Is there a difference between barbiturates and benzodiazepines?

Barbiturates/ benzos: The biggest difference between barbiturate and and a benzodiazepine is the fact that the barbiturates lead to a much more rapid habituation and the withdrawal can be very serious and they can be lethal at low doses. Benzodiazepines have all the same risks except that they are far less likely to be lethal and tolerance does not develop that quickly and in many patients not at all.

Yes, very different: Barbiturates are sedatives with a low "therapeutic index", meaning that a toxic dose isn't much higher than an effective dose. Benzodiazepines are tranquilizers (some sedating, some not) with a higher therapeutic index, i.e., safer. Chemically they are completely different. However, both can be addictive, with tolerance developing with repeated doses.