Original Link: http://www.anandtech.com/show/3564

One of the nice things to come out of Microsoft’s complete overhaul of the Windows installer for Vista and beyond was that it did away with the idea that different variations of Windows needed different discs. Previously each distribution of XP (Home/Pro/MCE) required its own disc, and then each license type (OEM/Retail/VLK) also required its own disc. This lead to an astounding number of disc types, and complete and utter frustration when for users attempting to install Windows and not having the correct disc to go with the key they had.
With Vista’s image based installer, we saw Microsoft consolidate all of this – one disc could contain every distribution of Windows, allowing a user to always be able to install Windows with any Windows disc, regardless of what their key was. This greatly simplified the installation process, resolving one of the most frustrating things about installing Windows XP.
So imagine our surprise when we’re taking a look at our TechNet copies of Windows 7 and find that there’s a different installation disc for each distribution of Windows. With the version of the Windows installer that comes with Win7, there is a new file at /Sources/ei.cfg that tells the Windows installer what OS it should install. Here’s what the file looks like from the ultimate disc:


When the Windows installer sees this file, it becomes keyed to whatever distribution the file specifies. In this case with an Ultimate disc, we cannot install Home Premium or Professional. We have not yet had a chance to test OEM and retail keys since we don’t have both, however it certainly looks like the installer is going to make a distinction there too.
Perhaps the most interesting bit of this is that the installation process itself hasn’t changed – the Windows installer still supports One Disc to Rule Them All operation, and the Windows image that comes with Ultimate for example has absolutely no problem installing lesser versions. In fact if you remove ei.cfg so that the Windows installer is not told to install a specific version, it will revert to One Disc mode. The distinction between discs is entirely trivial, dictated by a single 51 byte configuration file. You can have a One Disc installer, Microsoft just don’t want it to be the default action for some reason.
Now to be fair, this didn’t entirely catch us off-guard. We first saw this file and its functionality with the Win7 Beta, but until now we did not know if this was something that was specific to the testing versions of Win7, or if it was going to be pushed out in to retail with this limitation. Now we know our answer.
The biggest downer though is that this file is fairly tricky to remove. For copies of Windows packed in ISO files or burnt to discs, this requires remastering the ISO/disc in order to maintain its bootability – it’s not possible to just copy the contents to a new file/disc sans ei.cfg and have a One Disc. Building a proper bootable ISO/disc is still more of a dark art than a science. Users looking to install Windows from a USB flash drive will have an easier time – since installers set up on those types of drives are rewritable it’s easy to remove the offending file. Though this may not be the case with officially distributed flash drives should Microsoft go ahead and distribute Win7 that way, as rumors suggest they will.
In any case this is a significantly disappointing action coming from Microsoft. The One Disc returned the sanity to installing Windows, and made having so many distributions more bearable. Now as far as pressed media is concerned, we’re back to the dark ages of Windows XP (I guess Microsoft really was trying to copy everything about XP?). Geeks would be well advised to burn a copy of Windows 7 with One Disc capabilities as soon as they have it – if the experience is anything like Vista then the benefits will quickly make themselves apparent.

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