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Understanding ZIP Files

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#1
alandemartino

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Understanding ZIP Files

What is a ZIP archive?

Archives are files that contain other files. Typically the files in an archive are compressed. Archives usually have file names ending with ZIP, LZH, ARJ, or ARC, depending on how they were created. Archives make it easy to group files and make transporting and copying these files faster.

Typical Uses for Archives

Most files available in "file areas" on bulletin boards and electronic services like CompuServe and the Internet are distributed as archives. Two benefits of using archives for electronic file distribution are that only one file transfer operation ("download") is required to obtain all related files, and file transfer time is minimized because the files in an archive are compressed. It is often useful to send a group of related files to an associate. Rather than distributing individual files it is often easier to distribute the files as an archive to benefit from the file grouping and compression. Some files are important but not used often. To save disk space simply compress these files into an archive when they are not used, and decompress them only when needed.

What is a Self-Extracting ZIP File?


A self-extracting Zip file is an executable program file (.EXE file) that includes both a ZIP file and software to extract or "unzip" the contents of the ZIP file. Users can extract the contents of a self-extracting ZIP file by simply running it. This is convenient, because the end user does not need an unzip program to extract files from these self-extracting archives.

Archive formats

- ZIP files are the most common archive format.

- ARJ files are another popular archive format. ARJ files are manipulated by the ARJ program from ARJ Software.

- LZH files are manipulated by the LHA program from Haruyasu Yoshizaki. LHA won the October 1991 PC Magazine Editor's Choice award as the best data compression utility.

- ARC is an older format. ARC files can be manipulated by several programs, including the original ARC, ARCE (also known as ARC-E), PKXARC, and PKUNPAK.

- TAR, Z, GZ, TAZ, and TGZ files are often found on Unix-based Internet sites. The relationship between these file types is less straightforward than the afore mentioned file formats. TAR stands for "Tape ARchive". This is an old file format and does not provide compression; it is used only to group files. Z files are compressed with gzip or the older Unix "compress" program. GZ files are gzip files. Z and GZ files cannot contain multiple files. TAZ and TGZ files are TAR files compressed in "Z" or "GZ" format.

- UUencoded, XXencoded, BinHex, and MIME files are used primarily to transfer binary files by Internet e-mail. If you encounter one of these files, you can open it and extract its contents with WinZip.

- LZEXPAND format is a Microsoft compressed format. However, there are several variations on this format, and Microsoft has not released documentation on these variations. Therefore, you are limited to decompressing files supported by your version of Windows (Windows for Workgroups supports some files not supported by Windows 3.1). Microsoft Compress files usually end with a trailing underscore, for example "commdlg.dl_". Like Z and GZ files, Microsoft Compress format files contain only one file. This format is used for many files on your Windows 3.x distribution disks and many other Microsoft products. Note that not all files ending with an underscore are Microsoft Compress format files.

Making a ZIP file

Most programs will let you ZIP or UNZIP from the right-click menu in Windows Explorer. You can select the 'Add to ZIP' option which will make a new archive for you in the root directory of where the file is located. That's all there is to it. If you want to add files to the archive, you can drag and drop any file from Windows Explorer into the ZIP filename. This will add the file to the archive. If you wish to delete a file from the archive, simply open the archive (double click on it in Windows Explorer) and select the file(s), then hit the 'Delete' button.

Unzipping (extracting) an archive

To extract an archive you can double click on the filename in Windows Explorer. This will launch the default associated ZIP program installed on your system and open the archive. You can then select any file or all files in the archive and hit the 'Extract' button to unzip the file(s). The ZIP program will ask you for directory to extract to, filename to extract and so on. Simply answer all queries.

Note:

Many files available for download on the Internet are self extracting executable (.exe) archive files.
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#2
nanaplough

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Hello. Am I wrong in understanding that by creating a .rar archive and then sending this as an email attachment, the file will be quicker to send.
At present I have only WinRar and the archived file stays more or less the same size as the original, resulting in the email taking a long time to send as the attachment uploads.
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#3
dsenette

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compression (zipping) is only an advantage when using files that are compressable (such as documents, text based files, certain kinds of images, etc...)... what you're doing when you "zip" a file is removing all the "extra stuff" from that file thereby compressing the file and making it smaller... in text documents when you use a compression program it will remove all of the blank spaces (carriage returns, spaces, etc..) and leave special information so that when it's uncompressed the spaces return, with images the program will tend to blend colors and remove white space to compress the image..

certain files, such as mp3s and jpgs are already compressed when they are created (if you look at your mp3 encoder of choice..you'll notice a setting for compression ratio) so they cannot be compressed any further by zipping them...which i would say is why your rar stays about the same size as the original files

any better?
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#4
nanaplough

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Yes I'm understanding thanks.
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#5
gmek_jj14

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hi.. i've just downloaded 2 split media files that are compressed but evertime i try extracting it an error occurs.
the error says

'Extracting to "C:\example\"
Use Path: yes Overlay Files: no
Error in file #1: bad Zip file offset (Error local header signature not found): disk #1 offset: 4'

i've tried extracting it both at the same time but the error says
'End-of-central-directory signature not found. Either this file is not a Zip file, or it constitutes one disk of a multi-part Zip file.'

please help me!!! thanx!
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#6
warriorscot

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THis is a how to guide as basic and incomplete as it is not a help thread please start another thread in an appropriate forum. Windows or applications would do.
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#7
gubester

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I need help with my zip files somehow i changed the format in which they open so now every time i try to open one of my zipped files it pops open vlc my media player I cant figure out how to get it to just go back to the default little zip folder any advice would be greatly appreciated.
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#8
skyhintack

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Hi and Welcome to Geeks to Go!

Because this is a Tutorial, it's not meant to be a place to answer questions. If you need help, please post a new thread in the appropriate forum. This will also help you to get a better, and faster response.

Thank you,
Sky
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#9
WheelsOH76

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Are .RAR files much different from .ZIP files or their close cousins? What about FLAC files? How do lossless compression types such as FLAC differ from the lossy kinds in their implementation?
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