A.1.2 Why use PuTTY when I could use OpenSSH?

These days, Windows comes with a version of OpenSSH as an optional component of the operating system, and its command prompt windows are much more like Unix terminals than they used to be. So it's true that if you want SSH on Windows, you can use OpenSSH in a Windows terminal, and not have to install PuTTY at all.

We're not going to try to persuade you that you shouldn't use OpenSSH in preference to PuTTY. PuTTY is free software, in the ‘no cost’ sense as well as the ‘freedom’ sense – we don't get more money by having more users. PuTTY and OpenSSH have different feature sets, and different ways of doing things, and it's entirely up to you which you prefer.

A few examples of things you might like about PuTTY:

• a range of built-in options to log your session to a file
• a range of configurable tweaks to the terminal emulation
• a unified saved-session system that lets you customise your settings for a particular destination host, including the SSH-specific settings (like authentication) and terminal and logging setup
• access to mid-session configuration via the GUI, instead of stealing a key sequence from your remote terminal session. With the OpenSSH [Return][~][thing] system, you always have to remember it's there even when you're not using it, to avoid triggering it with input you meant to send to the server. In PuTTY, the corresponding facilities (like reconfiguring port forwardings) are done using the GUI menus, and all keystrokes typed into the window consistently go to the server.
• simply, different terminal emulation from Windows's one, which you might find works better for some remote applications. Or you might not, of course; it will depend on what kind of machine you're connecting to, and maybe your personal preferences. And many people will have no opinion either way.
• and, of course, support for things that aren't SSH. In particular, talking to serial ports instead of the network.

But if none of this impresses you, and you'd rather use Windows's version of OpenSSH, that's up to you.

Unix, of course, has always had OpenSSH, even before the Unix version of PuTTY existed. So this question has been relevant for much longer! When we first wrote the Unix port of PuTTY, people asked us why it was necessary. Partly the answer was that having the PuTTY code run on Unix too made it easier to develop in general (Unix had a wider range of better development and debugging facilities, and in my opinion, still does). But the same considerations as above also apply: on Unix too I use GUI PuTTY for my SSH connections, so that I never have to deal with that ~ business, and I use the Unix pterm for my local terminal sessions too.