This is written to give a basic, essential understanding of one of the major things needed to be able to control your own system and files, files which you have created and you need to manage for years to come.
Every windows file has a name you give it so you know what file it is, you already know that, and you know you can rightclick and 'rename' any file.
After the name of a file, you see the period ( . ) and then 3 letters like .DOC or .JPG and so on. That part of a filename is called the 'extension'.
So far so good, yes?
Now, whatever text is to the left of the period is so you know what the file is, and whatever is to the right of the period is so the computer knows what TYPE of file it is.
When a computer knows what TYPE of file it is, it then knows what PROGRAM to open that file with. The EXTENSION is on the end of every file so the computer knows what kind of file it is. If it ends in .JPG and you open the file, the computer says "oh, that is a photo, I will open it with my photo program", if it ends in .DOC and you open it, the computer says "ah, this is a word document, I must open this file in Microsoft Word", and if the file ends with .HTM and you open it, the computer says "this file is a webpage, and I'll open it in Internet Explorer".
Without an extension, your computer does not know what type of file it is, and therefore will not know what program to open it in. Try renaming any file you have and delete the extension (you can add it back after this experiment by renaming it), now try opening the file, and the computer will not open it but will ask you "what program am I supposed to open this file with?". Add the extension back and try opening it again, and the computer will open it as normal because it knows again.
With the wrong extension, your computer may give you an error. Try renaming a photo of yours by changing the .JPG extension to a .DOC or anything else, and then try opening it. The computer will see the .DOC and say "oh this is a text document so I will open it in Microsoft Word" and then when microsoft word opens, you'll see a bunch of gibberish text. That's because the 'data' in the file is actually a photo, but because you tricked the computer into thinking it was a text document, it tried to open it as text, and that doesn't work. Now rename the file back to the normal .JPG and re-open the file. Now the computer goes back to opening it on the assumption it is a photo again.
You can't lose information in a file by accidently removing the extension, or by giving it the wrong extension, you will just get an error like "I don't know what type of file this is and what to open it in", until you give it the right extension again. Then all is well.
This is why it is very important to know some of the more common extensions you see weekly on your system, or that people email you files, or you download files; they all have extensions.
Some programs can open more than one type of extension, like Microsoft Word can open .DOC and .TXT and even .HTM. Though a program may be able to open different types of extensions, usually one program is better than other programs at working with certain files. Like you can open an .HTM file (a webpage) in Microsoft Word and you can see it, but Internet Explorer is better to view webpages as you know.
Because you can have different programs on your computer which can open the same type of extension (say .JPG for instance), in a computers 'control panel' there is a section to assign what program opens what extension when you open that file. Many programs will open a .JPG file, but if you want photoshop to open .JPG files, you have to go to the control panel and assign .JPG to photoshop, that way when you open the file it will open in photoshop and not another program you don't want it to open.
One problem with installing new programs is that the new program will change your settings, and it can (without telling you) change system settings so that when you go to open a file, it opens in the new program, and you may not want that. That's when you have to go and change it back so the extension opens in the program you wanted it to. For instance, if you click on a .MP3 file and you know winamp will open, and then you install apples quicktime program, afterwards when you click on a .MP3 it may open up in quicktime instead of winamp, because quicktime went and told your computer "when they click on a .MP3 file open it in quicktime and not in winamp". Media player programs do this alot with .MP3 and .AVI and .MPG and others, so you have to know how to control your system, to control what program opens what extensions.
This list below is a list of common file formats (aka extensions), and again, it is good to know what extensions are because they'll be around a long, long time and most people unfortunately have no idea what they even mean.
Some extensions on a computer aren't meant for regular users to mess with, because the operating system needs those certain files to perform certain tasks, and programs you install also place files on your hard drive, each with an extension, and those you shouldn't mess with either. For instance, here's some file extensions not to mess with- .DLL .INI .DRV .LOG .SYS .INF .OCX .XML .REG and some others. I don't list those below because you just shouldn't touch those unless you know what they are there fore, again, those are files that 'programs' are composed of. The computer knows those extensions arent photos or movies or songs or texts or webapges, the computer knows those are actual programs instead.
There are 1000s of extensions and every one has a meaning, again I am only listing the most common ones you'll see in daily life, go HERE to see a big list of them in case someone ever sends you a file with an extensions you aren't familiar with.
If you don't have the program needed to open an extension, then when you try to open the file the computer will ask "what program should I try to open this file with?". For instance, people often email other people .PPS files, and those are Microsoft Powerpoint files, and many people don't have that program, so they can't open it at all until they install Microsoft Powerpoint.
Lastly, some extensions are the same 'type' of file, but differ to certain ways, for instance -
AUDIO FILES
.WAV is a perfect copy of a sound, but .MP3 is not a perfect copy of sound. The reason .MP3 is so popular though is because a .MP3 file is about 10-20 times smaller in filesize than a perfect .WAV file. The reason it is smaller is because a .MP3 is not a perfect copy; lots of the original sound has been 'thrown away' so it fits in a smaller space on your hard drive. The people who developed the .MP3 format tried their best though to make sure the 'thrown away' information is sound that the average person couldn't hear anyways (but a good stereo you will be able to hear the difference between the same song as a .WAV file compared to a .MP3 file, that's why sometimes .MP3 files sound 'whistly' or 'chirpy')
VIDEO FILES
.AVI can be a perfect copy of a video, but .MPG is not a perfect copy of video. The reason .MPG is so popular, again, is because the file size is much much smaller than a .AVI file of the same exact video. And again, the reason it is smaller is because the .MPG throws away lots of the original video data so it fits in a smaller space. The people who developed the .MPG format/extension though made it so you could barely notice the missing information (but you'd be able to tell the difference if you saw a perfect .AVI video file as compared to a .MPG file of the same video, because .MPG videos can sometimes look 'blocky' or 'smeary' especially when you make the video size onscreen bigger.)
PHOTO FILES
.TIF is a perfect copy of a photo, but a .JPG is not a perfect copy; lots of information in the photo has been thrown away, and again it makes the size much smaller, and again the people who 'developed' the .JPG format/extension tried to make it so that you would barely be able to know what information in the photo was thrown away. If you saw a .TIF and a .JPG of the same photo, you would be able to tell the difference, especially when zooming in on the photo, you would notice the .JPG has 'blockiness' and reduced color fidelity. That's why if you have a digital camera, and if there is a setting to choose to save your photos as .TIF or .JPG, you will have much nicer photos saving them as .TIF
ETC
So I hope you get the point; you can have extensions that are the same 'type' of file, but often one is a better choice than another if you want a better quality. Plus, you can always 'convert' files from one type to another if you needed to, like to share them with others via email and so forth. For instance -
- if you wanted to save a perfect original sound, you would save as .WAV, and then if you wanted to share it with someone as a smaller .MP3, you would make a copy of the .WAV and convert it to a smaller .MP3, and then you'd have two versions; one large and original, the other smaller and reduced quality.
- if you wanted to save a perfect original video, you would save as a .AVI, and then if you wanted to make it smaller to email someone or such, you could make a copy of the file and convert it to .MPG, and you would have two versions of the same video - a high quality original, and a smaller lesser quality version.
- if you want to save a perfect original photo, you would save it as a .TIF, and then if you needed it as a .JPG again you would just make a copy and convert it to .JPG so it was smaller (through throwing details away).
This is why there are programs that 'convert' files from one type (or extension) to another, because sometimes you can have different needs for the same exact file. But to keep high-quality files and then only 'down convert' to lesser qualities when needed, if your best choice. Especially for photos. If you are paying someone to take photos for you, for instance, ALWAYS insist they give you the .TIF copies and not just the .JPG ones with so much information (such as sharpness, color, etc) thrown away. You can always 'down convert' those .TIFs later and still save the high quality originals. Professionals that just offer .JPGs to you aren't professionals at all and are a disgrace.
So now that that's all out of the way, here is a listing I made to quickly explain file types/extensions/formats you might see, and what the most common program is that will open that extension (although again another program might've changed your settings, or you might want to change setting so another program of your choice opens it). If you need details on any certain extension, just ask me:
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