Windows XP is an operating system that was produced by Microsoft for use on personal computers, including home and business desktops, laptops, and media centers. It was first released to computer manufacturers on August 24, 2001, and is the most popular version of Windows, based on installed user base. The name "XP" is short for "eXPerience."
Windows XP was the successor to both Windows 2000 and Windows Me, and was the first consumer-oriented operating system produced by Microsoft to be built on the Windows NT kernel and architecture. Windows XP was released for retail sale on October 25, 2001, and over 400 million copies were in use in January 2006, according to an estimate in that month by an IDC analyst. It was succeeded by Windows Vista, which was released to volume license customers on November 8, 2006, and worldwide to the general public on January 30, 2007. Direct OEM and retail sales of Windows XP ceased on June 30, 2008. Microsoft continued to sell Windows XP through their System Builders (smaller OEMs who sell assembled computers) program until January 31, 2009. XP may continue to be available as these sources run through their inventory or by purchasing Windows 7 Ultimate, Windows 7 Pro, Windows Vista Ultimate or Windows Vista Business, and then downgrading to Windows XP.
The most common editions of the operating system were Windows XP Home Edition, which was targeted at home users, and Windows XP Professional, which offered additional features such as support for Windows Server domains and two physical processors, and was targeted at power users, business and enterprise clients. Windows XP Media Center Edition has additional multimedia features enhancing the ability to record and watch TV shows, view DVD movies, and listen to music. Windows XP Tablet PC Edition was designed to run stylus applications built using the Tablet PC platform.
Windows XP was eventually released for two additional architectures, Windows XP 64-bit Edition for IA-64 (Itanium) processors and Windows XP Professional x64 Edition for x86-64. There is also Windows XP Embedded, a component version of the Windows XP Professional, and editions for specific markets such as Windows XP Starter Edition. By mid 2009, a manufacturer revealed the first Windows XP powered cellular telephone.
The NT-based versions of Windows, which are programmed in C, C++, and assembly, are known for their improved stability and efficiency over the 9x versions of Microsoft Windows. Windows XP presented a significantly redesigned graphical user interface, a change Microsoft promoted as more user-friendly than previous versions of Windows. A new software management facility called Side-by-Side Assembly was introduced to ameliorate the "DLL hell" that plagues 9x versions of Windows. It is also the first version of Windows to use product activation to combat illegal copying. Windows XP had also been criticized by some users for security vulnerabilities, tight integration of applications such as Internet Explorer 6 and Windows Media Player, and for aspects of its default user interface. Later versions with Service Pack 2, Service Pack 3, and Internet Explorer 8 addressed some of these concerns.
During development, the project was codenamed "Whistler", after Whistler, British Columbia, as many Microsoft employees skied at the Whistler-Blackcomb ski resort
Windows XP featured a new task-based graphical user interface. The Start menu and Taskbar were updated and many visual effects were added, including:
- A translucent blue selection rectangle in Explorer
- Drop shadows for icon labels on the desktop
- Task-based sidebars in Explorer windows ("common tasks")
- The ability to group the taskbar buttons of the windows of one application into one button
- The ability to lock the taskbar and other toolbars to prevent accidental changes
- The highlighting of recently added programs on the Start menu
- Shadows under menus (Windows 2000 had shadows under mouse pointers, but not menus)
In addition to the included Windows XP themes, there is one previously unreleased theme with a dark blue taskbar and window bars similar to Windows Vista titled "Royale Noir" available for download, albeit unofficially. Microsoft officially released a modified version of this theme as the "Zune" theme, to celebrate the launch of its Zune portable media player in November 2006. The differences are only visual with a new glassy look along with a black taskbar instead of dark blue and an orange start button instead of green. Additionally, the Media Center "Energy Blue" theme, which was included in the Media Center editions, is also available to download for use on all Windows XP editions.
The default wallpaper, Bliss, is a BMP photograph of a landscape in the Napa Valley outside Napa, California, with rolling green hills and a blue sky with stratocumulus and cirrus clouds.
The Windows 2000 "classic" interface can be used instead if preferred. Several third party utilities exist that provide hundreds of different visual styles.
 New and updated featuresWindows XP introduced several new features to the Windows line, including:
- GDI+ graphics subsystem
- Start Menu and Taskbar improvements
- A number of new features in Windows Explorer
- Faster start-up, logon and logoff and hibernation sequences.
- The ability to discard a newer device driver in favor of the previous one (known as driver rollback), should a driver upgrade not produce desirable results.
- A new, arguably more user-friendly interface, including the framework for developing themes for the desktop environment 
- Fast user switching, which allows a user to save the current state and open applications of their desktop and allow another user to log on without losing that information 
- The ClearType font rendering mechanism, which is designed to improve text readability on liquid crystal display (LCD) and similar monitors 
- Remote Desktop functionality, which allows users to connect to a computer running Windows XP Pro from across a network or the Internet and access their applications, files, printers, and devices.
- Support for most DSL modems and IEEE 802.11 connections, as well as networking over FireWire, and Bluetooth.
- Improved application compatibility compared to Windows 2000
 EditionsMedia Center Extender capabilities. Unlike the Home and Professional edition, it was never made available for retail purchase, and was typically either sold through OEM channels, or was preinstalled on computers that were typically marketed as "media center PCs".
Two different 64-bit editions were made available, one designed specifically for Itanium-based workstations, which was introduced in 2001 around the same time as the Home and Professional editions, but was discontinued a few years later when vendors of Itanium hardware stopped selling workstation-class machines due to low sales. The other, called Windows XP Professional x64 Edition, supports the x86-64 extension. x86-64 was implemented first by AMD as "AMD64", found in AMD's Opteron and Athlon 64 chips, and later implemented by Intel as "Intel 64" (formerly known as IA-32e and EM64T), found in Intel's Pentium 4 and later chips.
Windows XP Tablet PC Edition was produced for a class of specially designed notebook/laptop computers called tablet PCs. It is compatible with a pen-sensitive screen, supporting handwritten notes and portrait-oriented screens.
Windows XP Embedded, an edition for specific consumer electronics, set-top boxes, kiosks/ATMs, medical devices, arcade video games, point-of-sale terminals, and Voice over Internet Protocol (VoIP) components. In July 2006, Microsoft released Windows Fundamentals for Legacy PCs, a thin client version of Windows XP Embedded which targets older machines (as early as the original Pentium). It is only available to Software Assurance customers. It is intended for corporate customers who would like to upgrade to Windows XP to take advantage of its security and management capabilities, but can't afford to purchase new hardware.
 Editions for specific marketsWindows XP Starter Edition is a lower-cost edition of Windows XP available in Thailand, Indonesia, Russia, India, Colombia, Brazil, Argentina, Peru, Bolivia, Chile, Mexico, Ecuador, Uruguay and Venezuela. It is similar to Windows XP Home, but is limited to low-end hardware, can only run 3 programs at a time, and has some other features either removed or disabled by default. Each country's edition is also customized for that country, including desktop backgrounds of popular locations, localized help features for those who may not speak English, and other default settings designed for easier use than typical Windows XP installations. The Malaysian version, for example, contains a desktop background of the Kuala Lumpur skyline.
In March 2004, the European Commission fined Microsoft €497 million (US$603 million) and ordered the company to provide a version of Windows without Windows Media Player. The Commission concluded that Microsoft "broke European Union competition law by leveraging its near monopoly in the market for PC operating systems onto the markets for work group server operating systems and for media players". After unsuccessful appeals in 2004 and 2005, Microsoft reached an agreement with the Commission where it would release a court-compliant version, Windows XP Edition N. This version does not include the company's Windows Media Player but instead encourages users to pick and download their own media player. Microsoft wanted to call this version Reduced Media Edition, but EU regulators objected and suggested the Edition N name, with the N signifying "not with Media Player" for both Home and Professional editions of Windows XP. Because it is sold at the same price as the version with Windows Media Player included, Dell, Hewlett-Packard, Lenovo and Fujitsu Siemens have chosen not to stock the product. However, Dell did offer the operating system for a short time. Consumer interest has been low, with roughly 1,500 units shipped to OEMs, and no reported sales to consumers.
In December 2005, the Korean Fair Trade Commission ordered Microsoft to make available editions of Windows XP and Windows Server 2003 that do not contain Windows Media Player or Windows Messenger. Like the European Commission decision, this decision was based on the grounds that Microsoft had abused its dominant position in the market to push other products onto consumers. Unlike that decision, however, Microsoft was also forced to withdraw the non-compliant versions of Windows from the South Korean market. This decision resulted in Microsoft's releasing "K" and "KN" variants of the Home and Professional editions in August 2006.
That same year, Microsoft also released two additional editions of Windows XP Home Edition directed towards subscription-based and pay-as-you-go pricing models. These editions, released as part of Microsoft's FlexGo initiative, are used in conjunction with a hardware component to enforce time limitations on the usage of Windows. Its target market is emerging economies such as Brazil and Vietnam.
 LanguagesWindows XP was available in many languages. In addition, MUI packs and Language Interface Packs translating the user interface were also available for certain languages.
 ATMs and VendorsAutomated teller machine (ATM) vendors Wincor Nixdorf, NCR Corporation and Diebold Incorporated have all adopted Microsoft Windows XP as their migration path from OS/2. Wincor Nixdorf, who has been pushing for standardization for many years, began shipping ATMs with Windows when they first arrived on the scene.
Diebold initially shipped XP Home Edition exclusively, but, following extensive pressure from customer banks to support a common operating system, switched to support XP Professional to match their primary competitor, NCR Corporation and Wincor Nixdorf.
Redbox DVD Vending machines run a modified version of XP designed for the fullscreen User Interface of the Vending Touchscreen and the DVD vending itself.
 Service packsMicrosoft occasionally releases service packs for its Windows operating systems to fix problems and add features. Each service pack is a superset of all previous service packs and patches so that only the latest service pack needs to be installed, and also includes new revisions. However if you still have the earliest version of Windows XP on Retail CD (without any service packs included), you will need to install SP1a or SP2, before SP3 can be installed. Older service packs need not be manually removed before application of the most recent one. Windows Update "normally" takes care of automatically removing unnecessary files.
The service pack details below only apply to the 32-bit editions. Windows XP Professional x64 Edition was based on Windows Server 2003 Service Pack 1 and claimed to be "SP1" in system properties from the initial release. It is updated by the same service packs and hotfixes as the x64 edition of Windows Server 2003.
 Service Pack 1RTM security fixes and hot-fixes, compatibility updates, optional .NET Framework support, enabling technologies for new devices such as Tablet PCs, and a new Windows Messenger 4.7 version. The most notable new features were USB 2.0 support and a Set Program Access and Defaults utility that aimed at hiding various middleware products. Users can control the default application for activities such as web browsing and instant messaging, as well as hide access to some of Microsoft's bundled programs. This utility was first brought into the older Windows 2000 operating system with its Service Pack 3. This Service Pack supported SATA and hard drives that were larger than 137GB (48-bit LBA support) by default. The Microsoft Java Virtual Machine, which was not in the RTM version, appeared in this Service Pack. Support for IPv6 was also introduced in this Service Pack.
On February 3, 2003, Microsoft released Service Pack 1a (SP1a). This release removed Microsoft's Java virtual machine as a result of a lawsuit with Sun Microsystems.
 Service Pack 2 with an emphasis on security. Unlike the previous service pack, SP2 added new functionality to Windows XP, such as WPA encryption compatibility and improved Wi-Fi support (with a wizard utility), a pop-up ad blocker for Internet Explorer 6, and Bluetooth support. The new welcome screen during the kernel boot removes the subtitles "Professional", "Home Edition" and "Embedded" since Microsoft introduced new Windows XP editions prior to the release of SP2. The green loading bar in Home Edition and the yellow one in Embedded were replaced with the blue bar, seen in Professional and other versions of Windows XP, making the boot-screen of operating systems resemble each other. Colors in other areas, such as Control Panel and the Help and Support tool, remained as before.
Service Pack 2 also added new security enhancements (codenamed "Springboard"), which included a major revision to the included firewall that was renamed to Windows Firewall and became enabled by default, Data Execution Prevention, which can be weakly emulated,[clarification needed] gains hardware support in the NX bit that can stop some forms of buffer overflow attacks. Also raw socket support is removed (which supposedly limits the damage done by zombie machines). Additionally, security-related improvements were made to e-mail and web browsing. Windows XP Service Pack 2 includes the Windows Security Center, which provides a general overview of security on the system, including the state of antivirus software, Windows Update, and the new Windows Firewall. Third-party anti-virus and firewall applications can interface with the new Security Center.
 Service Pack 2bIn August 2006, Microsoft released updated installation media for Windows XP SP2 and Windows Server 2003 SP1 to contain a patch that requires ActiveX controls to require manual activation in accordance with a patent held by Eolas. Since then, the technology was licensed by Microsoft, and Service Pack 3 and later versions do not include this update.
 Service Pack 2cOn August 10, 2007, Microsoft announced a minor update to Service Pack 2, called Service Pack 2c (SP2c). The update fixes the issue of the diminishing number of available product keys for Windows XP. This update was only available to system builders from their distributors in Windows XP Professional and Windows XP Professional N operating systems. SP2c was released in September 2007.
 Service Pack 3Windows XP Service Pack 3 (SP3) was released to manufacturing on April 21, 2008, and to the public via both the Microsoft Download Center and Windows Update on May 6, 2008.
It began being automatically pushed out to Automatic Update users on July 10, 2008. A feature set overview which details new features available separately as standalone updates to Windows XP, as well as backported features from Windows Vista has been posted by Microsoft. A total of 1,174 fixes have been included in SP3. Service Pack 3 can be installed on systems with Internet Explorer versions 6, 7 or 8. Internet Explorer 7 and 8 are not included as part of SP3.
 New features in Service Pack 3
- Turns black hole router detection on by default
- Network Access Protection client
- Group Policy support for IEEE 802.1X authentication for wired network adapters.
- Credentials Security Service Provider
- Descriptive Security options in Group Policy/Local Security Policy user interface
- An updated version of the Microsoft Enhanced Cryptographic Provider Module (RSAENH) that is FIPS 140-2 certified (SHA-256, SHA-384 and SHA-512 algorithms)
- Installing without requiring a product key during setup for retail and OEM versions
 Previously released updatesService Pack 3 also incorporated several previously released key updates for Windows XP, which were not included up to SP2 including:
- Windows Imaging Component
- IPSec Simple Policy Update for simplified creation and maintenance of IPSec filters
- Background Intelligent Transfer Service (BITS) 2.5
- MSXML 6.0 SP2 and XMLLite
- Microsoft Management Console 3.0
- Credential Roaming service (Digital Identity Management Service) update
- Remote Desktop Protocol 6.1
- Peer Name Resolution Protocol 2.1
- Network Diagnostics update
- WPA2 Update (KB893357)
- Windows Script 5.7
- Windows Installer 3.1 v2
Windows XP Service Pack 3 is a cumulative update of all previous service packs for XP. The service pack installer checks HKLM\SYSTEM\CurrentControlSet\Control\Windows\CSDVersion registry key to see if has a value greater than or equal to 0x100, and if it does it will allow the update to proceed. Otherwise it will prompt to install either XP SP1 or SP2. Since SP1 is no longer available for full download, it would need to be downloaded using Windows Update. The other option is to manually change the registry key, in essence fooling the installer into thinking SP1 is already installed.
However, it is possible to slipstream SP3 into the Windows XP setup files at any service pack level—including the original RTM version—without any errors or issues. Slipstreaming SP3 into Windows XP Media Center Edition 2005 is not supported.
Service Pack 3 contains updates to the operating system components of Windows XP Media Center Edition (MCE) and Windows XP Tablet PC Edition, and security updates for .NET Framework version 1.0, which is included in these Windows XP SKUs. However, it does not include update rollups for the Windows Media Center application in Windows XP MCE 2005. SP3 also omits security updates for Windows Media Player 10, although the player is included in Windows XP MCE 2005. The Address Bar DeskBand on the Taskbar is no longer included due to legal restrictions. It also removed the Energy Star logo from the ScreenSaver tab of the Display properties, leaving a very noticeable blank space next to the link to enter the Power Management control panel.
 Physical memory limitsMaximum limits on physical memory (RAM) that Windows XP can address vary depending on both the Windows version and between 32-bit and 64-bit versions. The following table specifies the maximum physical memory limits supported:
|Version||Limit in 32-bit Windows||Limit in 64-bit Windows|
|Windows XP Professional||4 GB||128GB|
|Windows XP Home Edition||4 GB||N/A|
|Windows XP Media Center Edition||4 GB||N/A|
|Windows XP Tablet PC Edition||4 GB||N/A|
|Windows XP Starter Edition||512 MB||N/A|
 Multiprocessor limitsThe maximum quantity of physical processors of a PC that Windows XP supports is: two for Professional, one for Home Edition. This count refers to the entire physical processor socket, not the individual cores of a multi-core processor.
 Support lifecycleSupport for Windows XP without a service pack ended on September 30, 2004 and support for Windows XP Service Pack 1 and 1a ended on October 10, 2006.
Windows XP Service Pack 2 was retired on July 13, 2010, almost six years after its general availability. In accordance with Microsoft's posted timetable, the company stopped general licensing of Windows XP to OEMs and terminated retail sales of the operating system on June 30, 2008, 17 months after the release of Windows Vista. However, an exception was announced on April 3, 2008, for OEMs installing to ultra low-cost PCs (ULCPCs) until one year after the availability of Windows 7 (October 22, 2010)
On April 14, 2009, Windows XP and its family of operating systems were moved from Mainstream Support to the Extended Support phase as it marks the progression of the legacy operating system through the Microsoft Support Lifecycle Policy. During the Extended Support Phase, Microsoft will continue to provide security updates every month for Windows XP; however, free technical support, warranty claims, and design changes are no longer being offered.
On April 8, 2014, all Windows XP support, including security updates and security-related hotfixes, will be terminated.
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 Security issuesWindows XP has been criticized for its susceptibility to malware, computer viruses, trojan horses, and computer worms. Security issues are compounded by the fact that users, by default, receive an administrator account that provides unrestricted access to the underpinnings of the system. If the administrator's account is broken into, there is no limit to the control that can be asserted over the compromised PC.
Windows, with its large market share, has historically been a tempting target for virus creators. Security holes are often invisible until they are exploited, making preemptive action difficult. Microsoft has stated that the release of patches to fix security holes is often what causes the spread of exploits against those very same holes. Hackers exploit these holes by figuring out what problems the patches fix, and then proceed to launch attacks against unpatched systems. Microsoft recommends that all systems have automatic updates turned on to prevent a system from being attacked by an unpatched bug, but some business IT departments need to test updates before deployment across systems to predict compatibility issues with custom software and infrastructure. This deployment turn-around time also lengthens the time that systems are left unsecured in the event of a released software exploit.
When Windows XP was released in 2001, it came with Internet Explorer 6, which is now insecure and outdated. Since February 2010, Microsoft has urged all users to upgrade to Internet Explorer 8, which has better security.
 Integration of operating system featuresIn light of the United States v. Microsoft case which resulted in Microsoft being found liable for abusing its operating system monopoly to overwhelm competition in other markets, Windows XP has drawn fire for integrating user applications such as Windows Media Player and Windows Messenger into the operating system, as well as for its close ties to the .NET Passport (now Windows Live ID) service.
 Backward compatibilityMigrating from Windows 9x to XP can be an issue for users dependent upon MS-DOS. Although XP comes with the ability to run DOS programs in a virtual DOS machine, it still has trouble running many old DOS programs. This is largely because it is a Windows NT system and does not use DOS as a base OS, and that the Windows NT architecture is different from Windows 9x. Some DOS programs that cannot run natively on XP, notably programs that rely on direct access to hardware, can be run in emulators, such as DOSBox or virtual machines, like VMware, Virtual PC, or VirtualBox. This also applies to programs that only require direct access to certain common emulated hardware components, like memory, keyboard, and serial ports.
 Product activation and verification
 Product activationIn an attempt to reduce piracy, Windows XP introduced product activation. Activation required the computer or the user to activate with Microsoft (either online or over the phone) within a certain amount of time in order to continue using the operating system. If the user's computer system ever changes — for example, if two or more relevant components of the computer itself are upgraded — Windows will return to the unactivated state and will need to be activated again within a defined grace period. If a user tried to reactivate too frequently, the system will refuse to activate online. The user must then contact Microsoft by telephone to obtain a new activation code.
However, activation only applied to retail and "system builder" (intended for use by small local PC builders) copies of Windows. "Royalty OEM" (used by large PC vendors) copies are instead locked to a special signature in the machine's BIOS (and will demand activation if moved to a system whose motherboard does not have the signature) and volume license copies do not require activation at all. Predictably, this led to pirates simply using volume license copies with volume license keys that were widely distributed on the Internet.
 Product key testingIn addition to activation, Windows XP service packs will refuse to install on Windows XP systems with product keys known to be widely used in unauthorized installations. These product keys are either intended for use with one copy (for retail and system builder), for one OEM (for BIOS locked copies) or to one company (for volume license copies) and are included with the product. However a number of volume licence product keys (which as mentioned above avoid the need for activation) were posted on the Internet and were then used for a large number of unauthorized installations. The service packs contain a list of these keys and will not update copies of Windows XP that use them.
Microsoft developed a new key verification engine for Windows XP Service Pack 2 that could detect illicit keys, even those that had never been used before. After an outcry from security consultants who feared that denying security updates to illegal installations of Windows XP would have wide-ranging consequences even for legal owners, Microsoft elected to disable the new key verification engine. Service Pack 2 only checks for the same small list of commonly used keys as Service Pack 1. This means that while Service Pack 2 will not install on copies of Windows XP which use the older set of copied keys, those who use keys which have been posted more recently may be able to update their systems.
 Windows Genuine AdvantageWindows Media Player 11, Windows Defender, Microsoft Office 2007 and certain updates. In late 2007, Microsoft removed the WGA verification from the installer for Internet Explorer 7 saying that the purpose of the change was to make IE7 available to all Windows users.
If the license key is judged not genuine, it displays a nag screen at regular intervals asking the user to buy a license from Microsoft. In addition, the user's access to Microsoft Update is restricted to critical security updates, and as such, new versions of enhancements and other Microsoft products will no longer be able to be downloaded or installed.
On August 26, 2008, Microsoft released a new WGA activation program that displays a plain black desktop background for computers failing validation. The background can be changed, but reverts after 1 hour.
Common criticisms of WGA have included its description as a "Critical Security Update", causing Automatic Updates to download it without user intervention on default settings, its behavior compared to spyware of "phoning home" to Microsoft every time the computer is connected to the Internet, the failure to inform end users what exactly WGA would do once installed (rectified by a 2006 update), the failure to provide a proper uninstallation method during beta testing (users were given manual removal instructions that did not work with the final build), and its sensitivity to hardware changes which cause repeated need for reactivation in the hands of some developers. Also if the user has no connection to the Internet or a phone, it will be difficult to activate it normally.
Strictly speaking, neither the download nor the install of the Notifications is mandatory; the user can change their Automatic Update settings to allow them to choose what updates may be downloaded for installation. If the update is already downloaded, the user can choose not to accept the supplemental EULA provided for the Notifications. In both cases, the user can also request that the update not be presented again. Newer Critical Security Updates may still be installed with the update hidden. However this setting will only have effect on the existing version of Notifications, so it can appear again as a new version. In 2006, California resident Brian Johnson attempted to bring a class action lawsuit against Microsoft, on grounds that Windows Genuine Advantage Notifications violated the spyware laws in the state; the lawsuit was dismissed in 2010.
 License and media types
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Each type of license has a different installation CD. For customized or retail media, there is a small difference on each type of disc that will allow that installation disc to accept only one type of product key.
Only retail and volume licenses include support for end-user installation scenarios from Microsoft. OEM software is preinstalled on systems and is supported by the system manufacturer rather than Microsoft. The price of such software is lower. There are two important restrictions on OEM licenses: Microsoft does not offer technical support, and the license cannot be transferred to another computer. The cost of OEM software products bundled with systems is not disclosed by Microsoft nor by its partners, as each system manufacturer will define its own bundling price.
Microsoft recommends that system manufacturers have their systems tested, for a fee, as part of the Windows Quality Online Services (Winqual) which includes extensive testing so that no component will cause instability in the Windows operating system due to incompatibility with the Windows operating system or with other system components or their respective drivers. Having a system tested and approved will allow the manufacturer to bear the "Certified for Windows" logo sticker on the exterior of the system, and there are additional benefits for having a tested product. This includes the product's being listed on the Windows Marketplace. Because of the fees and extensive requirements, Microsoft acknowledges that smaller system manufacturers may not opt in to the program until they produce computer systems at a modest rate and on recurring designs.
 RetailRetail licenses, those purchased from a retail store in full packaging, are of two sub-types: "Upgrade" and "Full Purchase Product", often abbreviated by Microsoft as FPP. FPP licenses are transferable from one computer to another, provided the previous installation is removed from the old computer. Although upgrade licenses are also transferable, a user must have a previous version of Windows even on the new computer to which they are moving the installation. Retail licenses include installation support for end-users, provided directly by Microsoft.
 Volume LicenseA Volume License is the license given to a software version sold to businesses under a direct purchase agreement with Microsoft, and is sold as an upgrade license only, meaning that a previous license must be available for each new volume license. Volume license versions of Windows XP use a Volume License Key (VLK), which is a product key that does not require Windows Product Activation. The term "Volume License Key" refers to the ability to use one product key for multiple systems, depending on the type of agreement. Since Windows XP Volume License versions do not require product activation, this led to leaked copies of VLK media and product keys from businesses leading to piracy of Windows XP quickly spreading across the Internet upon early release. Beginning with Service Pack 1, Microsoft's active attempts to search out and blacklist known pirated VLK product keys became well known due to the inability to install the service pack on a system with one of the blacklisted keys. Later, this led to the Windows Genuine Advantage program.
 Original Equipment Manufacturer (OEM)Original equipment manufacturer (OEM) licenses are preinstalled on, and sold with, pre-assembled computers from system manufacturers. There are two types of OEM product types — those used for "direct OEMs" (major name brands that buy through a direct contract with Microsoft and produce and brand their own media from a Microsoft "Gold Master Copy" by using an authorized Microsoft duplication partner), and those used for "system builders" (local computer shops that buy generic, unbranded kits through authorized Microsoft distributors). Direct OEM product keys will often not activate with system builder installation media because direct OEMs are now required by Microsoft to pre-activate their copies in the factory using their own internal mechanism before delivery to the customer. It is recommended that system builders also pre-activate their systems before delivery, but this is not mandatory.
OEM installations can be customized using the Microsoft OEM Preinstallation Kit with branding, logos, additional applications, optional services, alternate applications for certain Windows components, Internet Explorer links, and various other customizations. All OEM customers must include support and contact information for the initial installation of Windows because it is the responsibility for the OEM to support the Windows installation, and is not provided by Microsoft to the end-user. Direct OEMs must create their own media, but have the option of creating their own custom recovery solution, which may or may not be similar to a generic installation. Direct OEMs may provide a recovery partition on the hard drive as the custom recovery solution rather than providing disc-based media with the computer.
Some end-users have found this to be a troublesome option, because in the event of an out-of-warranty hard drive failure, they may not have access to any installation media in order to reinstall Windows onto a new hard drive. System builders are not allowed the option to create a custom recovery CD/DVD media. The only deliverable media available for a system builder to give to the end-user is the unbranded OEM system builder hologram media kit. Because of this, when end-users reformat their hard drives and re-install from the installation media, they lose all the custom branding and support information that the system builder would have included.
As a supplemental recovery method to a CD/DVD-based installation, a system builder may employ a fully customized recovery solution on the hard drive. Whether utilizing a recovery partition or not, a system builder must still include the original generic OEM system builder hologram CD/DVD media kit. OEM licenses are not transferable from one computer to another. Every computer sold/resold with an OEM license must include all of the original installation media or recovery solution, documentation, Certificate of Authenticity, and product key sticker with the sale. Microsoft requires that all OEM system manufacturers include as part of the configuration the Windows Out-of-Box Experience (OOBE), which is the initial setup wizard encountered the first time Windows boots up. It is also required that value-added resellers (VAR's), retailers, and general resellers not tamper with the OEM's customized OOBE mechanism unless under permission by the OEM, and it is a recommended configuration for systems that are privately resold so that a customer will have a like-new computer experience upon first boot-up.
OEM licenses are to be installed by professional system manufacturers only. Under Microsoft's OEM License Agreement, they are not to be sold to end-users under any circumstance, and are to be preinstalled on a computer using the OEM Preinstallation Kit (OPK) before shipment to the customer, and must include at the very least the manufacturer's support contact information. They are, therefore, designed for installation only on a single computer and are not transferable, even if the original computer is no longer in use. This is not usually an issue for users who purchase new computer systems, because most pre-assembled systems ship with a preinstalled operating system. There are few circumstances where Microsoft will allow the transfer of an OEM license from one non-functioning system to another, but the OEM System Builder License Agreement (SBLA), as well as the OEM End User License Agreement (EULA) do not contain any allowance for this, so it is entirely up to Microsoft's discretion, depending on the situation