Is this the function of a file format?


I have trouble understanding file formats, or maybe I have figured it out. Please help me!

A file format is a specification that tells how the data of a file is arranged and thus how it is to be interpreted. Does this mean, for instance, that data arranged according to a JPEG (an image format and codec) will tell my computer that the data is to be interpreted as an image?

In: 16

Yes. The format of the file is how the bits are arranged in a file. However, there is more (generally) to a file than the arrangement of the bits. There is most often a collection of special bits at the very beginning of a file that help the computer or program to determine what type of file it is, these are called “magic bytes”. Using the JPEG format for example, the “magic bytes” at the very beginning of the file (in hexadecimal) are “FF D8 FF EE”. When the computer reads this file it sees these bytes and says “Aha! This is a JPEG format file!” and then it knows how to follow the pattern to “read” that file format and can then display it.

Basically, yes! The file type extension (.jpg .gif .whatever) tells the computer operating system (OS) what processes to use when opening the file. They read (expect to find) a header section of the file containing things like the date, size, x and y pixel size, as well as other info like geocaching. Then the OS knows how to display the file through whatever app is in use.

Edit: thanks u/ISwearImNotAnAI
Not sure how I ended up misinterpreting OP’s question, but anyway, others have already explained how this works. I’ll leave it up but just know what’s below is NOT a “direct” answer to OP’s question.

That’s correct. Operating systems (computers, more broadly) specifically know how to interpret/present files with specific file extensions. These are used by the computer to decide what program to open the data in. For example, JPG opens in preview on Mac.

Commonly used file extensions, such as JPG, PDF, and PNG, have agreed-upon file structure (how the data is formatted), which is why any operating system (MacOS, Windows, Linux, etc) is able to open/edit/save them.

Some file extensions are “proprietary”, or belong to specific software and/or operating systems. Two examples off the top of my head are HEIC (iPhone photos) and more commonly seen Docx/xlsx/pptx (Microsoft word/excel/PowerPoint).
HEIC is (or at least was before) only used in the Apple ecosystem. Docx/xlsx/pptx are all only (supposed) to be opened using Microsoft Word/Excel/PowerPoint, although I know these documents can also be opened in Google Docs/Sheets/Presentations (I forget Google’s PowerPoint equivalent).

You can also make your own file extension! Very uncommon, for sure, but it is possible. The issue with creating your own is that you have to tell your computer how to interpret it; and, any other computer that the information is sent to won’t know what to do with that file either.
I have only seen custom file extensions used for saving game data. For instance, the videogame “Timberborn” uses the .timberborn file extension for save-game data. The game will know what to do with the data, but your computer will not if you tried to open those files yourself.

Let me know if you have any other questions or further explanation, I hope this helped!

TLDR; you are right, file extensions tell the computer how a file’s data is structured and how to open/interpret the data.

Think of it if the file is like a screw or bolt. The file format is like the top of the bolt that tells you what bit to use – Phillips, flat head, star, hex, etc. You can’t turn the bolt unless you know what type it is.

The computer can’t open the file unless it knows what type of file it is.

Yes. But the rabbit hole goes a bit deeper. You can theoretically have the exact same image in PNG and JPEG file formats. In both cases you tell the computer that the file is to be interpreted as an image, but the data is arranged in wildly different manners.