Windows 7 some of these folders contain files for specific functions. For example, the ehome folder includes Windows Media Center files and the Fonts folder stores Windows fonts.
A few of these folders contain core operating system files, and it’s worth focusing on these folders, because this is where file corruptions are most likely to occur.
X:\Windows\Boot. This folder contains files necessary for starting Windows 7.
X:\Windows\Help. The Windows 7 help files are located in the Help folder. If you cannot start Help, these files might be corrupt or missing.
X:\Windows\inf. Windows uses the INF files in this folder when installing hardware and software drivers.
X:\Windows\System32. This folder contains the guts of Windows 7. All the main Windows components are located here. If you have a problem with a Windows file, it is likely located in this folder.
The following files are commonly located within the X:\Windows\System32 folder sub-structure.
ActiveX Files (*.ocx) ActiveX is a programming framework that software authors use to design reusable components to be shared across applications. Sometimes these controls are shared across programs from different software houses, and in older software, there might be incompatibilities with various versions of the .ocx files. For example, one program might require a specific version of the file, but another program needs a different version. Windows 7 is much better at handling these conflicts than previous versions of Windows; however, such conflicts can still occur.
Applications Applications are the main programs that comprise Windows 7. If you are trying to launch a built-in Windows feature and it cannot be found, the associated application file might be missing from the Applications folder.
Application Extensions (*.dll) Dynamic Link Library (.dll) files are shared library files. Like .ocx files, .dll files are program and Windows components that can be shared across software applications. Occasionally, Windows becomes unresponsive because a .dll file is corrupt or is an incorrect version that is not supported by the program or feature trying to access it.
As with .ocx files, Windows 7 is much better than previous versions of Windows at handling .dll file conflicts, but issues with these files can still occur. Windows 7 includes more .dll files than any other type of file.
Control Panel Item (*.cpl) Windows 7 launches .cpl files when you access features in Control Panel. If an item cannot be found, the associated .cpl file might be missing or corrupt.
Device Driver (*.drv). The Device Driver folder contains certain Windows 7 software and hardware drivers. These files can occasionally become corrupt.
Boot. The Boot folder contains the programs required to start Windows. If these files are deleted or become corrupt, Windows will not start.
Drivers and DriverStore. These folders contain all of the software drivers for your hardware. You can back up these folders and restore them manually if an event such as a driver malfunction or faulty driver upgrade causes problems with Windows 7.
Microsoft Common Console Document. The Microsoft Management Console (MMC) programs are stored in this folder. If you cannot start an MMC item, the program file might be corrupt or missing from this folder.
VBScript Script File (*.vbs). Visual Basic VBScript scripts can be a target for virus writers. Some VBScript scripts are stored in the main Windows 7 folders.
X:\Windows\winsxs Earlier, I discussed side-by-side compatibility protection for different versions of .dll, .ocx, and other files in Windows 7. Windows stores and organizes compatible duplicate versions of files in the winsxs folder. This folder is usually very large and even bigger than the System32 folder.
X:\Users\AppData. In each user’s folder is a subfolder named AppData. Application-specific files and settings are stored in this folder.
The AppData folder is hidden by default, so you will need to change the default setting to show hidden files to see the folder contents.
Windows 7 Security and Policy Folders
Windows security and other policies that control login, software, and user behavior and permissions are stored in the following folders.
The Windows 7 Registry
The registry is a database that contains configuration options and settings for Windows and your installed programs. There is one registry folder named NTUSER.DAT for each user. You can see one hidden registry file and can make all of them visible by showing hidden and operating system files.
The main folders containing wallpapers and other personalization options are:
Windows 7 Logs
Several folders contain Windows 7 logs. You can normally access these logs through Control Panel and Microsoft Management Console. You can also access the logs manually if you can’t get Windows 7 to start. You can find the logs in the following folders.
Temporary Files Stores
You can delete all the contents in several Windows 7 folders if you suspect they are causing problems.
• X:\Windows\Downloaded Program Files. Windows does not usually use this folder, so it will normally be empty anyway.
• X:\Windows\Prefetch. Windows tracks what programs and files you frequently use and stores this information in the Prefetch folder to preload them when appropriate (for instance, when starting a program you run often). Sometimes the prefetch files can become corrupt. If you suspect this has happened, you can safely delete the contents of this folder. Windows will then rebuild the prefetch database.
• X:\Windows\SoftwareDistribution. This folder contains Windows Update configuration options and downloaded files. If Windows Update will not install updates, you can delete the contents of this folder to try to fix the problem.
• X:\Windows\Temp. This folder is the temporary files store. Its contents can be deleted at any time if you suspect one or more temporary files is causing a problem.
Source of Information : Microsoft Press - Troubleshooting Windows 7 Inside Out