For the non-electronics engineer, here is an explanation of how the CB650 CDI works.
Take a look at the Honda shop manual, section 17, page 200 for the schematic of the amplifiers (which are also used on several other branded bikes of the era). You will see where Honda points out "CONDENSOR PULSER GENERATOR", which is a capacitor that is held at 1/2 Vcc (about 6 volts here). This capacitor shapes the pulse from the coil on the spark pickup that is mounted to the engine.
When the trigger pulse arrives from the coil it discharges this CONDENSOR PULSER GENERATOR to 0 volts for a single pulse discharge. This pulse is limited to 0 volts (actually -0.6 volts) by the DIODE, as labeled to protect TRANSISTOR1 from too much reverse-bias (which would damage it). This causes the collector of TRANSISTOR1 to spike to 12 volts for the same pulse duration, which is current-boosted by TRANSISTOR2 to drive the power output TRANSISTOR3. This final transistor powerfully pulses the very low-ohms IGNITION COIL to make a spark. (It is a pulse-drive system, not a Kettering coil-discharge arrangement.) The negative kickback voltage form the primary side of the coil, which would normally overly reverse-bias TRANSISTOR3 and damage it, is limited to 0.6 volts by the ZENER DIODE, while the peak voltage kickback of the coil is limited by this ZENER DIODE to a safe level that won't hurt the power transistor. (Note: this is why, when riders change to "high output" coils on this system, it eats the power transistor: too much kickback voltage from such coils overloads this ZENER DIODE and shorts it out).
This is the classic Capacitive Discharge Ignition system, as designed in the early 1960s, and several times published for builders (like me) in places like Electronics Design Magazine, Popular Electronics, Hotrod magazine, and many other places. The spark duration is controlled by the DISCHARGE of a CAPACITOR, hence the name. The capacitor's storage (in uF) determines how long the coil will be pulsed.
In the late 1960s and through the 1980s there were (large and expensive) aftermarket CDI boxes made that multiplied the 12 volts of a typical car to be several thousand volts, using oscillator circuits and transformers, to supply this high voltage to the coils' primary side, thus multiplying the output side of the coil to dozens, even hundreds, of thousands of volts. This was needed then to fire nitro-fueled engines: the large storage of this high voltage was done using a bank of high-voltage capacitors to store enough energy to ensure the spark would happen, because if one of these engines misses one sparkplug firing, the engine will self-destruct due to the fuel being liquid and fully compressed when the spark fires. So, there had to be NO CHANCE of a misfire, and these fancy high-power ignitions ensured the spark would happen, even if the sparkplug came apart for some reason. Since these racing versions were also capacitive-discharge-signal driven (like the CB650 version), they were called Capacitive Discharge Ignitions. The marketers of the MSD version never bothered to explain that they didn't invent it: they just claimed to be the best at it, and advertised like they were the only inventors of it. So, this is what most folks think of when they now hear the term "CDI", but that's not the truth: there are many simpler versions of them out there - including the ones used in the CB650. Since around the 1990s there have been those (probably lawyers for MSD) who decided to call the ones without thousands of volts of coil drive energy "pulser ignitions" instead, but they aren't - and now, you know the difference.
