Microsoft Windows

• 1. A Window Into Computing

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  Microsoft Windows holds a 79% share of the world's desktop operating systems, a dominance built over four decades from a single program called "Interface Manager". Work on that program began in 1981, years before the product reached consumers. When it finally shipped on the 20th of November 1985 as Windows 1.0, it arrived not as a standalone system but as a graphical shell layered on top of MS-DOS. Windows 1.0 did not allow overlapping windows at all; everything was tiled flat across the screen. That constraint alone tells you how far the technology had to travel before it could conquer the desktop.

  The name itself came from an industry term. At the time, software developers called the graphical boxes that represented programs "windows", and the underlying code "windowing software". Microsoft simply borrowed the vocabulary of the trade. What began as a response to growing interest in graphical user interfaces would eventually fork into families serving personal computers, servers, embedded systems, and cloud-based virtual desktops. The questions worth pursuing are how a shell program became the dominant operating system on Earth, what it took to hold that position, and what vulnerabilities accumulated along the way.

• 2. Early Versions and Lawsuits

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  Windows 1.0 shipped with a modest set of bundled components: Calculator, Calendar, Cardfile, Clipboard Viewer, Clock, Control Panel, Notepad, Paint, Reversi, Terminal, and Write. It extended MS-DOS rather than replacing it, and its shell was a program called the MS-DOS Executive. Popularity was limited.

  Windows 2.0 arrived in December 1987 and introduced more sophisticated keyboard shortcuts along with improvements to memory management. The version after that, Windows 2.03, made a consequential change: it switched from tiled windows to overlapping windows. Apple Computer sued Microsoft over that change, alleging copyright infringement. The case was eventually settled in Microsoft's favor in 1993. Windows 2.1 split into two sub-releases, Windows/286 and Windows/386, the latter using the virtual 8086 mode of the Intel 80386 to run multiple DOS programs simultaneously.

  The real commercial turning point came with Windows 3.0 in 1990. Microsoft rewrote critical operations from C into assembly language to improve speed. The version sold 2 million copies in its first six months, making it the first Windows release to achieve broad commercial success. Windows 3.1, made generally available on the 1st of March 1992, added peer-to-peer networking support through a companion release called Windows for Workgroups in October of that year. Support for Windows 3.1 did not end until the 31st of December 2001, nearly a decade after its release.

• 3. The Consumer Nineties

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  Windows 95 landed on the 24th of August 1995 and reshaped how people thought about personal computers. It introduced native 32-bit applications, plug and play hardware detection, preemptive multitasking, and file names of up to 255 characters. The Program Manager that had defined earlier Windows interfaces was replaced by the Start menu, taskbar, and Windows Explorer shell. As Ina Fried of CNET later wrote, "by the time Windows 95 was finally ushered off the market in 2001, it had become a fixture on computer desktops around the world." Microsoft published four OEM Service Releases of Windows 95; the first of those OEM releases was also the first Windows version bundled with Internet Explorer.

  Windows 98 followed on the 25th of June 1998, adding the Windows Driver Model, USB composite device support, ACPI compliance, hibernation, and multi-monitor configurations. A second edition in June 1999 added Internet Explorer 5.0 and Windows Media Player 6.2. Extended support for Windows 98 did not conclude until the 11th of July 2006.

  On the 14th of September 2000, Microsoft shipped Windows Me, the last DOS-based version of Windows. It arrived with Windows Movie Maker, Windows Media Player 7, and a System Restore utility, but it also removed the ability to access a real-mode DOS environment, breaking compatibility with older software. PC World named Windows Me one of the worst operating systems Microsoft had ever released and placed it fourth on a list of the worst tech products of all time.

• 4. The NT Architecture Shift

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  In November 1988, a new team within Microsoft began work on a revamped operating system originally conceived as a successor to OS/2. That team included Dave Cutler and Mark Lucovsky, who had come from Digital Equipment Corporation. The project was called NT OS/2, and it was designed from the start for security, multi-user access, POSIX compatibility, and preemptive multitasking. After Windows 3.0 succeeded in the consumer market, the NT team pivoted the project to use a 32-bit extension of the Windows API called Win32 instead of the OS/2 APIs. IBM objected to the change and continued OS/2 development independently.

  The NT kernel was designed as a modified microkernel, influenced by the Mach microkernel developed by Richard Rashid at Carnegie Mellon University, though it did not meet the criteria of a pure microkernel. Windows NT 3.1, named deliberately to align it with the consumer Windows 3.1, shipped in July 1993. Windows NT 3.5 followed in September 1994, with a focus on performance and Novell NetWare support. Windows NT 4.0 in June 1996 brought the Windows 95 interface to the NT line.

  Windows 2000, released on the 17th of February 2000, dropped the NT name entirely to focus on the Windows brand. Its successor, Windows XP, released to the public on the 25th of October 2001, was the first version to unify the consumer Windows 9x line with the NT architecture. XP shipped in Home, Professional, Media Center, and Tablet PC editions, and its extended support did not end until the 8th of April 2014.

• 5. Security Vulnerabilities and Responses

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  Early Windows versions were designed at a time when malware was rare and networking was limited, so they carried almost no security architecture. The Windows 9x series allowed any user to edit any other user's files because it had no concept of access privileges. It also left the first megabyte of memory accessible to user-level applications; that memory region contained code critical to operating system function, and a faulty program writing into it could crash or freeze the entire system.

  Windows NT addressed those gaps with full memory protection and access privileges. Prior to Windows Vista, however, the default account created during Windows setup was an administrator account with full system access. Most home users never changed that setting, partly because many programs required administrator rights to function. In a 2002 strategy memo titled "Trustworthy computing" sent to every Microsoft employee, Bill Gates declared that security should become Microsoft's highest priority.

  Windows Vista responded with User Account Control, a privilege elevation system that assigns restricted tokens even to administrator accounts and prompts for explicit consent before elevating a process. Windows Defender antivirus, Secure Boot, BitLocker disk encryption, Control Flow Guard, and ransomware protection were added in later versions. In August 2019, security experts identified the BlueKeep vulnerability in the Remote Desktop Protocol, which could allow remote code execution on older unpatched Windows versions; related flaws called DejaBlue affected newer versions including Windows 7. In July 2024, a CrowdStrike update caused 8.5 million Windows PCs to crash, prompting Microsoft to announce plans to limit kernel access and to rewrite parts of Windows in Rust, a memory-safe language.

• 6. Windows Beyond the Desktop

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  Windows CE, officially known as Windows Embedded Compact, carried Windows onto devices with minimal hardware: satellite navigation systems, mobile phones, and other low-power machines. Microsoft licensed it to OEMs who could modify the user interface while relying on the underlying CE kernel. Sega used Windows CE in the Dreamcast console alongside its own proprietary OS. The CE kernel also served as the foundation for Windows Mobile and influenced Windows Phone 7, which drew on components from Windows CE 6.0 R3 and Windows CE 7.0.

  Xbox consoles from the Xbox One onward run a version of Windows that Microsoft has not officially named; observers call it Xbox OS. The Xbox One implementation runs three operating systems simultaneously using Hyper-V virtualization: the core OS, a games OS, and a more general Windows-like environment for applications. The underlying kernel started at NT 6.2 and the latest version runs on an NT 10.0 base. Microsoft updates the Xbox OS every month via Xbox Live.

  In July 2021, Microsoft announced Windows 365, a subscription service delivering virtualized Windows desktops accessible through any web browser on any operating system. The service was designed to serve businesses adopting hybrid work arrangements during the COVID-19 pandemic. Microsoft made Windows 365 available to business and enterprise customers on the 2nd of August 2021. By bypassing Google Play and the Apple App Store, the browser-based delivery model also lets Microsoft reach Apple and Android users without going through competing app distribution channels.

• 7. Version Control and Source Scale

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  Managing the Windows source code has been an engineering challenge of its own. Before Windows 2000, Microsoft used an internal system called Source Library Manager. After Windows 2000 shipped, they switched to a fork of Perforce named Source Depot, which divided the Windows codebase across 65 separate repositories. By 2017, the codebase had grown beyond what Source Depot could handle. Microsoft began integrating Git into Team Foundation Server in 2013, but Windows and Office continued on Source Depot.

  The migration to Git, announced in 2017 and completed by May of that year, involved 3.5 million separate files in a 300-gigabyte repository. By that May, 90 percent of Microsoft's engineering team was using Git, generating around 8,500 commits and 1,760 Windows builds per day. To handle the scale of a Git repository that large, Microsoft developed a project called the Virtual File System for Git, later known as VFSForGit, which was then superseded by a tool called Scalar in 2021. The sheer volume of daily builds in that repository hints at how continuously Windows is still being modified, patched, and rebuilt, decades after that first tiled-window shell appeared in 1985.