Microsoft Windows 95 (codenamed "Chicago")
Quick introduction
Windows 95 was the biggest change in Windows' history. It got (kinda) got rid of the not-so-user-friendly user interface in Windows 3.1 and introduced the Desktop that we still love today in Windows 8 (haven't you noticed the similarity?)
OK. We're back in 1992 with Windows 3.1 being just released last year, Microsoft found out that IMB has recently published OS/2 2.0 and they have started working on this partially 32-bit Windows version to follow up Windows 3.11 and release in 1993 (naming it Windows 93). At the same time, the MS-DOS team were also working on MS-DOS 7.0 which would later become the kernel of Chicago.
Mixed UIs
50 series
After a relatively short time, we got the 50 series builds. These builds are a mix between Windows 3.1 and Windows 95 and here are some screenshots that I was able to take before the system crashed. In early software, that's a common occurrence.
Desktop UI we still have
100 series
Development continued and then there were the 60 series and 70 series builds which looked very similar and have added more features, made Windows easier to use and overall bug fixes. There was the 80 series builds which kind of started to shape up Windows 95's final look (but I never got it to work so there is no screenshot) and there were the 90 series and finally the 100 series. Windows 95's development ended in the 100 series and this build is known as Build 122. It is also the last (leaked) build to name itself 'Chicago'.
Ending the development
Since this build, Chicago started shaping into Windows 95. It has changed the beta icons to the final icons (even though I like the ones in builds 122 and 189 better), the naming changed and finalized and any so-far noticed system breaking bug has been squashed. This envolved many builds to be built and finally, released with build number 950. And update which eventually brought the build number up to 1216.
The aftermath
Windows 95 is the pioneer in the current desktop layout that we have in Windows and some other operating systems today. This OS has ended support in 2001 with all the updates available and it is interesting still today to use! Following and playing around with the betas were good fun, but still, it's now old.
Want to have a play-around?
Download Windows 95 and pre-release builds here. I know of the fact that Microsoft put a non-disclosure license on it (pre-release builds) and it used to cost (final builds), but it's perfectly legal because it's abandonware! And it also is no longer supported by Microsoft.