Programmed Fuel Injection, or PGMFI/PGM-FI, is the name given by  Honda to a proprietary digital electronic fuel injection system for internal combustion engines which injects the right amount of fuel per cylinder based on specific engine data, available since the late 1980s. This system has been implemented on motorcycle and automobiles. 

The PGM-FI is one of the core technologies to attain the goals of clean exhaust gas and fuel economy. An inevitable next goal is to extend the application of the innovative technique to models in various categories that respond to a larger number of users. Through the newly developed compact PGM-FI, Honda increases the application from large touring models, to the super sport models, and the models targeted towards a larger number of people.

The Engine Control Unit (ECU) has sensors which measure the temperatures of the engine, coolant, oil, and outside air as well as pressure sensors to monitor oil and barometric pressure. Based on these readings and the location of the throttle, the ECU calculates how much oxygen and fuel should be mixed for optimal and efficient performance.

With the move from carburetors to fuel injection, computers have assumed an important role in the proper functioning of an engine. The level of precise control possible with a ECU  (Engine Control Unit - computer for running an engine) can not only allow for greatly improved fuel economy, but can also allow for fine tuning of an engine to a degree that is arguably impossible with the best carburetors. Many ECUs, including those made by Honda, do data interpolation, allowing them to intelligently compensate for engine conditions that fall "between" known states, allowing for an almost continuously variable response to varying engine conditions. Additionally, the ECUcan make small corrections to fuel/timing based on the state of various engine sensors. It is probably fairly fair to say that from the factory, most manufacturers tune for fuel economy, emissions and poor quality gasoline as opposed to power and race gas.

Beware of most aftermarket "chips": more often than not these programs just dump more fuel and increase timing greatly while doing things like raising revlimiters far beyond safe levels. There are very limited gains to be had from most "performance chips." Tuning not "chipping" generally produces usable, real world gains. That being said, changing the program of a ECU is generally not that tricky. First, it would probably be wise to focus on some basics of how ECUs work so that it is more apparent where we could makes changes to have a positive effect on performance.