1. Internal modem
Internal modem is cheaper than external one but its installation is more difficult. Internal modem is a modem device that is placed into a single unit with the motherboard on the system CPU unit. Internal modem can not be moved from one computer to another computer dirrectly (we must open the CPU casing).
2. External modem
External modem is easier in installation and can be moved from one computer to another easily (without opening the CPU casing), safe from lightning, but its price is more expensive.