1) Pure Aloha is a Continuous time system whereas Slotted Aloha
is discrete time system.
2) Pure ALOHA doesn't check whether the channel is busy before
transmission.
Slotted ALOHA send the data at the beginning of timeslot.
3) Pure aloha not divided in to time .Slotted aloha divided in
to time
4) In slotted ALOHA, a frame can be sent only at fixed times,
whereas in pure ALOHA, you can send any time.