How do I install an internal modem?

The main problem with producing such a modem was forwarding commands from the computer. This could be addressed in internal modems that plugged directly into the computer's motherboard. Such modems had access to the computer's main memory, and by dedicating certain memory locations (or registers) to various status readouts or commands, software programs running on the computer could control the modem. This was a straightforward and thus a popular solution; the Novation APPLE-CAT II for the Apple II computer was an early programmable modem of this type.