Pulses collected in flow cytometers are analog events
detected by analog devices
These pulses have a duration of no more than a few microseconds
If you cant digitize this pulse in that time you have
to deal with a combination of
analog and digital pulse processing
Until recently it took several microseconds to digitize
a pulse so this was not fast
enough for high speed collection
New systems which have all digital electronics can
digitize the pulse
directly at rates of several megahertz allowing all digital computation