Understanding File Compression and Archives
Lawrence Abrams
- July 17, 2005
- Read 81,022 times
Table of Contents
File compressors and archives?
This tutorial will focus on explaining what file compression and archives are and how to use them. This technology will not only enable you to more efficiently send attachments via email, but also save space on your hard drive and allow you to more easily back up files. To begin, lets discuss some of the terminology that will be used in this tutorial.
- File compression is the act of taking a file on your hard drive and making it so that it's size becomes smaller and therefore takes up less storage space and is faster to upload or download on a network or the Internet.
-
File Compressor - A compressor is a program that actually compresses another file. Compress, Gzip, WinRar, and Winzip, among many others, are examples of these types of programs.
-
File Archival Program - An archival program takes many seperate files and archives them into one file. For example, an archival program would allow you to take a directory of files and archive them into one file that you can then send as an email with a single attachment for all those individual files.
-
Archive - An archive is a single file that contains many seperate files. These individual files can be extracted from the main archive
-
Compressed File - A file that has been compressed into a smaller size than it originally had.
It is important to note that many programs can both archive and compress files. For example, Winzip will take many seperate files, compress them and then store them into an archive file. Thus you are left with a single archive which contains many compressed file.
When to use an archive or file compression
Now that you know what a compressed file or an archive is, you must be asking yourself why you would want to use them. The three most common reasons to use archives and compressed files are:
File compression saves storage space
By using a compressor to make an image smaller, you are using up less space on your hard drive to store this file. For example, a word document that is 89 Kilobytes on my hard drive, when zipped, is now only 8 Kilobytes. That is a 90% saving in storage space! Take a look at the table below to see some more examples of the type of storage space you can save using file compression:
|
Type of file
|
Size before compression in Bytes
|
Size after compression in Bytes
|
Percentage Compressesd
|
|
|
|
|
|
| Word Document |
89,600
|
8,959
|
90%
|
| TXT File |
29,978
|
10,476
|
66%
|
| Excel Document |
109,056
|
89,816
|
18%
|
| EXE File |
66,048
|
34,757
|
48%
|
| DLL File |
260,096
|
121,155
|
53%
|
| JPEG Image |
1,093,504
|
1,092,040
|
0%
|
| Bitmap Image |
4,854
|
4,854
|
0%
|
| GIF Image |
47,924
|
47,825
|
0%
|
| MP3 File |
5,234,688
|
5,134,985
|
2%
|
As you can see, some file formats compress a great deal more than other formats. This is because certain file types are already compressed, and therefore can not be compressed any further. Looking at the chart above, it obviously does not make sense to compress MP3, GIF, JPEG, or other compressed file formats as you will not gain any benefit. On the other hand, Word, Excel, Text, and program files compress quite well
Transmission Speeds
How fast a file is transmitted over a network or the Internet is dependent upon how big this file is. For example, a file with the size of 1,337,344 bytes took approximately 28 seconds to upload to a remote server. Yet this same file compressed to a size of 554,809 bytes only took 12 seconds. That is a savings in time of over 50%. Now imagine you were sending files that would normally take an hour to send, and after compressing the files, it now only takes 30 minutes. The savings in time and potentially money is incredible.
Sending only 1 file
There are times that you need to send many attachments in one email message. This can be difficult and confusing at times, so instead you use an archival program to convert the 20 files into a single file. This is much more organized and easier to manipulate.
Backing up data
Archival programs are used often to back up data. You would use archives to backup a folder or a number of files into a single file and compress them as well. This allows you to save space and then store that individual file on a floppy or other removable media.
Note: It is important to note though, that with all formats, whether it be a compressed file or an archive, you must always uncompress and/or extract the file before you will be able to use it.
Types of archives and file compressors
There are many types of archival progarms and compressors. The table below will give a listing of the more common programs that are used today along with the file extension that they use:
|
Program*
|
File Extension
|
Type
|
Operating System**
|
| WinZip |
.zip
|
Archive/Compress | DOS/Windows |
| WinRar |
.rar
|
Archive/Compress | DOS/Windows |
| Arj |
.arj
|
Archive/Compress | DOS/Windows |
| Gzip |
.gz
|
Compress | Unix/Linux |
| Compress |
.Z
|
Compress | Unix/Linux |
| TAR |
.tar
|
Archive | Unix/Linux |
| Stuffit Expander |
.hqx
|
Archive/Compress | Apple |
* Many of these programs can handle more than one format. The format listed is the native format for that program.
** The operating system listed is the native operating system for these formats. These formats may be able to be used on other operating systems as well.
Now that you understand file compression and archiving, download some of the above programs and play around with them. They are very easy to use and understand. For detailed instructions on creating Zip files, visit the following tutorials:
How to create and extract a Zip File in Windows ME/XP/2003
How to create and extract a ZIP File in Windows 95/98/2000
As always, if you have any questions, please feel free to ask them in the computer help forums.
--
Lawrence Abrams
Bleeping Computer Basic Computer Concept Tutorial Series
BleepingComputer.com: Computer Help & Tutorials for the beginning computer user.
