A "channel" is just a named property (name can be anything) that you can put a value into. Then you can recall that value later by selecting that channel, where applicable. So if you think of a particle as a collection of properties (position, scale, velocity, shape, etc)...custom data channels are just extra pieces of information attached to particles, that you can name for easy reference later. Float channels contain single numerical values, Vector channels contain 3 floats and TM channels contain a full 4x3 transform (12 floats).
"Targets" are referenced throughout the UI, but they're really no different than any other custom (float) data channel. The key takeaway about targets is that the data they contain is specifically the ID of other particles in the system. But ultimately a "target" channel is the same as any other float channel...it's just a channel (with an arbitrary name, although "target" is the suggested one) that contains a float value.
You can't delete channels, but there's not really ever a need to. You can "invalidate" a target channel by setting the value to -1. All particle IDs are >= 0 so a particle ID will never be less than 0.
For particle counts, you can view them either in the MAXScript listener, where they're printed by default, or right click in the editor and choose the particle count display option.
"Targets" are referenced throughout the UI, but they're really no different than any other custom (float) data channel. The key takeaway about targets is that the data they contain is specifically the ID of other particles in the system. But ultimately a "target" channel is the same as any other float channel...it's just a channel (with an arbitrary name, although "target" is the suggested one) that contains a float value.
You can't delete channels, but there's not really ever a need to. You can "invalidate" a target channel by setting the value to -1. All particle IDs are >= 0 so a particle ID will never be less than 0.
For particle counts, you can view them either in the MAXScript listener, where they're printed by default, or right click in the editor and choose the particle count display option.