They're used by ISO 2022 in general. Free version: https://www.ecma-international.org/publications/standards/Ec...

Of course Unix didn't interpret them; the terminal did.

Linux does do something with SI and SO, at least on the actual framebuffer console. It enables the VT100 alternate character set, for drawing things.

The k,l,m,n,o,p,q,r,s,t,u,v,w keys then become useful for drawing lines

If you have a linux desktop, switch to an actual console (Ctl-Alt-F1), then:

echo -e \\x0E

And type a bit of lowercase characters between k and w. To get the terminal back to normal:

echo -e \\x0F

That's what the VT100 did with SI and SO. It's been 30? 35? years since I touched a VT100, but I think I recall there being a configuration bit to enable alternate character set on SI/SO.

Here you go: http://www.pcjs.org/devices/pcx86/machine/5170/ega/2048kb/re...

Probably not what you used to use, but "ctty com2" (and a couple of Returns directed at the VT100) will make it "go." I'm not 100 on what the keymapping is when you're in the setup screen (virtual Setup key at bottom-left).