If your car is less than a decade old, you can hook into a wealth of real-time information through its on-board diagnostic port.
If you say "car computer," most auto repair shops will assume you mean one of the various electronic control units, or ECUs, built into your car. Almost all modern vehicles are computerized in the sense that they have computers that read inputs from various sensors and use that information to control the engine, transmission, and other electronic systems. Most car users are not even aware of the existence of these computers (until they break, at which point they become very aware of the expense of replacing them). However, people who modify their cars with aftermarket performance parts sometimes need to provide new software to the computers in order to take maximum advantage of the new hardware they've installed. This process, known as chipping, is often as simple as replacing a single EEPROM (Electrically Erasable and Programmable Read-Only Memory) chip.
ECUs are not monolithic computers that control everything in your car. In fact, cars have many different ECUs, such as the Electronic Control Module (ECM), which controls smog emissions through engine tuning; the Powertrain Control Module (PCM), which controls the transmission and engine; and the Vehicle Control Module (VCM), which oversees a number of non-smog-related functions, including antilock braking systems.
Almost all new consumer vehicles conform ...