Download manager

Download manager
"Download accelerator" redirects here. For the specific proprietary program for Windows, see Download Accelerator Plus.
A download manager is a computer program dedicated to the task of downloading (and sometimes uploading) possibly unrelated stand-alone files from (and sometime 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.

Features
There are several things that some web browsers are not very good at. That's where the download managers enter the equation:

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).
Download managers are useful for active Internet users. For dial-up users, they can automatically dial the internet service provider at night, when rates or tariffs are usually 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.

See below for some examples of commonly used download managers. Some downloaders are optimized for a certain function. For example, Offline Explorer is designed to download entire websites.

Download managers, such as Go!Zilla, were among the first adware applications displaying a banner ad in the user interface.

Related to download managers are two other breeds of Internet programs, file-sharing peer-to-peer applications (Kazaa, eMule, BitTorrent, Gnutella) and stream recorders (such as StreamBox VCR).

While download managers are designed to give users greater control over downloads, some downloaders are created to give that control to content distributors instead. Some software companies, for example Adobe [1], provide such downloaders for downloading software on their own site. Presumably this increases reliability and reduces tech support costs to them. A possible reason is increasing the control over redistribution of their software (even when the software is freeware).