Question

What is an activation record? What needs to be saved in it? (SML)

Answer 1

Active record is a data structure and it is an another name for the Stack Frame.
It stores the important state information for an instance of a function call. An active record can exist totally in memory or can be stored in the registers. Typically an Active record will store below information.
* Local variables of the callee fucntion
* Space for the return value of the fucntion
* Actual parameters to the fucntion
* A pointer to the Activation Record of the caller fucntion.

Generally Local variables and Actual parameters are cached in the registers. Activation Records follows the Last In First Out principle. Hence those are stored in a stack. This is the reason commonly Activation Records are called as Stack frames.