I must be missing something here?

I assume you're talking about something like connecting the midi OUT of, say, a keyboard into the midi IN of, say, a sound module? Just like the two devices were designed to operate, and have done so since before the time of DAWs etc? Nothing else involved. And Windows, Mac or Linux totally irrelevant.

Or are you thinking of something else??

Geoff

Geoff, are you talking about connecting two devices with a cable?
What if one or both devices are virtual?

So, I WAS missing something!

You were thinking specifically of virtual devices, but omitted to mention this in your question?

To answer your question, yes, I was thinking of some sort of cable. Is there such a thing as a virtual cable?

At one time, not so long ago, I had a virtual keyboard active (VMPK), and Virtual Midi Synth system active, and these were working fine and no DAW was involved, and as far as I'm aware, no 'intermediate software' (although as it was all virtual I couldn't be sure about that). The two processes just connected, and got on fine, although I maybe had to do a tiny 'introduction'. Then I needed to change the HD and the VMPK is no longer active, but the Virtual Synth etc is still there (with SynthFont ?)

Geoff

VMPK has its own menu through which you can connect it to anything so it's more than just a MIDI port.
Another use case: ho do you connect devices that have no 5-pin DIN connectors, only USB?

Hello Sema,

I was not aware that VMPK was .a MIDI port', I'll have to look into that. The system is still on a HD here, just not active. I was using it as a virtual Keyboard to test Virtual Midi Synth. I would expect that any device like that, on any OS, would have an option to search for something to play through, and could connect if something is found.

As for the cables, on the basis of the devices that I have, some of which do have USB connectors as well as standard midi, the only functional difference between the midi cables abd the USB is that the USB handles both directions in the one cable. There may be a switch or even a software setting to select one or the other if the device has both systems. The little USB/MIDI adaptors we discuss here from time to time have a single USB connector on one end, and 2 midi connectors for IN and OUT at the other end.

Geoff

Thanks a lot Clemens Ladisch!

It's strange that Audio MIDI Setup on my Mac does not see some virtual ports ( opened with https://github.com/jazz-soft/midi-test )

Are there any indications that this will be solved with MIDI 2.0?

It is very limiting that on Windows you need an extra virtual MIDI Port, which causes more jitter and latency.
It's not even an option with all hardware. For example Ableton Push 2 Live Port.When it is connected to Ableton Live, you can't access that port from outside of Live.
So if you have an application that extends functionality of that controller in conjunction with Live, you can only do it on OSX.
Most intermediate MIDI Applications are based on RTP MIDI from OSX. Everything is copied except the ability to use a controller in 2 apps.

Sorry for kickin-in so late! I've just found this discussion that somehow I missed until now.

Windows lacks two features that both Linux and macOS natively include:

• Routing between MIDI ports. Sema asked about connecting two hardware MIDI devices together through the computer. It is possible in Linux and macOS, but Windows does not provide native tools and features for it, as Clemens correctly answered. For instance, you plug your MIDI Controller to an USB port in your computer, and want to produce sound with the native Windows synthesizer, the "Microsoft GS Wavetable Synth", or the better alternative "Virtual MIDI Synth". Those are soft-synths, but they are built as device drivers (with good reason, because the next limitation), so they appear as hardware MIDI ports to the operating system. The same would happen if the synth was a SoundBlaster Audigy card, or the old and beloved Yamaha XG.
  
• Virtual MIDI ports for software applications. In addition to the former limitation, this means that you can't connect two MIDI applications together in Windows. For instance: play music in VMPK and record its events in any DAW. This is trivially solved in Linux and macOS, because VMPK leverages the virtual MIDI ports available in Linux and macOS, but in Windows you will need something like the "loopMIDI" virtual cable by Tobias Erichsen to connect both applications.
  

I've written a blog post some time ago about the second problem: connecting the FluidSynth synthesizer to other things in Windows, macOS and Linux.