Windows XP Prefetch and how it is used

Windows Prefetch files are basically log files created by the windows operating system. They contain information on the files accessed during Windows boot-up and 1 minute after boot-up to account for other applications loading up in the background. These log files also contain in which order these files are loaded during boot-up. By setting the configuration for the log files, you can have windows log the applications and files the user accesses while in windows as well. It does the logging intelligently, only adding the files if windows believes those files will be accessed relatively frequently.

If you enable this option, windows will create a (.pf) prefetch file for each program that has been logged in windows. Each (.pf) prefetch file contains information on the behavior (information primarily on the order in which files are accessed by the program) of one application; the application that it is named after. Of course this will not happen, unless you set the configuration settings in the registry. The reason for this is because by default windows just keeps track of files accessed during boot-up and 1 minute after boot-up has completed.

This is the registry path to change the prefetch parameters:ROOT\HKEY_LOCAL_MACHINE\system\ControlSet001\Control\Session Manager\Memory Management\PrefetchParameters. Inside of this section is a list of parameters. The the most important parameter is the 'EnablePrefetcher' parameter. Set the Value to '3'.

windows is constantly monitoring the files and applications that it is configured to('EnablePrefetcer' parameter), by updating the individual program lOG files (.pf).

There is a log file that is updated about once a month. The file is named layout.ini, and contains all the files that are to be put at the beginning of the drive. This is the file that PerfectDisk uses to get the list of BOOT files. The built-in windows defragmenter supposedly takes advantage of the layout.ini file, but I have not found any improvement in performance when I have run the built-in defragmenter, not to mention the fact that it does not defragment nearly all the files on my hard drive. But that is beside the point. We are talking about Prefetch files, not a crappy built-in defragmenter!

The Prefetch logging has proven time and time again to drastically decrease boot-up time and application launch time, because all of the files that the user needs is at the beginning of the drive, unless of course the user opens an application/file that has not been opened many times or at all before and has not been added to the Prefetch list.

The reason for decreased boot-time when the boot-up files are at the beginning of the disk is this. The beginning of a hard drive is at the outer tracks of the disk platter. These outer tracks provide quicker access because the data cylinders (sectors) are flying past at a quicker rate (more surface area per revolution), and therefore quicker data extraction. In addition to putting these files at the beginning of the disk (or partition depending on situation), these files are placed one after another, providing extremely good performance escpecially upon boot-up because of this.

The servo on a hard drive move the read/write heads over the desired track for data reading/writing. Now, there is only one servo in a hard drive, and if the data that the hard drive is requested to access is spread about on tracks on different sides on the platter, it takes time for the servo to move to the correct track before reading/writing data. But, if all the data that is requested in a given amount of time is all at the beginning of the platter(s), then the servo will not have to move very far to access data, causing extreme performance. By the way, one of the main reasons that hard drives are so slow is because of servo delays (slowness), after all fragmented drives prove it so easily.