PuTTYCyg

PuTTYCyg is an ancient fork of PuTTY with Cygwin pseudoterminal support added.

Why?

Terminal emulators based on PuTTY has the minimum perceived latency on Windows. Besides, the actual latency is on par with that of Mintty.

As WSL2 has been widely used after its inception, Cygwin has become more and more of a relic. But it nontheless has excellent interoperablity, and it is independent of hardware virtualization, which quite a lot messes with the thermal settings of typical consumer machines. If you want a noiseless Unix experience on Windows before relying on SSHing into remote machines, give Cygwin a try.

Cygwin has its own pseudoterminal concept analogous to the Unix one. To interact with PTYs in Cygwin, one has to use one of the following ways:

• Bridge the Windows console subsystem against the Cygwin PTY layer. This is what ConEMU etc. are using. This approach hurts latency as there is one more layer of indirection, and the ConPTY subsystem is not always performant and reliant, as well.
• Directly leverage and thereby present a virtual terminal, using the Cygwin PTY layer. Mintty, the official terminal emulator of Cygwin, uses this approach. This has the benefit of less terminal input / output latency, with the added burden of behaving like a real terminal emulator. Latency management in said effective terminal emulator is indeed of concern.
• Directly utilizing the Windows console subsystem. Using ConPTY counts as a variation of this approach as well. It has the least theoretical latency due to a more direct connection with Windows conhost at a lower layer. The real deal-breaker lies in the natural limitation of the Cygwin console devices /dev/cons*: program manipulating user sessions, such as screen and tmux, refuses to function in such environments, rendering terminal workflows cumbersome to many.
• Translate the console into SSH. A working sshd is needed for this scenario, which complicates terminal handling and requires a background service to be running. sshd contributes to latency as well. The official PuTTY guide now recommands running psusan compiled under Cygwin to provided a bare SSH connection without the authentication layer, offering all niceties the SSH protocol support. But this still requires a background process even more harder to manage than sshd, as Cygwin is too integrated into Windows to provide an independent process management daemon.

PuTTYCyg solves this problem in a hybrid approach. A helper program cthelper.exe is born to bridge the Cygwin PTY layer to sockets understood by the modified putty.exe, which could generally exhibit a more stable latency profile thanks to the seemingly more stable nature of sockets in terms of latency and the customized terminal emulator layer of PuTTY.

From the subjective experience of the author, vanilla Mintty suffers from a high variance of latency; that is, cannot reliably predict how long the character would be inputted after hitting the corresponding key using muscular reflection when typing fast. Said problem persists even with ConPTY enabled, to which PuTTY is immune, perhaps because of its different implementation.

NOTE: As PuTTYCyg is an ancient fork, all remote functionality has been stripped out for security reasons.

How to build?

1. Install 32-bit MinGW toolchain in Cygwin. 64-bit toolchain untested but supposed to work.
2. At the top directory of the source code, run build.sh.
3. Put the resulting putty.exe and cthelper.exe in the same directory, and execute putty.exe to start PuTTYCyg.

But cthelper.exe can't find the Cygwin root directory?

Put it under /bin. This is due to the root directory detection mechanism of Cygwin, please consult the documentation.

TODO: cygbuild and integration into the official Cygwin package directory. If any Cygwin maintainer wants to make this an official Cygwin package, I'm really glad to help!

References

Thanks zewt@github for their excellent cutting down on PuTTY. https://github.com/zewt/puttycyg