Sharing expansion device, controlling method and computer using the same

A sharing expansion device, wherein a computer has at least one first user account and a second user account, the first user account has been logged in the computer, the computer is connected to a first input device and a first monitor, the first input device is used for providing at least one first command, and the sharing expansion device comprises:

• at least two first ports used for connecting the computer and a second input device, wherein the second input device is used for providing at least one second command, and the computer executes the first command and the second command by way of time division multiplexing;
• a second port used for connecting to a second monitor, wherein the computer provides a first frame to the first monitor according to the first user account and provides a second frame to the second monitor according to the second user account;
• a hub unit used for connecting the first ports and the second port;
• and
• a graphic processor used for processing the second frame.