A+ Certification / Beginners

The Windows Registry

Windows configuration information is stored in a special configuration database known as the Registry. This centralized database contains environmental settings for various Windows programs. It also contains registration information that details which types of filename extensions are associated with which applications. So, when you double-click a file in Windows Explorer, the associated application runs and opens the file you double-clicked.

The Registry was introduced with Windows 95. Most OSs up until Windows 95 were configured through text files, which can be edited with almost any text editor. However, the Registry database is contained in a special binary file that can be edited only with the special Registry Editor provided with Windows.

Windows 7, Vista, and XP have what appear to be two applications that can be used to edit the Registry, REGEDIT and REGEDT32 (with no I), but in reality, REGEDT32 opens REGEDIT. They work similarly, but each has slightly different options for navigation and browsing.

The Registry is broken down into a series of separate areas called hives. The keys in each hive are divided into two basic sections-user settings and computer settings. In Windows, a number of files are created corresponding to each of the different hives. The names of most of these files do not have extensions, and their names are SYSTEM, SOFTWARE, SECURITY, SAM, and DEFAULT. One additional file whose name does have an extension is NTUSER.DAT.

The basic hives of the Registry are as follows:

    Includes information about which filename extensions map to particular applications.
    Holds all configuration information specific to a particular user, such as their Desktop settings and history information.
    Includes nearly all configuration information about the actual computer hardware and software.
    Includes information about all users who have logged on to the system. The HKEY_CURRENT_USER hive is actually a subkey of this hive.
    Provides quick access to a number of commonly needed keys that are otherwise buried deep in the HKEY_LOCAL_MACHINE structure.

Modifying a Registry Entry

If you need to modify the Registry, you can modify the values in the database or create new entries or keys. You will find the options for adding a new element to the Registry under the Edit menu. To edit an existing value, double-click the entry and modify it as needed. You need administrative-level access to modify the Registry.

Windows uses the Registry extensively to store all kinds of information. Indeed, the Registry holds most, if not all, of the configuration information for Windows. Modifying the Registry in Windows is a potentially dangerous task. Control Panel and other configuration tools are provided so you have graphical tools for modifying system settings. Directly modifying the Registry can have unforeseen-and unpleasant-results. You should modify the Registry only when told to do so by an extremely trustworthy source or if you are absolutely certain you have the knowledge to do so without causing havoc in the Registry.

Restoring the Registry

Windows stores Registry information in files on the hard drive. You can restore this information using the Last Known Good Configuration option, which restores the Registry from a backup of its last functional state. This can be used if-and only if-you have not logged in again since a change was made (otherwise, the Last Known Good Configuration option is useless).

To use this option, press F8 during startup and then select Last Known Good Configuration from the menu that appears. You can also back up the Registry files to the systemroot\repair directory by using the Windows Backup program, or you can save them to tape during a normal backup. To repair the Registry from a backup, overwrite the Registry files in systemroot\system32\config.

Automated System Recovery (ASR), which is accessible through the Backup utility, can be used as a last-resort option for system recovery in Windows XP. Both Windows Vista and Windows 7 use the WinRE recovery environment to do a Complete PC Restore to achieve the same goal.

Virtual Memory

Another thing you may need to configure is virtual memory. Virtual memory uses what's called a swap file, or paging file. A swap file is actually hard drive space into which idle pieces of programs are placed while other active parts of programs are kept in or swapped into main memory. The programs running in Windows believe that their information is still in RAM, but Windows has moved the data into near-line storage on the hard drive. When the application needs the information again, it is swapped back into RAM so that it can be used by the processor.

Random access memory (RAM) is the computer's physical memory. The more RAM you put into the machine, the more items it can remember without looking anything up. And the larger the swap file, the fewer times the machine has swapped out the contents of what it is holding in memory. The maximum possible size of your swap file depends on the amount of disk space you have available on the drive where the swap file is placed. Windows configures the minimum and maximum swap file size automatically, but if you want Windows to handle the size of the swap file dynamically, you have to change the default setting by selecting System Managed Size in the Virtual Memory dialog box. We'll show you how to get there in a moment.

In Windows, the swap file is called PAGEFILE.SYS, and it's located in the root directory of the drive on which you installed the OS files. The swap file is a hidden file, so to see the file in Windows Explorer you must have the folder options configured to show hidden files. Typically, there's no reason to view the swap file in the file system because you'll use Control Panel to configure it. However, you may want to check its size, and in that case you'd use Windows Explorer.

The moral of the story: As with most things virtual, a swap file is not nearly as good as actual RAM, but it is better than nothing!

To modify the default Virtual Memory settings, follow these steps: Click Start a Control Panel. Double-click the System icon, and select the Advanced tab in Windows XP (select Advanced System Settings from the left panel in Windows Vista and Windows 7). In the Performance area, click Settings. Next, click the Advanced tab (yes, another Advanced tab), and then, in the Virtual Memory area, click Change. Note that in addition to changing the swap file's size and how Windows handles it, you can specify the drive on which you want to place the file.

You should place the swap file on a drive with plenty of empty space. As a general rule, try to keep 20 percent of your drive space free for the overhead of various elements of the OS, like the swap file. Do not set the swap file to an extremely small size. If you make the swap file too small, the system can become unbootable, or at least unstable. In general, the swap file should be at least 1.5x the amount of RAM in the machine.
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