CTL files are short for CONTROL files and they correspond to binary files from a particular system or application.  In most cases, CONTROL files have .CTL extensions and they typically contain important information like database details or user control information.

In the case of the Oracle Database system, CTL files are very important files in the sense that they contain details on the way the database is physically structured.  Contents of Oracle CTL files include the name of the database itself, names of other databases that are related and connected to the main database, locations and log information of these database files including the log sequence number.  CTL files under the Oracle system also contain important checkpoint information.  With all these information stored on CTL files, they also perform important functions.  Without them, the Oracle database cannot be opened or edited and data recovery will also prove to be difficult.

In the case of other applications and systems like Active X under the Visual Studio suite of Microsoft, Control files also perform very important tasks.  When programming using Visual Basic, all source codes are stored under the CTL files.  Whenever a programmer needs information about user control in Visual Basic for example, he/she only needs to check on the CTL or Control files. These files can easily be opened through a standard text editor. For any code editing, one just needs to make the changes directly on the text editor in order to effect the changes on the CTL file.

For people who encounter CTL files in their computers, it is best that they do not remove it from their computers.  When trying to open these types of file, it is also suggested to let the computer search the appropriate program to open the file.  Otherwise, one may try to select other options to gain access to the file.  In cases where the file reveals the source codes for a particular application, users should also practice caution when it comes to editing or handling syntax as it will affect the entire program itself.