their servers to distribute Windows since Windows 8 was released. This article describes some alternative download options.
Windows 8 on Digital River
Up until recently, there was a notice on windows7.digitalriver.com that the Digital River Windows Store has closed down. Now even the subdomain isn't available any longer. It seems that Microsoft now wants to distribute Windows exclusively through their own website. We do not expect any future Windows versions to become available on the download domain digitalrivercontent.net or the Digital River Azure storage.
Windows 8 left-over lot on Amazon
If you prefer to hold a physical disk of Windows 8 in your hands, you can get one from the leftover stock of the initial upgrade offer at Amazon. This version can be upgraded to Windows 8.1 free of charge. In fact, this option is much cheaper than purchasing a full version. Microsoft stopped distribution of the initial offer on 31 January 2013, but Amazon still seems to have some stock remaining:
Windows 8.x Test Drive
If you don't want to spend any money now, but still have a look at the final release of Windows 8.1, you can download a 90 days evaluation version of Windows 8.1 Enterprise. The previous release Windows 8.0 is also available for evaluation.
After the 90 days are over, these versions can't be converted to a full product by entering a purchased product key.
Install now, Activate later
In previous versions, it was possible to install Windows without key, run it as trial for up to 120 days, and enter a product key later. This option on first sight seems to have been removed in Windows 8.
However, it's still possible to pre-install Windows 8 or Windows 8.1 with a generic key. These keys can only install Windows. It's not possible to activate it unless you enter an original key purchased from Microsoft. Here they come...
XKY4K-2NRWR-8F6P2-448RF-CRYQH (Windows 8 Professional)
RR3BN-3YY9P-9D7FC-7J4YF-QGJXW (Windows 8 Professional with Media Center)
FB4WR-32NVD-4RW79-XQFWH-CYQG3 (Windows 8 [Home])
XHQ8N-C3MCJ-RQXB6-WCHYG-C9WKB (Windows 8.1 Professional)
GBFNG-2X3TC-8R27F-RMKYB-JK7QT (Windows 8.1 Professional with Media Center)
334NH-RXG76-64THK-C7CKG-D3VPT (Windows 8.1 [Home])
If you can get hold of the installation disk, you can use these keys to install now, and purchase an activation key after 30 days. Rearming the trial period is no longer possible as of Windows 8, therefore, after the initial 30 days' trial period the installation becomes useless until you enter a valid product key.
The Windows 8 and Windows 8.1 Setup Tools
If you have a valid Windows 8 or 8.1 product key (it used to work for all keys, but now there seem to be some restrictions), you can produce an iso file using the Windows 8 Setup Tool. Download and execute the file Windows8-Setup.exe from Microsoft, enter your product key, and have the tool download the Windows 8 or 8.1 setup files. The tool will then be able to compile an iso file or bootable USB stick from the download. This procedure however has some restrictions, as it will determine the language and bit edition of the download from the system on which it is executed, and doesn't allow to change these parameters.
Should you require a different language or bit edition of Windows 8.x, you can still get access to the respective iso file if you install a matching version of Windows 7 first, for example into a virtual machine or on a spare computer. Here's a large selection of Windows 7 installation media in both 32 and 64 bit. Then just run the Windows 8.x setup tool on the Windows 7 installation that matches the required edition.
Windows 10 Technical Preview
Windows 10 is currently available as a Technical Preview. Please check back on this site on any updates on download options once the release date for Windows 10 comes closer.
Windows Free for Students
Those of us who are still at college, and whose institution provides access to Microsoft DreamSpark Premium, are among the especially privileged. If that's the case for you, consider yourself lucky! You'll get Windows 8.1 free!