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List of common system file extensions

You can encounter these files in various operating systems. You should not try to alter or delete any of these files unless you know what you are doing.

Common system file types may change in time as the popularity and significance of some formats can change.
Whole category of system file types contains now 478 file types. Show all system file types.


An alx file extension is used for files that contain data used for installation of apps to BlackBerry smartphones. ALX is text format viewable in every text editor.

blf file icon blf 

Files with blf file extension are commonly found as temporary files generated by latest Windows operating system to prevent registry corruption whenever a change to registry is done.

cpl file icon cpl 

A cpl file extension is related to the Microsoft Windows operating system. A cpl file stores settings of Windows Control Panel applets.


A dat file extension is traditionally associated with variety applications and is used to identify files that contain application data resources.

dll file icon dll 

Files with dll suffix can be commonly found as dynamic link libraries for Microsoft Windows system and apps. These files act as modules with additional runtime routines or data.

drv file icon drv 

Files with drv extension are commonly found as device drives, especially in older versions of Windows operating system. Used for system purposes.


Files with dump extension can be usually found as various dump files generated by programs when some error is encountered in the system. Used for analysis of the errors to help troubleshoot it.

evtx file icon evtx 

Files with evtx suffix can be usually found as event logs generated in Microsoft Windows operating system. An event log file contains various information how programs are working, and type of errors they encounter.

gadget file icon gadget 

A gadget file extension is used for Windows Gadgets, small programs that enhance the desktop with various features. Gadgets are usually located in the Windows Sidebar, on the right side of desktop.


Files with idx suffix can be usually encountered as various index files from all kind of programs and applications.

inf file icon inf 

Files with inf extensions can be generally found as various installation scripts in Microsoft Windows operating system.

kext file icon kext 

Files with kext extension can be commonly found as system files in Mac OS X (macOS) operating system. Kernel files.

key file icon key 

Files with key extension can also be found as registry entries for o Microsoft Windows operating system.

mui file icon mui 

Files with mui extension are mainly related to Microsoft Windows are used for language packages with which you can add the default localization of your OS.

ocx file icon ocx 

An ocx file extension is associated with the Microsoft ActiveX Control items. An OCX is an OLE custom control (program) that is used by various Windows applications to provide such function as handling scroll bar movement and window resizing.

reg file icon reg 

Files with reg extension can be usually found as Windows registry files, special files that contain exported registry entries that can be uploaded to the system.


A rom file extension is frequently used for various ROM images for BIOS or hardware firmware updates. Can also be a Read Only Memory image from older computer types used in various emulators.

scr file icon scr 

The scr file extension is associated with screensavers created for Microsoft Windows operating system.

sfcache file icon sfcache 

The sfcache file extension is used for Microsoft Windows ReadyBoost cache files. SFCACHE file is stored on flash memory device (USB flash, SD card, CompactFlash etc.) and is used to faster random disk reads that speed up a computer. ReadyBoost is available in Microsoft Windows Vista and Microsoft Windows 7.


Files with swp extension can be commonly found as various swap files generated by operating systems or programs for memory paging purposes.


Files with sys extension can be often found as various system files in DOS and Windows operating system. They contain information needed to properly load and configure operating system. A corrupted or missing system file can cause the system to be unstable or unable to boot.

vxd file icon vxd 

Files with vxd extension can be mostly found as virtual device drivers from Microsoft Windows operating system.

This is a list of some the most common file types from this category and may change in time as the popularity and significance of some formats can change. Whole category of system file types contains now 478 file types. Show all system files.

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