FTP (File Transfer Protocol) is used to transfer files from one machine to another. It is a standard network protocol that allows for the transfer of files over a TCP/IP network, such as the internet. FTP is widely used for transferring files between a client and a server, enabling users to upload, download, and manage files remotely.

Below are the key details explaining why FTP is used for file transfer:

FTP Protocol:
The FTP protocol operates on the client-server model, where the client initiates a connection to the server, and the server responds to the client's requests. The client can request to upload files to the server or download files from the server. FTP uses separate control and data connections for communication.

Key Features of FTP:
1. Authentication: FTP provides authentication mechanisms to ensure secure access to files. Users need to provide valid credentials (username and password) to connect to an FTP server.

2. File Management: FTP allows users to perform various file management operations such as creating directories, renaming files, deleting files, and changing file permissions.

3. ASCII and Binary Mode: FTP supports two transfer modes - ASCII and Binary. ASCII mode is used for transferring text files, while Binary mode is used for non-text files like images, videos, and executables.

4. Passive and Active Mode: FTP can operate in two modes - Passive and Active. In the Passive mode, the client initiates both the control and data connections, while in the Active mode, the server initiates the data connection.

Advantages of FTP:
1. Wide Compatibility: FTP is supported by most operating systems and can be used with various FTP client software.

2. Efficient File Transfer: FTP allows users to transfer large files quickly and efficiently. It supports resuming interrupted transfers, making it suitable for unreliable network connections.

3. Remote Access: FTP enables users to access and manage files on remote servers, providing flexibility and convenience.

4. Security: Although FTP itself does not provide strong encryption, secure versions like FTPS (FTP over SSL/TLS) or SFTP (SSH File Transfer Protocol) can be used to ensure secure file transfers.

Conclusion:
FTP is the preferred protocol for file transfer due to its wide compatibility, efficient transfer capabilities, and remote access features. It provides a reliable and convenient method for transferring files between machines over a network.