A Crash Course in Device Drivers
Before Windows can work with any piece of hardware, it requires a compatible, properly configured device driver. Drivers are compact control programs that hook directly into Windows and handle the essential tasks of communicating your instructions to a hardware device and then relaying data back to you. After you set up a hardware device, its driver loads automatically and runs as part of the operating operating system, without requiring any further intervention on your part.
Windows includes a library of drivers for internal components such as sound cards, storage controllers, and display adapters as well as external add-ons such as printers, keyboards, scanners, mice and other pointing devices, digital cameras, and removable storage devices.
This core library is copied during Windows 7 setup to a protected operating system folder, %SystemRoot%\System32\DriverStore. (Driver files and associated elements are stored in the FileRepository subfolder.) Anyone who logs on to the computer can read and execute files from this location. But only an installation program working with authorization from a member of the Administrators group can create or modify files and folders there.
You can add new drivers to the driver store in a variety of ways. Windows 7 Update offers drivers when it detects that you’re running a device that is compatible with that driver and is currently using an older version. (You can also search for the most recent driver viaWindows Update when installing a new device.) In addition, installing a Windows 7 service pack typically refreshes the driver store with new and updated drivers. All drivers that are copied here from Microsoft servers are certified to be fully compatible with Windows and are digitally signed by Microsoft.
As an administrator, you can add third-party drivers, signed or unsigned, to the driver store by specifically giving consent. All drivers added to the driver store in this fashion are saved in their own subfolder beneath the FileRepository folder, along with some supporting files created by Windows 7 , allowing them to be reinstalled if necessary. Any driver that has been added to the store, signed or unsigned, is considered to be trusted and can be installed without prompts or administrator credentials.
In Windows 7, you do not have to be an administrator to install drivers; Windows 7 checks the current driver installation policy to determine whether installation is permitted. When you install a new Plug and Play – compatible device, Windows checks the driver store first. If it finds a suitable driver, installation proceeds automatically. If no compatible driver is available, you’re prompted to search for driver software.
By default, Windows 7 installs drivers from trusted publishers without prompts and never installs drivers from publishers that the user has chosen not to trust. When you attempt to install a signed third-party driver and have not previously designated the publisher as trusted or untrusted, you’re presented with a consent dialog box. In addition to confirming the installation of the driver in question, this Windows Security dialog box gives you the opportunity to confer trust upon the driver’s publisher. If you agree to trust the publisher, subsequent driver installations from that publisher will proceed without your explicit consent.
To be properly installed in Windows 7, a hardware driver must have a Setup Information file (with the extension .inf). This is a text file that contains detailed information about the device to be installed, including the names of its driver files, the locations where they are to be installed, any required registry settings, and version information.
All devices with drivers in the DriverStore folder include Setup Information files in the %SystemRoot%\Inf folder. The basic structure of a Setup Information file is similar to an old-fashioned Windows 3.x–style .ini file. Each piece of setup information appears on its own line under a bracketed section heading. Windows will not allow the driver package to be copied into the driver store unless these sections are present and filled in correctly.
In particular, an .inf file must contain valid [SourceDisksFiles] and [SourceDisksNames] sections. At the time the .inf file is copied into the driver store, Windows creates a folder for the driver files using the name of the .inf file with an eight-character hash appended to it.
Inside that folder, Windows uses the data in the .inf file to create a Precompiled Setup Information file with the .pnf extension, which it uses for installation tasks. Although the Setup Information file is a crucial part of the driver installation process, you don’t work with it directly. Instead, this file supplies instructions that the operating operating system uses during Plug and Play detection, or when you use the Add Hardware wizard or a setup program to install a device.
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