Windows 95

Windows 95 (codenamed Chicago) is a consumer version of Microsoft Windows released by Microsoft in 1995. It is the first major release in the Windows 9x operating system line, and was designed to be the successor of Windows 3.1. It would be replaced by Windows 98, and Microsoft ended support for Windows 95 on 31 December 2001. It improved upon 16-bit Windows by introducing a hybrid 16/32-bit kernel and eliminating the need for an existing installation of MS-DOS, making it a standalone operating system (running alongside MS-DOS). Microsoft focused on improving the usability of Windows with technologies such as Plug-and-Play, long file names (VFAT), the Start Menu, an updated Desktop, Internet Explorer, Mail, built-in networking, and virtual device drivers. Many of the paradigms introduced with Windows 95 remain in use today.

It was a revolutionary update for Windows, and also the first concerted effort by Microsoft to listen to consumers. Although it was still built upon the solid, if outdated, foundations of MS-DOS, the average user never saw the MS-DOS prompt unless they wanted to. Windows NT was too intensive for most computers of the time, and it was not until after the release of Windows 95 that Win32 applications were widely used and supported.

This is the last version of Windows to be available on 5.25-inch floppy disks, specifically the original release. At this point, Microsoft no longer offered the floppy release of Windows for OEMs, as the CD release became the more widespread one.

Development
The development of Windows 95 started in 1992 shortly after the release of Windows 3.1. Pre-release Windows for Workgroups 3.1 builds were forked into the Cougar project, which attempted to build a 32-bit protected mode kernel to be used in the next Windows-on-DOS release (at the time often called Windows 4.0, Windows 93, or Windows 94). The Cougar project was later merged with Jaguar (known as MS-DOS 7.0, also slated for a separate release) into Chicago, which became Windows 95. The Chicago project additionally took a few components from the Cairo project (meant for Windows NT), including the Cairo user interface, and integrated it into the Chicago shell. Internal Microsoft documents from 1992 occasionally refer to the Chicago project as Windows NT Lite.

The first two builds known to exist are the Usability Testing Builds from December 1992 or January 1993, seen in a Microsoft video. The earliest available build is 58s, known as PDK/M4 from August 1993, followed by builds 73f and 73g (PDK2/M5 from November and December 1993), build 81 (January 1994), builds 89e and 90c (March 1994), build 99 (May 1994), builds 116 and 122 (June 1994), builds 180 and 189 (September 1994, build 189 is the first build to introduce the Windows 95 name), beta 2 builds 216 and 224 (October 1994), beta 3 builds (November 1994 to March 1995), and release candidate builds (mid-1995). The final build of Windows 95, build 950 r-6, would be released to manufacturing on 14 July 1995, and would later be available to the general public on 24 August 1995.

In early 1996, Microsoft released the first OEM Service Release of Windows 95, which was also released to the public as a Service Pack for the RTM build. This is the first version of Windows to include Internet Explorer in its version 2 form, although some OEMs already shipped Internet Explorer 1 with the RTM build. It also introduces infrared support and fixes for bugs which affected the RTM build.

In mid-1996, Microsoft released the second OEM Service Release of Windows 95 (codenamed Detroit), which includes various new features such as FAT32 support, Internet Explorer 3, a newer version of MSN, as well as features that were previously exclusive for Microsoft Plus! 95 such as DriveSpace 3 or Scheduled Tasks (formerly System Agent). An update to it, known as the OEM Service Release 2.1, was released in August 1996, which not only updates Internet Explorer to version 3.02, but it also includes USB support in form of an update package. It is not pre-installed by default, since USB support was still in an early state. It eventually caused Windows to crash more frequently. Another update, known as the OEM Service Release 2.5, was released in November 1997 and updated Internet Explorer to version 4.0, along with it the Active Desktop enhancements, although on incompatible devices, it still ships with IE 2. This is the last update for Windows 95 before being replaced with Windows 98.

Product Team credits Easter egg
There is a hidden Easter egg, which can be accessed by creating a new folder and renaming it to each of the following names in order:
 * and now, the moment you've all been waiting for
 * we proudly present for your viewing pleasure
 * The Microsoft Windows 95 Product Team!

Opening the folder after the last rename opens an Explorer window, although the file list area is replaced with an animation of names of people involved in the development of Windows 95 on a blue cloudy background with  playing in the background. This MIDI file is also subsequently added to the  directory upon launching the Easter egg.

The text is located in the library's resource  and XORed with   as an obfuscation measure. Likewise, the Easter egg folder names are stored in the  section of   as custom hashes of the old folder name concatenated with the new folder name.

This Easter egg is also present in Windows NT 4.0, with references to "95" being replaced with "NT".

Upgrade Check Password
Holding Ctrl and clicking Exit Setup on an Upgrade Check dialog opens a password request screen, containing a random ID Number and a random Key. The valid Password is derived from the Key:. Entering a valid Password passes the upgrade check. This was implemented in  by build 89e, and was most likely used on direction from Microsoft Support Services.