What is a memory stack ? Explain its role in managing subroutines with the help of neat diagrams.

What is a Memory Stack?

Think of a memory stack like a stack of trays in a cafeteria. When you need a tray, you take one from the top of the stack. When you’re done with it, you put it back on top. Similarly, a memory stack is a structure used by a computer to keep track of the current state of programs as they run.

Role in Managing Subroutines:

1. Supporting Program Execution: The stack helps keep track of where the program is and what it needs to do next.
2. Returning Control: When a program calls a subroutine (like a function), it needs to remember where it left off once the subroutine finishes. The stack helps by storing return addresses.
3. Storing Return Addresses: As the program calls subroutines, the addresses of the instructions to return to are pushed onto the stack. This ensures the program knows where to go back to.
4. Dynamic Nesting: The stack can handle multiple levels of subroutine calls (nested calls) within memory limits.

1. Storing Subroutine Information: Besides return addresses, the stack also holds other important information like subroutine arguments and local variables.
2. Using Frames: Each time a subroutine is called, the information related to that call, including return addresses and variables, is stored in a “frame” on the stack.
3. Keeping Track of Execution State: The stack reflects the current state of the program as it executes, making it easier to manage and debug.
4. Managing Pointers: Special pointers, like the frame pointer, help keep track of different parts of the stack, making it easier for the program to find what it needs.

Diagram Explanation:

Imagine you’re at a cafeteria:

• Unallocated Stack Frame for b(): This is like an empty tray waiting for someone to use it.
• Stack Frame for a(): This tray holds information about the function “a()” while it’s running.
• Stack Frame for main(): This is the tray for the main program.
• Low Memory to High Memory: Just like trays are stacked from bottom to top, memory addresses are organized from low to high.

When a subroutine is called, it’s like picking up a new tray (stack frame) from the stack. When the subroutine finishes, its tray is removed, and you go back to using the previous tray (returning to the main program or another subroutine).