What does compressing a file mean?

Question

Can you make files smaller then extract them?

I'm new to this so I have no idea about anything.

Answer 1

Compressing a file means exactly that: they are made smaller, so they take up less space on a disk or when sending/receiving them.



Some types of files, such as text, can be compressed much more than others, such as image or video files.



"Zip" is a very common compressed file format.

Answer 2

California Bear is right on. To put another way, assume you have data file. It's filled with a combination of 1's or 0's. Ex. 1111111111000001111111111 (10 one's, 5 zeros, 10 ones). Instead of saving the 'raw' data, it records information about the file.. like (& I'm making this particularly simple algorithm up..) 0xA5A0 (A = hexadecimal value for 10, so you have "10,5,10,0" to represent the alternating number of ones & zeros ). This translates into a series of 1's & 0's ("bits") that looks like 1010 0101 1010 0000. The result is 16 bits long instead of the original 25 bits long.

This type of compression is called a 'loss-less' compression because the original data can be restored without losing any of the original content.

The alternative is called a 'lossy' compression, where some of the data is lost & can't be recovered. The MP3 music format is an example 'lossy' compression. Since human ears are only susceptible to a small range of audible sounds,

the compression throws away the information that we can't hear anyway. This is why some audiophiles are bigotted against MP3. MPEG & JPEG are loss-less methods and use a scheme similar to what I described above.

Answer 3

There are various methods used in compressing a file but they all operate on the same basic principle. A program looks at the file and uses a math formula (algorithm) to substitute a value in place of the data in the file.



As an example, lets do a "compression" on an image of the American Flag. The Flag has a field of blue at the upper left with stars in it and red and white stripes that are to the right of and below the blue field.



Compression will start with the upper left corner of the flag. The blue field is one hunded pixels across till it reached the first stripe. Currently, each pixel occupies one information slot in our file. A compression program may look at the flag and decide that it can represent the first line in a more compact way by noting that the color blue extends for 100 pixels and encoding it as "blue 100". Now, instead of taking up 100 slots to create the first blue line, only two slots are used, one for the color, another for the number of pixels. So you can see, we have compressed the fist line by 98%.



When it is time to display the Flag, the program will read the compressed file and will add 100 blue pixels to the top corner, thus uncompressing the file.



This is an overly simplified way of explaining it and the math is far more complicated but I think this will give you the general idea of how file compression works.

Answer 4

A file is made up of bits. Compressing a file merely means that you're running a set of complex (but reasonably well-known and easily-reversable) equations on the bits inside of the file to squeeze them down so that there are fewer of them total -- but they won't be accessible until you reverse that compression equation. Fortunately, you've got this computer to keep track of these things for you.



Consider the phrase "They are" -- now we humans can compress that by saying that a space followed by the word "are" can be reduced to "'re", such that "They are" compresses to "They're". And to undo that, we just find the "'re" and replace it with " are". Same deal with computers and compressing files, just far more complex. Note that this is "loss-less" compression because we can get back all of the original content that we compressed.



Now, getting tangental, think about music or movie trailers that you can listen to or watch over the web. Those have original data which is vast and huge and would take forever (okay, less than forever these days -- but still a really long time!) to transmit. The compression that happens on those bits of media is more aggressive than what happens to mere files: It starts off with something like "A scenic image of a grand mountain overlooking a fruited plain" and as part of its compression, it loses some of the details so that we're left with something like "An image of a mountain overlooking a plain" which we then compress in a more conventional fashion before transmitting it over the web. This is called "lossy" compression because it loses some of the original content. If you watch a small-resolution trailer full-screen on your monitor, it will become very evident that a lot of the image has been lost in compressing the data down as small as it could go. (Alternately, you can look for this in patches of near-solid color on DVDs which are compressed using something along the lines of MPEG-4 video compression. It's harder to see, but it is there.)

Answer 5

Well, Matthew is right, you can compress files to make them smaller or to combine number of files into a single file. this makes it easy to manage heaps of data and send in a single email message. So you dont have to delete important data from your hard drive to create some space, you can simply compress file or zip the files to save disk space. There are many users who compress files to send the files quickly over the internet. Compressing the file is useful as it reduceing the consumption of expensive resources that includes hard disk space or transmission bandwidth. However, it is important to note that in order to use the data that you receive in compressed format, you need to decompress it.

Answer 6

Compressing a file is basically encoding data to take up less storage space and less bandwidth for transmission. Digital data are compressed by finding repeatable patterns of binary 0s and 1s. The more patterns can be found, the more the data can be compressed. Text can typically be compressed to approximately 40% of its original size, and graphics files from 20% to 90%. Some files compress very little. It depends entirely on the type of file and compression algorithm used (see archive formats).

Answer 7

From How Stuff Works:

http://www.howstuffworks.com/file-compression.htm

Answer 8

compresssing a file basically means that u r saving u'r disc space. programs like win zip and win rar provide compressed files. U can also host sumtin on the net easily if u have a compressed file so therefore its way faster

Answer 9

Yes. You can use a program called WinZip to compress a file into a .zip.



See this website for instructions on how to zip a file: http://www.eurekais.com/brock/aazip.htm#create

Answer 10

I think it's another way of saying shrink a file. I guess it's like compacting trash

Answer 11

http://www.7-z.org/



http://www.google.com/search?btnI=I%27m+Feeling+Lucky&q=wiki+file+compression