The first computer component runs all of the car's engine functions. It makes the car run smoothly and monitors fluid temperatures and fluid pressures, taking in an abundance of information from the sensors in the car, like how much oxygen is in the air. This way the car computer knows how much air to mix with its fuel for proper combustion. This part of the car's computer also measures temperature so it can distinguish whether or not it needs more coolant, or if it should turn on fans to cool down the engine.
Another component of car computer records engine data. For example, if your car is idling rough, the car's computer will record diagnostic codes for the mechanics to be able to determine exactly where the problem lies. This computer also records information if something is malfunctioning or needs to be replaced, which is often alerted to by a 'Check Engine' light. In this way, a mechanic can use the computer to check out any problems the car might be having, like with emissions or sensors. Along with that, computers automatically adjust the timing of a vehicle, whereas in the past timing belts had to be adjusted manually.
Some cars feature additional computer components, such as cars that have anti-lock brake systems. Anti-lock brakes consist of the anti-lock brake control module, the computer, and the front and rear anti-lock brake sensors, which relay information to the control module, and the hydraulic control unit, or the HCU. Basically, the computer is checking all the time to make sure that your brakes aren't sliding. If the control modules sense that a wheel is going to lock, it shuts the normally-open solenoid valve for that circuit, which prevents any additional fluid from getting into that circuit.
There are also computer components for safety that sense collisions and deploy airbags, and still computers in some vehicles that sense rollovers, such as Sport Utility Vehicles, to tell how much weight is on one side or if the vehicle is swaying to one side. Other computers are strictly luxury based, and handle climate controls, GPS navigation, and keep track of favorite seat positions. Some use communications systems like On-Star, which are essentially are computer systems built into a car. Other computers take care of cruise control, keyless entry, security systems, and stereos. Even the automatic transmission is controlled by the car's computer.
Newer model cars feature up to 50 microprocessors, which are in every computer, that process the information coming in from the sensors. As technology improves, microprocessors become more common and more advanced, and they are capable of much more. Similar to desktop computers, almost every year microprocessors can do more than they could the year before.