A download manager is a computer program dedicated to the task of downloading (and sometimes uploading) possibly unrelated stand-alone files from (and sometimes to) the Internet for storage. This is unlike a World Wide Web browser, which is mainly intended to browse web pages, composed of a multitude of smaller files, where error-free moving of files for permanent storage is of secondary importance. (A failed or incomplete web page file rarely ruins the page.) The typical download manager at a minimum provides means to recover from errors without losing the work already completed, and can optionally split the file to be downloaded (or uploaded) into 2 or more segments, which are then moved in parallel, potentially making the process faster within the limits of the available bandwidth. (A few servers are known to block moving files in parallel segments, on the principle that server capacity should be shared equally by all users.) Multi-source is the name given to files that are downloaded in parallel.
Download managers commonly include one or more of the following features:
Pausing the downloading of large files.
Resuming broken or paused downloads (especially for very large files).
Downloading files on poor connections.
Downloading several files from a site automatically according to simple rules (file types, updated files, etc. - see also Offline Browser).
Automatic recursive downloads (mirroring).
Scheduled downloads (including, automatic hang-up and shutdown).
Searching for mirror sites, and the handling of different connections to download the same file more quickly (segmented downloading).
Variable bandwidth usage.
Automatic subfolder generation.
Download managers are useful for very active Internet users. For dial-up users, they can automatically dial the Internet Service Provider at night, when rates or tariffs are usually much lower, download the specified files, and hang-up. They can record which links the user clicks on during the day, and queue these files for later download. For broadband users, download managers can help download very large files by resuming broken downloads, by limiting the bandwidth used, so that other internet activities are not affected (slowed) and the server is not overloaded, or by automatically navigating a site and downloading pre-specified content (photo galleries, MP3 collections, etc.) this can also include automatically downloading whole sites and regularly updating them (see Mirroring).
Many download managers support Metalink, an XML file listing mirrors, checksums, and other information useful for downloading.
