If you have an older SGI that has the DB15 keyboard connector, and you don't have any classic SGI keyboards (pre PS/2) there are some options.
https://www.drakware.com/
Drakware has a "Indigo to USB" adapter that works on all pre-PS/2 SGIs. You just have to go from DB15 to DIN6 (for the drak adapter).
Here is a diagram I created to do that. You can by a PS/2 extension cable from Amazon and cut it in half, using the Male segment. You can also get a DB15 male connector.
This works great in my 4D/320.
https://www.drakware.com/
Drakware has a "Indigo to USB" adapter that works on all pre-PS/2 SGIs. You just have to go from DB15 to DIN6 (for the drak adapter).
Here is a diagram I created to do that. You can by a PS/2 extension cable from Amazon and cut it in half, using the Male segment. You can also get a DB15 male connector.
This works great in my 4D/320.