download

Download is the transfer of data from a remote system to a local device. In common use, it refers to saving a copy of a file from a server, website, or peer to a local computer, smartphone, or other device. The term contrasts with upload, which sends data from the local device to a remote one. A downloaded item can be software, media, documents, or other data, and is usually stored in a user-chosen location before use.

How downloads operate depends on the protocols and software involved. A client requests data from a server using HTTP or HTTPS, or from an FTP or SFTP server. The server responds by sending the file, which the client saves to disk. Modern systems support resuming interrupted downloads via range requests, so a partially downloaded file can be resumed later. Integrity is checked with checksums or digital signatures to detect corruption or tampering.

Common download methods include direct downloads from a single source, and peer-to-peer downloads such as BitTorrent, which obtain pieces from multiple users. Applications may include a download manager to accelerate transfer, organize queues, or manage retries. Large distributions, like operating system ISOs or software updates, are frequently delivered via dedicated update services or app stores, sometimes using content delivery networks to improve speed.

Security and legality are important considerations. Downloads can carry malware or unwanted software, so users should obtain files from trusted sources and verify checksums or signatures. Copyrighted content may be restricted to legitimate channels, and unauthorized downloading may violate laws or terms of service.

Historically, downloads began with file transfer protocols such as FTP and Usenet, becoming widespread with the World Wide Web in the 1990s. The development of bandwidth-efficient and decentralized methods, like BitTorrent in the early 2000s, further shaped how large files are distributed online.