In-depth understanding of disk fragmentation

If you are using Windows XP, pay attention to disk fragmentation.

1. Why fragment?

The file layout on the disk will strongly affect the I/O performance. files and directories that are severely fragmented or scattered on the disk will damage the performance, although Windows XP will automatically relocate some files to improve performance, this is not a common requirement of the system, and usually only contains a small part of files on the disk.

In this regard, the complete disk fragmentation should be performed immediately after the system installation is complete. By default, WindowsXP performs Partial Fragment once every three days, and adjusts the physical location of the file on the disk according to the usage of the day. The moved file is written to Layout. INI file. This is the physical location of the file on the disk that Windows XP considers to be arranged in this order. The file path is in C: WindowsPrefetch.

The system automatically sorts out disk fragments when idle, and reads Layout first. the content in the INI file, and partial fragment of the files involved in it, which is also the basis for the disk sorting program to transfer the file location.

2. gain an in-depth understanding of the Prefetch directory

In Windows XP and later operating systems, the pre-read function (also known as "pre-load") is added, which can improve the system performance, speed up system startup and file reading. These pre-read files are saved in the % systemroot % Prefetch directory, *. pf is the extension *. the pf file contains the detailed information about the file to be loaded and the loading sequence.

Each application, including the Windows XP startup process, will leave the corresponding pre-read files in the PrefetCh directory. The pre-read files describe the loading sequence of each module during the application or startup, the naming method is based on the name of the executable file of the application, plus a hexadecimal value that describes the complete path of the executable file, plus the file extension. pf, e.g. QQ.EX-0065A2A1. pf. Every time you start a program, a record is automatically left in the *. pf file corresponding to the Prefetch directory. However, the preread file started by Windows XP is always the same name, that is, the NTOSBOOT-B00DFAAD.PF, which contains records of the file loaded at startup.

When a system is started or a program is running, Windows loads all the files recorded in the *. pf file into the memory instead of loading files one by one based on commands. In addition, Windows will use the *. pf file of the startup program or program to develop an optimal disk allocation scheme. Information about this scheme is stored in the Lyaout. ini file.

3. Do not allow the system to automatically clear disk fragments

Sometimes, you may feel that the local fragment function is very boring, because the disk fragment will also perform some operations on the hard disk. It seems rational that some tips are circulating on the Internet to disable local fragment by modifying the registry key value, but in fact these so-called tricks are completely ineffective. In fact, even if you delete all the files in the C: WindowsPrefetch directory, the system will still automatically create Layout after you restart the system. INI files, the automatic part sorting function will be re-activated once every three days. The correct method is to use NotePad to open Layout. INI file, delete all the content in it, and set this file as a read-only attribute, so Windows XP cannot activate the automatic Partial Fragment function. Of course, you don't have to worry about C: windowsPrefetch will become larger and larger.

4. Further Discussion

We often see online tips on how to modify the registry key value to increase the startup speed of Windows XP. Are these skills really effective? Next, we will take an in-depth discussion based on the disk fragment instance:

Question 1: Why cannot I fragment disk C?

Windows XP system, in the C disk fragment, the prompt is caused by C: WindowsprefetchWMIPRVSE. EXE-28F301A9.PF File Corruption, the scan cannot continue.

C: WindowsPrefetch is a pre-read folder of Windows XP. Windows XP stores frequently-used data in the pre-read folder, which can greatly speed up reading when the data needs to be used again, but as time goes on, the head of this folder will become larger and larger, and there may be some dead chain files. At this time, if you perform fragment, the above error may occur, the solution is to clear the folder and sort the fragments.

Question 2: Can fragments be sorted at startup?

Windows XP can fragment during startup so that files necessary for startup can be arranged adjacent to each other to increase the speed at next startup, however, this function is disabled by default. The activation method is to open the Registry Editor, find HKEY_LOCAL_MAHCINESOFTWAREDfrgBootOptimizeFunetion, double-click the Enable key in the right pane, and change the key value from the default "N" to "Y.

Question 3: Can pre-read prohibition improve the system startup speed?

There is a tip on improving the startup speed of Windsws XP on the network. Specifically, you can modify the EnablePrefeteher sub-key in the HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlSession ManagerMemory ManagementPrefetchParameters directory in the registry, assign the key value "1 ". This reduces the number of pre-read files and the wait time of the progress bar. The result is that the log-on screen is displayed when the progress bar is circled.

Microsoft's technical documentation explains the meaning given to different values by EnablePrefetcher:

0: the pre-read function is canceled;

1: Only pre-read applications;

2: Only pre-read Windows files.

3: Pre-read Windows system files and applications. This is the default value of Windows XP.

Although the EnablePrefetcher key value is set to 1, it can indeed reduce the number of pre-read files, but the system initialization of the kernel is a very complex process, at this time, we need to load many underlying drivers, startup subsystems, and related services. Even when we see the welcome screen, we cannot think that the system has been started, because the system will continue to initialize the loading of those unfinished drivers in the background, although the number of scroll bar actions is greatly reduced, the black screen process before the welcome screen is displayed has increased, therefore, the overall system time has not changed.