Push Down Automata (PDA) is introduced and compared to finite state machines, highlighting its greater power and memory.

• PDA is introduced as a way to implement context-free grammars, similar to finite automata for regular grammars.
• The lecturer emphasizes that PDA is more powerful than FSM due to its additional memory in the form of a stack.
• It is clarified that PDA consists of a finite state machine plus a stack, which allows it to handle more complex languages that FSM cannot.

Stacks and their operations, push and pop, are explained as essential components of Push Down Automata.

• The concept of a stack is explained, emphasizing its usage in PDAs and its two main operations: push and pop.
• A stack is depicted as a collection of elements arranged vertically, with the topmost element being the focal point for operations.
• Push operation is adding a new element to the top, while pop operation involves removing the topmost element.

The lecture outlines the three primary components of a Push Down Automata: input tape, finite control unit, and stack.

• The lecturer identifies the input tape, finite control unit, and stack with infinite size as the three main components of a PDA.
• A diagram is provided to visualize these components, showing how the input tape feeds into the finite control unit, which interacts with the stack.
• The functionality of these components will be discussed in greater detail in future lectures.