Windows 95

Windows 95 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of operating systems. The first operating system in the 9x family, it is the successor to Windows 3.1x, and was released to manufacturing on July 14, 1995, and generally to retail on August 24, 1995, almost three months after the release of Windows NT 3.51. Windows 95 merged Microsoft's formerly separate MS-DOS and Microsoft Windows products, and featured significant improvements over its predecessor, most notably in the graphical user interface (GUI) and in its simplified "plug-and-play" features. There were also major changes made to the core components of the operating system, such as moving from a mainly cooperatively multitasked 16-bit architecture to a 32-bit preemptive multitasking architecture, at least when running only 32-bit protected mode applications.

Accompanied by an extensive marketing campaign, Windows 95 introduced numerous functions and features that were featured in later Windows versions, and continue in modern variations to this day, such as the taskbar, notification area, and the "Start" button.

Three years after its introduction, Windows 95 was followed by Windows 98. Microsoft ended mainstream support for Windows 95 on December 31, 2000. Like Windows NT 3.51, Windows 95 received only one year of extended support, ending on December 31, 2001.

Development

The initial design and planning of Windows 95 can be traced back to around March 1992, just around the time before the release of Windows 3.1. At this time, ''Windows for Workgroups 3.11'' and Windows NT 3.1 were still in development. At this point, Microsoft's strategy was to have a next generation, high-end OS based on Windows NT, namely, Cairo, and a low-end, consumer-focused one as an evolution of Windows 3.1. The latter strategy was to develop a 32-bit underlying kernel and filesystem with 32-bit protect mode device drivers in Windows for Workgroups 3.11, to be used as the basis for the next version of Windows, code named "Chicago." Cairo would be Microsoft's next-generation operating system based on Windows NT, featuring a new user interface and an object-based file system, but it was not planned to be shipped before 1994. Cairo would never be shipped, however, although elements from the Cairo project eventually shipped in Windows NT 4.0 in late July 1996, without the object-based file system, which would later evolve into WinFS.

Simultaneously with Windows 3.1's release, IBM started shipping OS/2 2.0. Microsoft realized they required an updated version of Windows that could support 32-bit applications and preemptive multitasking, but could still run on low-end hardware (Windows NT did not). Initially, the "Chicago" team did not know how the product would be packaged. Initial thoughts were there might be two products, MS-DOS 7, which would just be the underlying OS, an evolution of the Windows for Workgroups 3.11 kernel, with a character mode OS on top, and a fully integrated graphical Windows OS. But soon into the project, the idea of MS-DOS 7 was abandoned and the decision was made to develop only an integrated graphical OS Windows "Chicago."

Beta

Before Windows 95's official release, users in the United States and United Kingdom had an opportunity to participate in the Windows 95 Preview Program. For US$19.95/£19.95, users would receive several 3.5-inch floppy disks that would be used to install Windows 95 either as an upgrade from Windows 3.1x or as a fresh installation. Participants were also given a free preview of The Microsoft Network (MSN), the online service that Microsoft launched with Windows 95. During the preview period, Microsoft established various electronic distribution points for promotional and technical documentation on Chicago,Microsoft Windows Chicago Reviewer's Guide
p.282 including a detailed document for media reviewers describing the new system highlights. The preview versions expired in November 1995, after which the user would have to purchase their copy of the final version of Windows 95.

Architecture

Windows 95 was designed to be maximally compatible with existing MS-DOS and 16-bit Windows programs and device drivers while offering a more stable and better performing system. The Windows 95 architecture is an evolution of Windows for Workgroups' 386 enhanced mode.
;Configuration Manager (CONFIGMG):Responsible for implementing Plug and Play functionality; monitoring hardware configuration changes; detecting devices using ''bus enumerators''; and allocating I/O ports, IRQs, DMA channels and memory in a conflict-free fashion.
;Installable File System Manager (Input/Output Subsystem):Coordinates access to supported file systems. Windows 95 initially shipped with support for FAT12, FAT16, the VFAT extension, ISO 9660 (CDFS), Joliet and network redirectors, with later releases supporting FAT32.

Access requests to physical media are sent to ''Input/Output Supervisor'', a component responsible for scheduling the requests. Each physical media has its device driver: access to the disk is performed by a ''port driver'', while access to a SCSI device is handled by a ''miniport'' driver working atop the SCSI layer. Port and Miniport drivers perform I/O operations in 32-bit protected mode, bypassing MS-DOS and BIOS, significantly improving performance. In case there is no native Windows driver for a certain storage device, or if a device is forced to run in compatibility mode, the ''Real Mode Mapper'' can access it through MS-DOS.

32-bit Windows programs are assigned their memory segments, which can be adjusted to any desired size. Memory areas outside the segment cannot be accessed by a program. If a program crashes, nothing else is harmed. Before this, programs used fixed non-exclusive 64 KB segments. While the 64 KB size was a serious handicap in DOS and Windows 3.x, lack of guarantee of exclusiveness was the cause of stability issues because programs sometimes overwrote each other's segments. A crashing Windows 3.x program could knock out surrounding processes.

The Win32 API is implemented by three modules, each consisting of a 16-bit and a 32-bit component:

;Kernel:Provides high-level access to memory and process management, and access to the file system. Consists of KRNL386.EXE, KERNEL32.DLL, and VWIN32.VXD.
;User:Responsible for managing and drawing the various user interface components, such as windows, menus and buttons. Consists of USER.EXE and USER32.DLL.
;Graphics Device Interface (GDI): Responsible for drawing graphics in a device-independent way. Consists of GDI.EXE and GDI32.DLL.

Dependence on MS-DOS

To end-users, MS-DOS appears as an underlying component of Windows 95. For example, it is possible to prevent the loading of the graphical user interface and boot the system into a real-mode MS-DOS environment. This was done by inserting command.com into the autoexec.bat file or changing the BootGUI variable in the MSDOS.SYS file to 0. This sparked debate amongst users and professionals regarding the extent to which Windows 95 is an operating system or merely a graphical shell running on top of MS-DOS.

When the graphical user interface is started, the virtual machine manager takes over the filesystem-related and disk-related functionality. MS-DOS itself is demoted to a compatibility layer for 16-bit device drivers. This contrasts with earlier versions of Windows which rely on MS-DOS to perform file and disk access (Windows for Workgroups 3.11 could also largely bypass MS-DOS when 32-bit file access and 32-bit disk access were enabled). Keeping MS-DOS in memory allows Windows 95 to use DOS device drivers when suitable Windows drivers are unavailable. Windows 95 is capable of using all 16-bit Windows 3.x drivers.

Unlike Windows 3.x, DOS programs running in Windows 95 do not need DOS drivers for the mouse, CD-ROM and sound card; Windows drivers are used instead. HIMEM.SYS is still required to boot Windows 95. EMM386 and other memory managers, however, are only used by DOS programs. In addition, CONFIG.SYS and AUTOEXEC.BAT settings (aside from HIMEM.SYS) do not affect Windows programs. DOS games, which could not be executed on Windows 3.x, can run inside Windows 95 (games tended to lock up Windows 3.x or cause other problems). As with Windows 3.x, DOS programs that use EGA or VGA graphics modes run in windowed mode ( CGA and text mode programs can continue to run).

On startup, the MS-DOS component in Windows 95 responds to a pressed key by temporarily pausing the default boot process and presenting the DOS boot options menu, allowing the user to continue starting Windows normally, start Windows in safe mode or exit to the DOS prompt. As in previous versions of MS-DOS, there is no 32-bit support and DOS drivers must be loaded for mice and other hardware.

As a consequence of DOS compatibility, Windows 95 has to keep internal DOS data structures synchronized with those of Windows 95. When starting a program, even a native 32-bit Windows program, MS-DOS momentarily executes to create a data structure known as the Program Segment Prefix. It is even possible for MS-DOS to run out of conventional memory while doing so, preventing the program from launching. Windows 3.x allocated ''fixed'' segments in conventional memory first. Since the segments were allocated as fixed, Windows could not move them, which would prevent any more programs from launching.

Microsoft partially removed support for File Control Blocks (an API hold-over of DOS 1.x and CP/M) in Windows 95 OSR2 (OEM Service Release 2). FCB functions can read FAT32 volumes, but not write to them.

User interface

Windows 95 introduced a redesigned shell based around a desktop metaphor; File shortcuts (also known as shell links) were introduced and the desktop was re-purposed to hold shortcuts to applications, files and folders, reminiscent of Mac OS.

In Windows 3.1 the desktop was used to display icons of running applications. In Windows 95, the currently running applications were displayed as buttons on a taskbar across the bottom of the screen. The taskbar also contained a notification area used to display icons for background applications, a volume control and the current time.

The Start menu, invoked by clicking the "Start" button on the taskbar or by pressing the Windows key, was introduced as an additional means of launching applications or opening documents. While maintaining the program groups used by its predecessor Program Manager, it also displayed applications within cascading sub-menus.

The previous File Manager program was replaced by Windows Explorer and the Explorer-based Control Panel and several other special folders were added such as My Computer, Dial-Up Networking, Recycle Bin, Network Neighborhood, My Documents, Recent documents, Fonts, Printers, and My Briefcase among others. AutoRun was introduced for CD drives.

The user interface looked dramatically different from prior versions of Windows, but its design language did not have a special name like ''Metro'', ''Aqua'' or ''Material Design''. Internally it was called "the new shell" and later simply "the shell". The subproject within Microsoft to develop the new shell was internally known as "Stimpy".

In 1994, Microsoft designers Mark Malamud and Erik Gavriluk approached Brian Eno to compose music for the Windows 95 project. The result was the six-second start-up music-sound of the Windows 95 operating system, '' The Microsoft Sound'' and it was first released as a startup sound in May 1995 on Windows 95 May Test Release build 468.

When released for Windows 95 and Windows NT 4.0, Internet Explorer 4 came with an optional Windows Desktop Update, which modified the shell to provide several additional updates to Windows Explorer, including a ''Quick Launch'' toolbar, and new features integrated with Internet Explorer, such as Active Desktop (which allowed Internet content to be displayed directly on the desktop).

Some of the user interface elements introduced in Windows 95, such as the desktop, taskbar, Start menu and Windows Explorer file manager, remained fundamentally unchanged on future versions of Windows.

Technical improvements

Windows 95 included support for 255-character mixed-case long filenames and preemptively multitasked protected-mode 32-bit applications. 16-bit processes were still co-operatively multitasked.

Plug and Play

Windows 95 tried to automate device detection and configuration as much as possible, but could still fall back to manual settings if necessary. During the initial install process of Windows 95, it would attempt to automatically detect all devices installed in the system.

Windows 95 also introduced the Device Manager to indicate which devices were working optimally with correct drivers and configuration and to allow the user to override automatic Plug and Play-based driver installation with manual options or give a choice of several semi-automatic configurations to try to free up resources for devices that still needed manual configuration.

Long file names

32-bit File Access is necessary for the ''long file names'' feature introduced with Windows 95 through the use of the VFAT file system extension. It is available to both Windows programs and MS-DOS programs started from Windows (they have to be adapted slightly, since accessing long file names requires using larger pathname buffers and hence different system calls). Competing DOS-compatible operating systems released before Windows 95 cannot see these names. Using older versions of DOS utilities to manipulate files means that the long names are not visible and are lost if files are moved or renamed and by the copy (but not the original) if the file is copied. During a Windows 95 automatic upgrade of an older Windows 3.1 system, DOS and third-party disk utilities which can destroy long file names are identified and made unavailable. When Windows 95 is started in DOS mode, e.g. for running DOS programs, low-level access to disks is locked out. In case the need arises to depend on disk utilities that do not recognize long file names, such as the MS-DOS 6. x's defrag utility, a program called LFNBACK for backup and restoration of long file names is provided on the CD-ROM, specifically in its \ADMIN\APPTOOLS\LFNBACK directory.

32-bit

Windows 95 followed Windows for Workgroups 3.11 with its lack of support for older, 16-bit x86 processors, thus requiring an Intel 80386

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