Windows 1.0

Windows 1.0 (codenamed "Interface Manager") is the first version of Microsoft Windows, announced on 10 November 1983. The retail release was originally going to be held in April 1984, but was later pushed back to June 1985, and was then eventually released to retail stores on 20 November 1985.

According to Microsoft, Windows 1.0 is a 16-bit "Operating Environment" designed to run on top of MS-DOS and is not a standalone operating system. This version was succeeded by Windows 2.x.

History
In 1981, the Apps division of Microsoft (Microsoft had two primary divisions during this time - "Systems" and "Apps", for systems software and application development respectively) began to develop a common interface library for all of the productivity applications being developed within the division at the time (mostly Word and the Multiplan spreadsheet). This went by several names, notably MUSH (Microsoft User SHell) and Interface Manager, and is an entirely text-mode UI framework signified by the "session control" strip with context-specific commands at the bottom of the screen. There were also brief plans for a "visual shell" using this UI to be shipped using DOS 2.0, but these were scrapped before the final release. Variants of the MUSH/Interface Manager interface would ship in DOS Word 1.0 and Multiplan in 1982 and 1983, after the development of the Windows product had already begun.

At the same time that Interface Manager was being developed, a European standards committee was developing a standard for computer graphics, known as GKS. Microsoft wished to create a software product that would implement this standard on top of MS-DOS in a device-independent manner; Microsoft hired a developer to start this endeavour at the beginning of 1982, with another being transferred from Compiled Basic to assist with shrinking the code down later (mostly by converting it from C to assembly to meet the memory limitations of early IBM PCs) later that year. This project was dubbed GDI (Graphics Device Independence), later renamed to Graphics Device Interface, initially focusing on vector graphics.

It was eventually decided in the middle of 1982 to merge the Interface Manager and GDI teams into one team to develop a GUI-based package with device-independent graphics drawing, which gradually evolved into a (mostly) fully-fledged operating system with its own API and executable format. Initially this was called "Microsoft Window Manager"; a series of mockups and demo applications designed to resemble the final product (Demonstration Version 0.01) was shown off to BYTE Magazine in September 1983 under this name, featuring overlapping windows and showcasing both "cooperative" and "uncooperative" DOS applications that directly modified video memory. The product had been renamed to "Windows" by the time it was announced on 10 November 1983, with an early build demoed at COMDEX '83 two weeks later. By this time, the design of the standard window had changed to a design closer to the final version, with tiled windows (these were not done for copyright reasons and were instead done because of usability studies from Xerox PARC, where some of the original developers of Windows were hired from) and a messagebar at the top of the screen that would eventually be removed later in the product's development cycle (the UI changes being significant enough for BYTE to mention in their article). The original announced release date was April of 1984; this slipped several times (the original April 1984 date had already slipped internally, from the end of 1983) and was most likely never realistic in the first place, with a pre-alpha release strictly for developers not even shipping until the end of May.

These development releases were very unstable and represented a rapidly changing system that was in no way even close to being ready for release - despite Microsoft's repeated promises of imminent release - with critical elements required for a functioning operating system such as a functioning memory management system not present until the fifth development release at the end of October 1984 and the executable format and basic API tenets (such as individual registering of procedures being changed to window classes) completely changing several times as late as January of 1985. The development releases were followed with an Alpha Release (with a very different and completely incompatible API to the previous development release 5) in January 1985, followed up by a beta release in May 1985. After yet another release date of summer 1985 was blown up by a critical defect in the aforementioned memory management code necessitating a rewrite, Microsoft sent out the "Premiere Edition", a glorified beta release, to press and OEMs, and at least one OEM shipped a pre-release version of the product (version 1.xx, in September 1985), possibly out of contractual obligations or mere frustration with Microsoft's apparent inability to complete Windows.

After a sustained crunch period throughout the summer and autumn of 1985 and a series of semi-regular beta and "Retail Beta" releases through the next few months, the operating system was finally completed on 14 November 1985, and sent into mass production the next day. While it was a high-quality product with few bugs by all accounts, the operating system was faulted for high hardware requirements, especially requiring expensive, optional hardware for the time (such as a mouse); despite this it was successful enough for Microsoft to begin developing "Windows 1.5", which would count among its features overlapping windows and, in the more expensive "Windows/386" SKU, the VMM (Virtual Machine Monitor) driver, which provided the ability to utilize the features of the Intel 80386 processor to pre-emptively multitask MS-DOS apps. After around two years of work and four external alpha and beta releases, it would be renamed to Windows 2.0, first with version 2.01 released in September 1987 for OEMs, and 2.03 released three months later for retail consumers.

System requirements
According to Microsoft, the following are the recommended system requirements for Windows 1.0 and its beta releases. This table takes account retail versions; OEM versions will vary depending on the hardware that it was intended to be installed on.

Compatibility
Windows 1.0 does not officially support MS-DOS versions above MS-DOS 3.x due to a bug in the logo code that does not accept MS-DOS versions outside of MS-DOS 2.x and 3.x. All versions of Windows 1.0 will crash on startup on MS-DOS 4.00 and above if  is not run on   to report a MS-DOS version between 2.00 and 3.31.

Easter egg
Windows 1.xx and newer versions include an Easter egg, which shows a scrolling list of people that were involved with the development of Windows alongside a "Congrats!" button. Double-clicking the list box also changes the background of the Easter egg window to tiled smiley faces. Windows 2.0 also contains a similar version of this Easter egg. The sequence for triggering the feature depends on the version:
 * 1.xx: Press Alt.
 * 1.01 and later: Hold Alt and then Esc, release Alt and then Esc, press Esc twice and then press Backspace.

The credits are stored as encrypted data appended to the end of bitmap 1 in, which contains the smiley face used in the Easter egg. The contents of the credits changed on multiple occasions throughout the version's lifetime -- the original variant in Windows 1.xx included 20 names in the so-called "The Secret List". The list was later renamed to "The Windows Team" in Windows 1.01 and expanded to 36 names. Windows 1.04 then almost doubled the list's length, bringing it to 66 names total.