Unlike people and animals, the rover brains are in its body. The rover computer (its "brains") is inside a module called "The Rover Electronics Module" (REM) inside the rover body. The communication interface that enables the main computer to exchange data with the rover´s instruments and sensors is called a "bus" (a VME or Versa Module Europa bus to be exact). This VME bus is an industry standard interface bus to communicate with and control all of the rover motors, science instruments, and communication functions.
Better memory than ever
The computer is composed of equipment comparable to a high-end, powerful laptop computer. It contains special memory to tolerate the extreme radiation environment from space and to safeguard against power-off cycles so the programs and data will remain and will not accidentally erase when the rover shuts down at night.
On-board memory includes 128 MB of DRAM with error detection and correction and 3 MB of EEPROM. That´s roughly the equivalent memory of a standard home computer. This onboard memory is roughly 1000 more than the Sojourner rover from the Pathfinder mission had.
Better "nerves" for balance and position
The rover carries an Inertial Measurement Unit (IMU) that provides 3-axis information on its position, which enables the rover to make precise vertical, horizontal, and side-to-side (yaw) movements. The device is used in rover navigation to support safe traverses and to estimate the degree of tilt the rover is experiencing on the surface of Mars.
Monitoring its "health"
Just like the human brain, the rover computers register signs of health, temperature, and other features that keep the rovers "alive."
The software in the main computer of the rover changes modes once the cruise portion of the mission is complete and the spacecraft begins to enter the Martian atmosphere. Upon entry into the Martian atmosphere, the software executes a control loop that monitors the "health" and status of the vehicle. It checks for the presence of commands to execute, performs communication functions, and checks the overall status of the rover. The software does similar health checks in a third mode once the rover emerges from the lander.
This main control loop essentially keeps the rover "alive" by constantly checking itself to ensure that it is both able to communicate throughout the surface mission and that it remains thermally stable (not too hot or too cold) at all times. It does so by periodically checking temperatures, particularly in the rover body, and responding to potential overheating conditions, recording power generation and power storage data throughout the Mars sol (a Martian day), and scheduling and preparing for communication sessions.
Using its "computer brains" for communications
Activities such as taking pictures, driving, and operating the instruments are performed under commands transmitted in a command sequence to the rover from the flight team.
The rover generates constant engineering, housekeeping and analysis telemetry and periodic event reports that are stored for eventual transmission once the flight team requests the information from the rover.
To find out more about how the rovers "talk" to engineers back on Earth, see the Communications section.