Hopfield model:

Fig: Hopfield model with four node

Distinguishing features:

1. Fully connected networks of neuron
2. Bi-directional connections
3. Symmetric weights {Wij=Wji}
4. Neurons are linear threshold elements
5. Asynchronous (most common) / Synchronous Operation
6. Computes by Energy Minimization (unlike error reduction as in Back Propagation)
7. Mostly used as Content Addressable Memory (CAM) and …