blow off valve vs. diverter valve

can some one please explain the differences between a blow-off valve and a diverter valve. Also, why do I need a wastegate when I have a BOV or DV?  

BOVs and DVs serve the same purpose, they vent excess boost from the intake tract. The difference being that a BOV vents the extra boost pressure out into the atmosphere so you are loosing that boost, a diverter valve however blows the extra boost back into the intake before the turbo so it is used to keep the turbo spinning reducing lag. Some people will argue that you don't want the boost recirculating because it is blowing hot air back into the turbo and you want cool air from the outside. Most cars that originaly were equiped with a diverter valve seem to perform better when you stay with the diverter valve. It seems most peoples argument for a BOV is they like the noise it makes.

A wastegate is similar to a BOV or DV except it is between teh exhaust manifold and the turbo. It opens to allow exhaust gasses to bypass the turbo. it does this to keep the turbo from spinning beyond its intended RPM maximum.