On the top of the engine is a large red plate. Underneath it contains 4 coils packs that sit over the spark plugs. That means that each spark plug has its own spark generated very close and removes the need for ignition leads and associated problems.
The unit is a single removable item (you get the wholed red plate and associated gubbins together)and usually lasts about 100k miles, costs about 150gbp to replace.
PS - DI = Direct Ignition and its usually called the DI Cassette.
some thing intersting the DI ignition.once the ignition is turnt off the DI system remains on for 6 sec then the trionic control module earths all the trigger leads 210 times second in order to burn off impurities from the spark plug electrodes