A download refers to the process of retrieving data from a remote source. The most common type of download is someone accessing a file from a server on the Internet; but downloading does not exclusively refer to files retrieved from the Internet. On the Internet, the most common servers to download data from are an:
Each of these servers use a different Internet protocol, and each of these protocols are a part of the Internet protocol suite. For example, web servers will use HTTP (protocol), email servers will use POP and SMTP (protocols), and ftp servers will use FTP (protocol). Each of these protocols, which are used to download data across the Internet, are part of the application layer of the Internet protocol suite. These protocols will work in tandem with other protocols within the Internet protocol suite: most notable TCP (protocol).
Downloading from the Internet is based upon a client-server model. Which means a client program will request data from a server using one of the protocols highlighted above. Web browsers are an example of a client platform; which use HTTP to download webpages from web servers. Email client programs, like Outlook Express, use POP and SMTP to download email messages from mail servers.
Downloading data is an integral part of the Internet and the World Wide Web. When users surf the World Wide Web, they are continually downloading data stored on Web servers: html files, image files, video files and sound files. The first ever web server was a 'NeXT' computer; connected to the Internet by Tim Berners-Lee (the inventor of the Web).
Downloading data from FTP servers (File Transfer Protocol) predates the World Wide Web. Client programs, like file sharing programs, typically use FTP to enable their users to download and upload files. Some of the most common files downloaded from FTP servers are: software (freeware, shareware), software updates, patches, multimedia files, pictures, podcasts and text documents.
The speed at which a download can be made is dependent upon the file server (where the file is stored) and the download speed of the user's Internet connection. Downloads are usually recorded in bits, bytes, kilobytes and megabytes.
An alternative to downloading is streaming (via webcasts and other means). Streaming enables users to access data (usually video) "on the fly"; without having to save it as file. This has the advantage of users being able to view the content immediately - without having to download the whole file and then view it - and also saves storage space. Youtube is a prime example of a streaming service.
To download files, a user requires a client program to connect to the servers which store the file and retrieve it to the client program. Client programs usually have a specific purpose: for example, a file transfer client, like WS_FTP, can transfer files to FTP and web servers (they can upload/download files in ASCII and Binary format). Whereas, an email client program, like Outlook Express, will only retrieve email messages from mail servers.
The most popular client program for downloading files from the Internet is a web browser; which, as you would assume, downloads files (webpages, images etc) from web servers using HTTP. Some web browsers support a range of Internet protocols, and can download files from file, email and web servers.
Downloading data using a web browser is extremely easy to do:
The above image shows a typical browser menu; which appears when a user right clicks (with a mouse) a hyperlink. The 'save target as' allows user to download a range of files. Downloading files is essential for making a backup of important files. The primary task of a web browser is to browse web pages. Download managers, within browsers, tend to be simplistic; if the download fails, they cannot recover the download from the error point. Users can, however, purchase a professional download manager, which can pause and resume downloads, resume broken downloads, schedule downloads and find mirror sites if the current download provider is offline.
When you download software files, you may find that the file has been compressed. File compression saves space on servers. If you have downloaded a file which is compressed: you will need an application which is capable of decompressing the file. Winzip is a prime example of such an application: which can decompress (unzip) the zip file format. Zip is the most popular type of file compression. Compressed files are sometimes referred to as an archive file; due to it including numerous files compressed into one file.
Some other popular file formats, and their corresponding file extension: