Most drivers do not know that a DUI is actually two separate charges.
Vehicle Code §23152(a) is the DUI charge that alleges the driver was operating a motor vehicle while impaired by alcohol or drugs. This would be the weaving, driving too slow, suspicious driving, etc.
Vehicle Code §23152(b), on the other hand, alleges that the driver was operating a motor vehicle with a blood alcohol content of 0.08% or more, regardless of whether there was suspicious driving or the driving was perfect.
Both charges are typically misdemeanors, and either charge alone will constitute a DUI.