The story of Windows begins with a very different operating system, developed by Microsoft for the first IBM personal computer and referred to as MS-DOS or PC-DOS. The initial version, DOS 1.0, was released in August 1981. It consisted of 4000 lines of assembly language source code and ran in 8 Kbytes of memory using the Intel 8086 microprocessor.
When IBM developed a hard disk-based personal computer, the PC XT, Microsoft developed DOS 2.0, released in 1983. It contained support for the hard disk and provided for hierarchical directories. Heretofore, a disk could contain only one directory of files, supporting a maximum of 64 files. While this was adequate in the era of floppy disks, it was too limited for a hard disk, and the single-directory restriction was too clumsy. This new release allowed directories to contain subdirectories as well as files. The new release also contained a richer set of commands embedded in the operating system to provide functions that had to be performed by external programs provided as utilities with release 1. Among the capabilities added were several UNIX-like features, such as I/O redirection, which is the ability to change the input or output identity for a given application, and background printing. The memory-resident portion grew to 24 Kbytes.
When IBM announced the PC AT in 1984, Microsoft introduced DOS 3.0. The AT contained the Intel 80286 processor, which provided extended addressing and memory protection features. These were not used by DOS. To remain compatible with previous releases, the operating system simply used the 80286 as a "fast 8086." The operating system did provide support for new keyboard and hard disk peripherals. Even so, the memory requirement grew to36 Kbytes. There were several notable upgrades to the 3.0 release. DOS 3.1, released in 1984, contained support for networking of PCs. The size of the resident portion did not change; was achieved by increasing the amount of the operating system that could be swapped. DOS 3.3,released in 1987, provided support for the new line of IBM machines, the PS/2. Again, thisrelease did not take advantage of the processor capabilities of the PS/2, provided by the 80286 and the 32-bit 80386 chips. The resident portion at this stage had grown to a minimum of 46Kbytes, with more required if certain optional extensions were selected.
By this time, DOS was being used in an environment far beyond its capabilities. The introduction of the 80486 and then the Intel Pentium chip provided power and features that simply could not be exploited by the simple-minded DOS. Meanwhile, beginning in the early 1980s, Microsoft began development of a graphical user interface (GUI) that would be interposed between the user and DOS. Microsoft's intent was to compete with Macintosh, whose operating system was unsurpassed for ease of use. By 1990, Microsoft had a version of the GUI, known as Windows 3.0, which incorporated some of the user friendly features of Macintosh. However, it was still hamstrung by the need to run on top of DOS.
After an abortive attempt by Microsoft to develop with IBM a next-generation operatingsystem, which would exploit the power of the new microprocessors and which would incorporate the ease-of-use features of Windows, Microsoft struck out on its own and developed a new operating system from the ground up, Windows NT. Windows NT exploits the capabilities of contemporary microprocessors and provides multitasking in a single-user or multiple-user environment.
The first version of Windows NT (3.1) was released in 1993, with the same GUI as Windows 3.1, another Microsoft operating system (the follow-on to Windows 3.0). However, NT 3.1 was a new 32-bit operating system with the ability to support older DOS and Windows applications as well as provide OS/2 support
After several versions of NT 3.x, Microsoft released NT 4.0. NT 4.0 has essentially the same internal architecture as 3.x. The most notable external change is that NT 4.0 provides the same user interface as Windows 95. The major architectural change is that several graphics components that ran in user mode as part of the Win32 subsystem in 3.x have been moved intothe Windows NT Executive, which runs in kernel mode. The benefit of this change is to speed up
the operation of these important functions. The potential drawback is that these graphics functions now have access to low-level system services, which could impact the reliability of the operating system
In 2000, Microsoft introduced the next major upgrade, now called Windows 2000. Again, the underlying Executive and kernel architecture is fundamentally the same as in NT 4.0, but new features have been added. The emphasis in Windows 2000 is the addition of services and functions to support distributed processing. The central element of Windows 2000's new features is Active Directory, which is a distributed directory service able to map names of arbitrary objects to any kind of information about those objects.
One final general point to make about Windows 2000 is the distinction between Windows 2000 Server and Windows 2000 desktop. In essence, the kernel and executive architecture and services remain the same, but Server includes some services required to use as a network server
In 2001, the latest desktop version of Windows was released, known as Windows XP. Both home PC and business workstation versions of XP are offered. Also in 2001, a 64-bit version of XP was introduced. In 2003, Microsoft introduced a new server version, known as Windows Server 2003; both 32-bit and 64 bit versions are available. The 64-bit versions of XP and Server 2003 are designed specifically for the 64-bit Intel Itanium hardware.
Courtesy
http://avellano.fis.usal.es/~lalonso/amp_inf/windows.pdf
