[zxter]

There’s no issue with a computer recognizing two keyboards, but smaller keyboards often lack all the keys found on a standard one. So, you’ll need to use modifiers to create the keystroke and then send it to the computer. If you press a modifier on one half, the other half needs to be aware of it to send the final keystroke. Creating a layout with these modifier-based key combinations is just a small part of the many tricks you can pull off with custom firmware. While the computer thinks it’s connected to a standard keyboard, you can do some really deep customization on the keyboard side.

[varispeed]

Wouldn't operating system take care of that?

[zxter]

When you have two halves of a keyboard recognized as separate keyboards by the computer, then just like you said. For example, if you press shift on the left half and u on the right, the computer first sees the shift and then the u. It then types a capital U.

But in my case, let's say I don't have any numbers on the keyboard. Instead, I use modifier keys to create a layer for numeric values. So, when I press a modifier on the left, the computer won't notice. Then, pressing what would normally be the U key on the right sends a 7 instead. The computer just sees a 7 being pressed.