I am using Windows XP.
Current Versions:
Windows Vista, for home and business desktops and portable computers
Windows Vista Starter Much like Windows XP Starter Edition, this edition will be limited to emerging markets such as Colombia, India, Thailand, and Indonesia, mainly to offer a legal alternative to using unauthorized copies. It will not be available in the United States, Canada, Europe, or Australia.
Windows Vista Home Basic Similar to Windows XP Home Edition, Home Basic is intended for budget users not requiring advanced media support for home use. The Windows Aero theme with translucent effects will not be included with this edition.
Windows Vista Home Premium Containing all features from Home Basic, this edition will also support more advanced features aimed for the home market segment, such as HDTV support and DVD authoring. Extra premium games, mobile and tablet PC, Network Projector, Touch Screen, and auxiliary display (via Windows Side Show) support.
Windows Vista Business Comparable to Windows XP Professional and Windows XP Tablet PC Edition, Windows Vista Business Edition is aimed at the business market. Includes all the features of Home Premium with the exception of Windows Media Center and related technologies, Parental Controls, and Windows DVD and Movie Maker HD.
Windows Vista Enterprise This edition is aimed at the enterprise segment of the market, and is a superset of the Business edition. Additional features include multilingual user interface support, BitLocker Drive Encryption, and UNIX application support. This edition will not be available through retail or OEM channels
Windows Vista Ultimate This edition combines all the features of the Home Premium and Enterprise editions, a game performance tweaker (WinSAT), and "Ultimate Extras". On January 7, 2007, at CES, Microsoft began to announce what some of these Ultimate Extras will be.
Windows Server 2003 R2 for servers
Windows Server 2003 R2, Standard Edition
Windows Server 2003 R2, Enterprise Edition
Windows Server 2003 R2, Datacenter Edition
Windows XP Embedded, for embedded systems requiring parts of the Windows XP infrastructure
Windows Fundamentals for Legacy PCs, a low-end version of Windows XP that is intended to be a thin-client that works with older hardware.
Windows Embedded CE 6.0, for embedded systems (not based on the Windows NT kernel)
Past Versions:
Windows XP for desktops and laptops (notebooks)
Windows XP Starter Edition, for new computer users in developing countries
Windows XP Home Edition, for home desktops and laptops
Windows XP Home Edition N, as above, but without a default installation of Windows Media Player, as mandated by an EU ruling
Windows XP Professional Edition, for business and power users (Version number: NT 5.1.2600)
Windows XP Professional Edition N, as above, but without a default installation of Windows Media Player, as mandated by an EU ruling
Windows XP Professional x64 Edition, for PCs with 64-bit processors (based on Windows Server 2003)
Windows XP Tablet PC Edition, for notebooks with a touch screen or a pen-sensitive screen
Windows XP Media Center Edition for desktops and notebooks with an emphasis on audio, video, and PVR capability, in at least three flavors:
Windows XP Media Center Edition 2002 with SP2
Windows XP Media Center Edition 2004 with SP2
Windows XP Media Center Edition 2005
Portable Media Center for Digital Media Players
Windows Server 2003 for servers
Small Business Server for first server installations (up to 2 processors)
Web Edition for basic Web serving (up to 2 processors)
Standard Edition for smaller server applications that don't require clustering (up to 4 processors)
Enterprise Edition for larger server applications, and clustering (up to 8 processors)
Datacenter Edition for mainframe like servers (up to 128 processors)
Storage Server for Network Attached Storage Devices
NT Kernel-Based
1993 August - Windows NT 3.1
1994 September - Windows NT 3.5
1995 June - Windows NT 3.51 (Version number: NT 3.5.1057)
1996 July 29 - Windows NT 4.0 - the last version which ran on RISC architectures like DEC Alpha, MIPS and PowerPC. Later versions concentrated on x86-based hardware and - mainly as server OSs - the IA-64 line of CPUs. (Version number: NT 4.0.1381)
2000 February 17 - Windows 2000 (Version number: NT 5.0.2195)
2001 October 25 - Windows XP 64-bit Edition - A version of Windows XP roughly analogous to Windows XP Professional for Intel's IA-64 (Itanium) line of CPUs. It was discontinued in early 2005 after manufacturers stopped shipping Itanium systems marketed as 'workstations'.
CE-based
Windows CE for embedded systems including Consumer Electronics products (note: CE is a different operating system from DOS and Windows NT/2000/XP, and Microsoft makes the source code available)
Windows Mobile for smart phones and PDAs (a version of Windows CE)
1996 November - Windows CE 1.0
Windows 98 Second Edition box shot
Windows 1.0 box shot
1997 November - Windows CE 2.0
1998 July - Windows CE 2.1
1998 October - Windows CE 2.11 for the Hand-held PC
1999 August - Windows CE 2.12
2000 July - Windows CE 3.0
DOS-Based
2000 June 19 - Windows Me (Version number: 4.90.3000 (Security Version 4.90.3000A))
1999 May 5 - Windows 98 Second Edition (Version number: 4.10.2222 or 4.10.2222A (Security Version 4.10.2222C))
1998 June 25 - Windows 98 (Version number: 4.10.1998 (Security Version 4.10.1998A))
1997 August 27 - Windows 95 OSR2.5 (Version number: 4.00.1214 (also listed as 4.0.950C))
1997 August 27 - Windows 95 OSR2.1 (Version number: 4.00.1212 (also listed as 4.0.950B))
1996 August 24 - Windows 95 OSR2 (Version number: 4.00.1111 (also listed as 4.0.950B))
1995 December 31 - Windows 95 SP1 (Version number: 4.00.950A)
1995 August 24 - Windows 95 (Version number: 4.00.950)
1993 October - Windows 3.2 This Version of Windows was only released in simplified Chinese.
1993 November - Windows for Workgroups 3.11
1992 October - Windows for Workgroups 3.1
1992 August - Windows 3.1
1990 May 22 - Windows 3.0
1987 December 9 - Windows 2.0
1985 November 20 - Windows 1.0