http://www.ozvalveamps.org/zipfiles.htm | Created: 24/08/07 | Last update: 12:25 5/01/11
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ZIP file FAQ

What, why, how?

Update: 17/3/09
Zip tools for Mac users


What is a ZIP file?

A ZIP file can be thought of as a single file that acts like a directory folder - you can put other files and folders inside it. They can be recognised from the name format “filename.ZIP”.

There have been many different methods of compressing files but ZIP has evolved into a defacto standard with many free tools available.

ZIP files do two basic things, they compress a file so it takes up less storage space and less time to transmit, and they bind groups of files together into a single file package.

There are a huge number of confusing options for using ZIP files for backup, archives, and tuning for speed and size, data privacy, and whatnot; but Don't Panic, default operation is very simple and useful.



Why ZIP files?

o Size - is not as important as it once was, so the primary reason for ZIP files, compression or lossless reduction in storage size, has become secondary, but still useful in many applications. (Unlike compresssion formats such as MP3 which throw away “unimportant” data, ZIP restores the file with 100% bit accuracy.)

Some file formats, such as “*.DOC” files produced by wordprocessors, contain a huge amount of redundant information and will compress very dramatically to perhaps one-tenth for storage or transmission.


o Binding - files together in a single package is now the primary usefulness of using ZIP. There are many reasons why you might want to bind a group of related files together, text, pictures, drawings, soundfiles, webscripts and so on that perhaps might only work properly as a package.

In my case people are sending me multiple photographs as e-mail attaches, and the overhead in downloading each one individually generally far exceeds the time to actually transfer the file. When multiple files are bound in a single ZIP file what literally takes hours then only takes minutes.

Note that sound and image formats such as MP3/MPEG, JPG and GIF are already a compressed format and will not further compress, in fact may get a tiny bit bigger.


o Integrity - of the file package. What you pack is what they get. As long as you pack it properly, everyone who gets your ZIP gets the entire package, and it is protected against most viral infections.

There is a particular problem sharing the work on a website where HTML scripts have to be exchanged. E-mail systems tend to pry into your mail, and mostly this is good because it helps to protect us from spam and viruses.

But it's not so good when a book arrives by post, and rather than just delivering it, the 'postie' opens the package and starts reading it to you. And that's what Yahoo mail does with simply attached HTML script files. I don't want Yahoo's interpretation of Macbeth, I just want it to hand the script over intact. And that is what it does with a ZIP file.

A ZIP file can be used as a protective shell for files you don't want fiddled with in transit. There is also an option that only verifies a ZIP file is intact.


o Privacy - is sometimes a concern, and ZIP files may be password protected to prevent idle prying. But take careful note that there are effective tools out there specifically for cracking ZIP file passwords, and that this system isn't proof against even a low-level determined assault.


o Backup/archive - options are provided that should cover just about any periodic backup scheme, and there are a large range to cater for this type of use.

Additionally, ZIP files allow you to include a comments screen that shows every time the ZIP file is opened.



How do I make a ZIP file?

Tool

First you need a ZIP tool. To open, view, add, extract or delete a file from within a ZIP file you have to have a ZIP tool or programme.

If you have a Windows computer you may already have WinZip on your machine. Use Start/Programs to see if WinZip is already shown.

Diagnostic 1: use Start/Find/Files Named “winzip”. Mine is called “Winzip32.exe”. You will want to create a desktop icon or include a shortcut in the start menu in the normal manner.

Diagnostic 2: use Start/Find/Files Named “*.ZIP” to find any ZIP file on your machine. Once one is found, stop the search, and double-click on it. If you are lucky WinZip will start and ask about registering with a slightly alarming window. Simply click on “I Agree” at the bottom. That's it.

While it is legally limited to a 45-day evaluation period, and has the startup nag screen, WinZip is fully functional and not cripple-ware.

If you don't have it, you can download it free from WinZip.com.

There are also other tools available such as PKZIP that are a bit less user-friendly but just as functional.

Method

The first step is to define the ZIP file name and where, in which folder, it will end up. I have a folder specifically for building ZIP files which saves thinking about it and doubles as an archive of created ZIP's.

The tricky part here is creating a name for your ZIP file that represents it's contents, somewhat like a folder name.

Once you have a name and location for your ZIP file the second step is a very simple matter of dragging and dropping files from the file Explorer into the WinZip window. This will bring up the add dialog window, and normally the default setting will be okay, so simply click on the Add button.

Note that if your selection includes a folder that this folder complete with it's contents including any sub-folders and their contents, will be added to the ZIP file. These files will then appear as if combined into a single folder, but the file/folder structure is preserved so that when the files are extracted again the original file/folder structure will also be recreated identical to the original.


Some Zip tools for Mac users

(these are untested by me, so reviews and other links are very welcome)

Info-ZIP Home Page
MacZip - a combination Zip/UnZip graphical front end for Mac OS.

YemuZip - Free Zip Tool for Mac OS X

ZipIt: Macintosh compression utility
ZipIt is a Macintosh program that zips and unzips archives in a format fully compatible with PKZip for the IBM and zip implementations on other systems.

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