A compressed folder is a single computer file that can contain many items, which it stores in a way that can reduce the total amount of disk space required. Although there are multiple types of compressed folders, the most common type is the ZIP compressed folder, which is compatible with multiple operating systems. Compressed folders have many advantages because they allow users to store several items within one file, which makes it much simpler to send multiple files in an email or file transfer application.
The extent of compression that compressed folders can use depends on the files contained within the folder. If a file was already compressed before it was added to a compressed folder, the file size will probably not be reduced further. This is common with compressed videos and images but can occur with various other types of already compressed files. There are also many different types of software available for compressing files, and some software lets the user specify a level of compression to use. One must keep in mind, however, that highly compressed files can take longer to extract than files using the default level of compression.
ZIP is the most popular type of compressed folder and can be used with most operating systems utilized by home and business users. Other formats also are used for storing files much like a ZIP folder does, and some are used for operating system and software installation packages. Each type of compressed folder format can use a different algorithm for compressing the folder's contents. Roshal Archive (RAR) and International Organization for Standardization (ISO) files are common formats, with RAR files being used for storing files and ISO files being used for disk images of CDs and DVDs. Operating system and software installation packages often use Cabinet (CAB) and Tar Gunzip (TGZ) files to package installation components together.
In addition to being useful for shrinking file size and for sending multiple items in one file, a compressed folder provides additional advantages. Many types of software for creating compressed folders let users require a password for opening the file. Compressed folders are especially useful for transporting and sharing files across operating systems, because there are many open-source and commercial utilities for opening the file on most common operating systems. Most operating systems support at least the ZIP format and have built-in utilities that can extract the folders without the need for additional software.