A computer file is a collection of data that has a name (called the filename). When we want a computer to remember data​, say some text, formulas, images​ for later​ use ​, we store it in a file ​.​A filename is just the name that a user or program titles the file To make it easier to sort through our files​.​Almost all the information on a computer is stored in some type of file.  data file (contains data such as a group of records); executable file (contains a program or commands that are executable); text file (contains data that can be read using a standard text editor). 

The name itself doesn’t affect the contents of the file, so even if a video file is named something like image.mp4, it doesn’t mean it’s suddenly a picture file.​It is the extension that matters.​The computer keeps track of additional details, like when the file was last updated, the type of file, and who’s allowed to edit it. That’s called metadata: the data about the data.
Files in any operating system are stored on hard drives, optical drives, and other storage devices. The specific way a file is stored and organized is referred to as a file system​

The first attempt of any anti-virus product is to repair the damaged files or sectors of the disk. However, if the anti-virus does not know the method of repairing the infection then it isolates the infected file to quarantine for a possible repairing in future. If a virus is found to be too dangerous or the file is severely damaged then the antivirus may decide to delete the infected file.

Thus the actions are generally configured in a sequential order, such as, repairing the file (most preferred), quarantining the file (if cannot be repaired) and deleting the file (least preferred).

The anti-virus ​uses various methods to remove the virus and repair the file to bring it back to its original form​​. This Removes the infection from the file but does not actually delete the file itself. This is the best option if you need to keep the file.​

Quarantine computer file

Sometimes the anti-virus knows that the file is infected but does not know how to disinfect it (nor has a copy in backup). In such cases, the anti-virus puts the file into the quarantine​,​ ​meaning it isolates it ​in order to prevent it from contaminating other parts of your computer. ​An infected file in quarantine, it deletes the file from its original location and makes changes to it so that it cannot run as a program.

This is the worst out of all the options that an anti-virus may resort to. When a file is totally damaged or infected by dangerous viruses then the anti-virus decides to delete it. Deleting a file may result in non-functioning of an application or Operating System.

Quarantined files cannot harm your computer but they do still take up valuable space on your hard drive.​In case an antivirus can not repair it, it is best to delete it from the computer.