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PuTTY is a free SSH, Telnet, Rlogin and SUPDUP client for Windows systems.
If you already know what SSH, Telnet, Rlogin and SUPDUP are, you can safely skip on to the next section.
SSH, Telnet, Rlogin and SUPDUP are four ways of doing the same thing: logging in to a multi-user computer from another computer, over a network.
Multi-user operating systems, such as Unix and VMS, usually present a command-line interface to the user, much like the ‘Command Prompt’ or ‘MS-DOS Prompt’ in Windows. The system prints a prompt, and you type commands which the system will obey.
Using this type of interface, there is no need for you to be sitting at the same machine you are typing commands to. The commands, and responses, can be sent over a network, so you can sit at one computer and give commands to another one, or even to more than one.
SSH, Telnet, Rlogin and SUPDUP are network protocols that allow you to do this. On the computer you sit at, you run a client, which makes a network connection to the other computer (the server). The network connection carries your keystrokes and commands from the client to the server, and carries the server's responses back to you.
These protocols can also be used for other types of keyboard-based interactive session. In particular, there are a lot of bulletin boards, talker systems and MUDs (Multi-User Dungeons) which support access using Telnet. There are even a few that support SSH.
You might want to use SSH, Telnet, Rlogin or SUPDUP if:
You probably do not want to use SSH, Telnet, Rlogin, or SUPDUP if:
This list summarises some of the differences between SSH, Telnet, Rlogin and SUPDUP.
The Internet is a hostile environment and security is everybody's responsibility. If you are connecting across the open Internet, then we recommend you use SSH. If the server you want to connect to doesn't support SSH, it might be worth trying to persuade the administrator to install it.
If your client and server are both behind the same (good) firewall, it is more likely to be safe to use Telnet or Rlogin, but we still recommend you use SSH.
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