Windows 1.0 Premiere Edition

Microsoft Windows Premiere Edition is a pre-release of Microsoft Windows 1.0. It was sent to key players in computer industry by Microsoft to prove that their product isn't vapourware. Before releasing the official version, 1.01, the memory management code had to be completely rewritten, which should be the key difference between Premiere and 1.01. The build, that was leaked in 2008 and still remains avaliable on several places, is a fake. In March 2014, a BetaArchive user trueyanksfan claimed to have the real floppies, and also posted a photo of them. There are floppy images available on WinWorld, but they may be fake.

Microsoft FTP
A photo of a PC running this build stays on Microsoft's FTP to this day. However, there are doubts about its legitimacy, because the picture is too clear, bright and flat to be a real photo.

Photo from Microsoft FTP

Info from Tandy Trower
In his The Secret Origin of Windows article, Tandy Trower described what Premiere edition was.

But by the early summer of 1985, we were still not close to being done, so Steve [Ballmer] declared we should release a preliminary release that I dubbed the Premiere Edition, which we provided to key application vendors, analysts, and members of the press for feedback and in partial fulfillment of Ballmer’s promise to ship the product that summer.

Because Windows release was postponed several times, some people began to called it a vapourware, a piece of software that is promised all the time but never actually released. This lead Microsoft to make the decision of releasing a preliminary release before it's finished, which they called Premiere edition.

In the same article, he also mentions that:

Then just at the point I was starting to feel more optimistic about wrapping things up the architect of the memory management code told me he found a critical defect in its design and would need to re-write it, basically rendering all testing to date useless.

This means that large portion of the kernel managing memory had to be rewritten, which should be the main difference between Premiere Edition and 1.01.

Also, he mentions another interesting thing:

By November, we had finished testing and come up with a solid release. [...] That release, being after the earlier “Premiere” release, was known as version 1.01.

That implies that there was not any clean 1.00, making 1.01 the first truly public release (Premiere Edition was only sent to key players in computer industry as mentioned before).

Leaked build
The version that was avaliable on BA FTP and that is still avaliable on several other places like WinWorld has been confirmed to be fake. It's because:
 * Microsoft developers stated that the entire memory management was rewritten between Premiere Edition and Windows 1.01, yet the Premiere Edition kernel is codewise identical to 1.01. Even the smallest code change would indicate that this version was different, but nothing is changed between this PE and 1.01 despite developers claims.
 * The original version provided to BA had WRITE.DAT (a file meant for Write) included, but the leaker stated it was a "mistake" and that Write was there only as an experiment. Write is not referenced in the PE setup either. It was later removed in a re-upload, but the fact that it was tampered with from the start raises questions.
 * The leak originated from betaguy224, who has a questionable past of providing fake material.

Trueyanksfan's floppies
On 2014-03-16, a BetaArchive user truyenskfan claimed he has the original floppy disks. Later on, he also posted a photograph depicting 4 5¼" installation disks with "Premiere Edition" clearly written on them.

A few months later, on 2014-09-12, he posted an update, revealing disks 1-3 were overwritten and only disk 4 survived. He also posted a screenshot, claiming that the dates of the files are near end of October 1985.

InfoWorld article
In the Issue 26 Volume 7 of the InfoWorld magazine from 1985-07-01, an article called "Microsoft Ships Windows" was presented. This article describes what seems to be the same thing as Tandy Trower, from the release date to some details (like being given out to "software developers" and "independent software vendors"). However, it doesn't mention the name "Premiere" anywhere, and it's entirely possible that the screenshot is completely unrelated and comes from an older Windows 1.0 Beta version.

Other sources
Stephen Manes and Paul Andrews (1993), Gates, New York: Doubleday, ISBN 0385420757 (a snip talking about premiere)