With slotted Aloha a terminal can only transmit at the beginning of a fixed sized slot. Transmitting in fixed time slots reduces the probability of collision. Frames cannot partially overlap. As the load on the network increase, that is the number of frames transmitted every second increases, the throughput or number of successful transmissions per second increases at first. As the network gets busier, the throughput starts to decline until very little data is successfully received when the network is very busy.
Ethernet is similar to Aloha networks.
If another station is currently transmitting, it waits until that transmission is complete. This produces better throughput than Aloha because it tries to avoid collisions. If two stations start transmitting at exactly the same time, a collision will still occur. When a collision occurs, both stations will wait a random amount of time and then try again. If one stations starts to transmit, the other station will not see the transmission until it travels down the wire from the other station.