Windows Update: The essentials

Windows Update is a client component that connects periodically to a designated server and checks for updates. Once it determines that updates are available, it can be configured to download and install the updates automatically or to notify users and administrators that updates are available. The server component to which Windows Update connects is either the Windows Update Web site hosted by Microsoft (http://windowsupdate.microsoft.com/ ) or a designated Windows Update Services server hosted by your organization.

Unlike the automatic updating feature in previous versions of Windows, which only distributes and installs critical updates, Windows Update supports distribution and installation of the following:

• Critical updates Updates that are determined to be critical for the stability and safeguarding of a computer
• Security updates Updates that are designed to make the system more secure
• Update roll-ups Updates that include other updates
• Service packs Comprehensive updates to the operating system and its components, which typically include critical updates, security updates, and update roll-ups
• Optional updates Updates that may be useful, including updates for drivers.

A key part of the extended functionality allows Windows Update to prioritize downloads so that updates can be applied in order of criticality. This allows the most critical updates to be downloaded and installed before less critical updates. You can also control how a computer checks for new updates and how it installs them. The default polling interval used to check for new updates is 22 hours. Through Group Policy, you can change this interval. By default, every day at 3:00 A.M. local time, computers install updates they've downloaded. You can modify the installation to require notification or change the install times.

Windows 7 reduces the number of restarts required after updates by allowing a new version of an updated file to be installed even if the old file is currently being used by an application or system component. To do this, Windows 7 marks the in-use file for update and then automatically replaces the file the next time the application is started. With some applications and components, Windows 7 can save the application's data, close the application, update the file, and then restart the application. As a result, the update process has less impact on users.

Automatic updating uses the Background Intelligent Transfer Service (BITS) to transfer files. BITS is a service that performs background transfers of files and allows interrupted transfers to be restarted. BITS version 3.5, which is included with Windows 7, improves the transfer mechanism so that bandwidth is used more efficiently, which in turn means less data is transferred and the transfer is faster. Through Group policy, BITS can be configured to download updates only during specific times and to limit the amount of bandwidth used. You configure these and other settings by using the Set Up a Work Schedule To Limit The Maximum Network Bandwidth Used For BITS Background Transfers policy. This policy is found in the administrative Templates policies for Computer Configuration under Network\ Background Intelligent Transfer Service (BITS) In Group policy. additionally, by using BITS 3.5, Windows 7 can obtain updates from trusted peers across a local area network (LaN) as well as from an update server or from Microsoft directly. Once a peer has a copy of an update, other computers on the local network can automatically detect this and download the update directly from the peer, meaning a required update may need to be transferred across the wide area network (WaN) only once rather than dozens or hundreds of times.

You can use automatic updating in several different ways. You can configure systems by using the following options:

• Install Updates automatically With this option, the operating system retrieves all updates at a configurable interval (22 hours by default) and then installs the updates at a scheduled time, which by default is every day at 3:00 A.M. This configuration represents a change in behavior from Windows XP because users are not required to accept updates before they are installed. Updates are instead downloaded automatically and then installed according to a specific schedule, which can be once a day at a particular time or once a week on a particular day and time.
• Download Updates But Let Me Choose Whether to Install them With this option (the default), the operating system retrieves all updates as they become available and then prompts the user when the updates are ready to be installed. The user can then accept or reject each update. Accepted updates are installed. Rejected updates are not installed, but they remain on the system so that they can be installed later.
• Check For Updates But Let Me Choose Whether to Download and Install them With this option, the operating system notifies the user before retrieving any updates. If the user elects to download the updates, she still has the opportunity to accept or reject them. Accepted updates are installed. Rejected updates are not installed, but they remain on the system so that they can be installed later.
• Never Check For Updates When automatic updates are disabled, users are not notified about updates. Users can, however, download updates manually from the Windows Update Web site.

When Windows Update is configured for automatic download and installation, users are minimally notified of update availability or installation. Clicking a notification on the taskbar allows you to get more information about an update.