I rather think that Hobbsy has scored a hole in one DB. The oscillator is the answer.
How does it work? Well in the same way as your spark changes from 6 volts to 20kv or more. You may want it technical but for the benefit of others I'll be as basic as possible. It's all to do with turns ratio of wire coils, and transfer of energy. When a magnetic field passes across a conductor [ copper wire ] it creates [ putting it very simply] a voltage in that wire, and the more turns of wire the more volts we get. Now we can also do it the other way around that is by passing an electrical current through a wire we will create a magnetic field around it. If we remove the supply from this wire then the magnetic field will collapse and if there is another wire beside it the collapsing field will pass across this wire and just as in the first example , induce a voltage into this wire. How are you doing DB, are you hanging in there. Now comes the clever bit.
If we use say 6volts for the wire that is going to be magnetised and hold it against a wire that is coiled into two turns, then when the 6volts is switched off there will be twice the voltage across these two turns. So now you have the expression Turns ratio under your bonnet it's all uphill from there. It follows then that the higher the ratio of turns , the higher the voltage will be in the second winding. Right now all we have two do is switch that voltage on the first wire on and off continuously so that we have a a continuous voltage on the second coil and that is done by a little bit of electronics called an oscillator. The proper name for these two windings are the primary and the secondary. They are wound in close proximity and then they are called a transformer for obvious reasons. In a CDI ignition this voltage is used to charge a capacitor to a high voltage as mentioned before, and this charge is switched very rapidly across the primary of another transformer called the ignition coil and the the whole process takes place again in that ignition coil. [Just another transformer] In INDUCTIVE DISCHARGE there is 6volts sitting on the primary winding and it is simply switched off...clean and simple.
Incidentally, the CDI oscillator also gives out RFI so keep it away from all receiver circuitry...wires etc.
I do hope this bit of bumf has been some help to you and yes I am British, although to be more precise ...English. I Really can't make out why when nationality is called for in most registrations we have got to select UK. The UK is not a country, it is a collection of countries..England Ireland Scotland and Wales and I feela little put out when I cannot state my country when every one else in the world can.
Sorry lads , rant over, Im off to bed night night.

db