Download Windows 95 Operating System and more Summaries Computer science in PDF only on Docsity!
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft,[2]^ and was a significant progression from the company's previous Windows products. During development it was referred to as Windows 4.0 or by the internal codename Chicago. Windows 95 integrated Microsoft's formerly separate MS-DOS and Windows products. It featured significant improvements over its predecessor, Windows 3.1, most notably in the graphical user interface (GUI) and in its relatively simplified "plug-n-play" features. There were also major changes made at lower levels of the operating system, such as moving from a mainly 16-bit architecture to a pre-emptively multitasked 32-bit architecture. In the marketplace, Windows 95 was a major success, and within a year or two of its release had become the most successful operating system ever produced. It also had the effect of driving other major players (including OS/2) out of business, something which would later be used in court against Microsoft. Some three years after its introduction, Windows 95 was succeeded byWindows 98.
Development
The initial design and planning of Windows 95 can be traced back to around March 1992, [3][4][5]^ just after the release of Windows 3.1. At this time Windows for Workgroups 3.1 andWindows NT 3.1 were still in development and Microsoft's plan for the future was focused on Cairo. Cairo would be Microsoft's next- generation operating system based on Windows NT and featuring a new user interface and an object- based file system, but it was not planned to be shipped before 1994 (Cairo would eventually partially ship in July 1996 in the form ofWindows NT 4.0, but 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 were in need of 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). So the development of Windows "Chicago" was started and, as it was planned for a late 1993 release, became known as Windows 93. Initially the decision was made not to include a new user interface, as this was planned for Cairo, and only focus on making installation, configuration, and networking easier. Windows 93 would ship together with MS-DOS 7.0 offering a more integrated experience to the user and making it pointless for other companies to create DOS clones. MS-DOS 7.0 was in development at that time under the code name "Jaguar" and could optionally run on top of a Windows 3.1-based 32-bit protected mode kernel called "Cougar" in order to better compete with DR-DOS. The Chicago project was led by Brad Silverberg, who was at that time, senior vice president of the personal systems division at Microsoft. Microsoft's product plan looked as follows:
Codename Planned release date Description Released as "Janus"[6]^ March 1992 Windows 3. "Astro"[6]^ September 1992 Upgrade to MS-DOS 5.0, adding third party tools to surpass DR-DOS 6.0 in features.
MS-DOS 6.
"Winball"[6]^ Windows for Workgroups 3. "Jaguar"[6]^ June 1993 Next major release of real-mode MS-DOS, better integrating with Windows
(MS-DOS 7.0)
"Cougar"[6]^ June 1993 A 32-bit protected-mode MS-DOS kernel based on Windows' 386 enhanced-mode kernel (Windows 95 VMM) "Panther"[6]^ June 1993 The 32-bit Windows subsystem that could run on top of "Cougar" implementing a subset of Windows NT's Win API, but a superset of the Win32s API. Windows 95 "Rover"[6]^ June 1993 Windows for Mobile Computing, based on "Panther" NT July 1993 A new version of Windows built from the ground up as an operating system for servers and workstations. Windows NT 3. "Cairo" July 1996 Windows NT 4. The first version of Chicago's feature specification was finished on September 30, 1992. Cougar was to become Chicago's kernel.
Beta
Prior to the official release, the American public was given a chance to preview Windows 95 in the Windows 95 Preview Program. For US$19.95, users were sent a set of 3.5-inch floppy diskettes that
Copies of The Times were available for free in the United Kingdom where Microsoft paid for 1.5 million issues (twice the daily circulation at the time). The release included a number of "Fun Stuff" items on the CD, including music videos of Edie Brickell's "Good Times, Bad Times"[10]^ andWeezer's "Buddy Holly", most notably resulting in a sudden skyrocket in the popularity of the video and song "Buddy Holly" that won Weezer a place in MTV Music Video Awards history.[11] Architecture Architectural diagram Windows 95 was designed to be maximally compatible with existing MS-DOS and 16-bit Windows applications and device drivers, while under this constraint offering a more stable and better performing system.[12][13]^ Architecturally, Windows 95 can be considered an evolution ofWindows for Workgroups' 386 enhanced mode. The lowest level of the operating system is formed by a large number of virtual device drivers (VxDs) running in 32-bit protected mode and one or more virtual DOS machines running in virtual 8086 mode. The virtual device drivers can be responsible for handling physical devices (such as video and network cards), emulating virtual devices used by the virtual machines, or providing various system services. The three most important virtual device drivers are: 32-bit Windows applications are each assigned their own memory segment, which can be adjusted to any size the user wishes and memory outside the segment cannot be accessed by an application. This eliminated the use of fixed 64k segments, which were a serious handicap in DOS and Windows 3.x and also caused stability issues in the latter because of applications sometimes overwriting others' segments. If a Windows 3.x application crashes, it can knock out surrounding processes, but 32-bit apps will not harm anything else if they crash. Virtual Machine Manager The Virtual Machine Manager (VMM32.VXD) can be considered the kernel of Windows 95 and is responsible for tasks such as memory management, event and interrupt handling, loading and initialization of virtual device drivers, the creation of new virtual machines, and scheduling of threads. Configuration Manager The Configuration Manager (CONFIGMG) is responsible for implementing Plug and Play functionality. It detects devices in the system using several bus enumerators , monitors the
system for changes to the hardware configuration. It is responsible for assigning various resources (I/O ports, IRQs, DMA channels, and memory) to the devices in a conflict free fashion. Installable File System Manager (Input/Output Subsystem) The Installable File System Manager coordinates the access to various file systems. Windows 95 ships with support for FAT16, and in later releases FAT32, file systems (VFAT), ISO 9660 (CDFS), and several network redirectors. A dynamically sized disk buffer is provided by VCACHE. In the Block I/O Subsystem , requests are scheduled by the Input/Output Supervisor. Access to the disk is performed by a port driver , or in the case of a SCSI device, by a miniport driver working atop the SCSI layer. Like Windows for Workgroups running with 32-bit file (based on IFSHLP.SYS) and disk access enabled, I/O operations can be handled entirely in 32-bit protected mode, bypassingMS- DOS and the BIOS, giving a significant performance improvement. 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 port driver can access it through MS-DOS. The Win32 API is implemented by three modules, each consisting of a 16-bit and a 32- bit component: Kernel Kernel (KRNL386.EXE, KERNEL32.DLL, and VWIN32.VXD) provides high level access to functions such as memory and process management, and access to the file system. User User (USER.EXE and USER32.DLL) is responsible for managing and drawing the various user interface components, such as windows, menus, and buttons. GDI The Graphics Device Interface (GDI.EXE and GDI32.DLL) is responsible for drawing graphics in a device-independent way. User interface
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 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. The program is in the \ADMIN\APPTOOLS\LFNBACK directory of the Windows 95 CD- ROM.
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 (or compatible). While the OS kernel is 32-bit, much code (especially for the user interface) remained 16-bit for performance reasons as well as development time constraints (much of W95's UI code was recycled from Windows 3.1). This had a rather detrimental effect on system stability and led to frequent application crashes. The introduction of 32-bit File Access in Windows for Workgroups 3. meant that 16-bit real mode MS-DOS is not used for managing the files while Windows is running, and the earlier introduction of the 32-bit Disk Access means that the PC BIOS is not used for managing hard disks. This essentially reduces MS-DOS to the role of a boot loader for the protected- mode Windows kernel. DOS can be used for running old-style drivers for compatibility, but Microsoft discourages using them, as this prevents proper multitasking and impairs system stability.Control Panel allows a user to see what MS-DOS components are used by the system; optimal performance is achieved when they are bypassed. The Windows kernel uses MS-DOS style real-mode drivers in Safe Mode, which exists to allow a user to fix problems relating to loading native, protected-mode drivers. Internet Explorer Windows 95 originally shipped without Internet Explorer, and the default network installation did not install TCP/IP, the network protocol used on the Internet. At the release date of Windows 95, Internet Explorer 1.0 was available, but only in the Plus! add-on pack for Windows 95, which was a separate product. The Plus! Pack did not reach as many retail consumers as the operating system itself (it was mainly advertised for its add-ons such as themes and better disk compression) but was usually included in pre- installed (OEM) sales, and at the time of Windows 95 release, the web was being browsed mainly with a variety of early web browsers such as Netscape (promoted by products such as Internet in a Box). Windows 95 OEM Service Release 1 was the first release of Windows to include Internet Explorer (version 2.0) with the OS. While there was no uninstaller, it could be deleted easily if the user so desired. OEM Service Release 2 included Internet Explorer 3. The installation of Internet Explorer 4 on Windows 95 (or the OSR2.5 version preinstalled on a computer) gave
Windows 95 active desktop and browser integration into Windows Explorer, known as the Windows Desktop Update. The CD version of the last release of Windows 95, OEM Service Release 2.5 (Version 4.00.950C), includes Internet Explorer 4, and installs it after Windows 95's initial setup and first boot is complete. Only the 4.x series of the browser contained the Windows Desktop Update features, so anyone wanting the new shell had to install IE4 with the desktop update before installing a newer version of Internet Explorer. The last version of Internet Explorer supported on Windows 95 is Internet Explorer 5.5 which was released in 2000. Windows 95 shipped with Microsoft's own dial-up online service called The Microsoft Network. Editions A number of different editions of Windows 95 have been released. Only the original release was sold as a shrink-wrapped product, later editions were provided only to computer original equipment manufacturers (OEMs) for installation on new PCs. For this reason these editions are known as OEM Service Releases ( OSR ). Together with the introduction of Windows 95, Microsoft released the Microsoft Plus! for Windows 95 pack, which contained a number of optional components for high-end (486) multimedia PCs, including Internet Explorer, DriveSpace, and additional themes. Microsoft initially indicated to make updates available to Windows 95 every 6 months in the form of service packs. The growing availability of Internet access meant that Windows updates could now be downloaded from Microsoft directly. The first service pack was made available half a year after the original release and fixed a number of small bugs. The second service pack mainly introduced support for new hardware. Most notably support for hard drives larger than 2 GB in the form of the FAT32 file system. This release was never made available to end-users directly and was only sold through OEMs with the purchase of a new PC. A full third service pack was never released, but two smaller updates to the second were released in the form of a USB Supplement (OSR 2.1) and the Windows Desktop Update (OSR 2.5). Both were available as stand- alone updates and as updated disc images shipped by OEMs. OSR 2. was notable for featuring a number of changes to the Windows Explorer, integrating it with Internet Explorer 4.0—this version of the Explorer looks very similar to the one featured in Windows 98.
