Stack and heap are two memory regions used by computer programs to manage memory allocation, each with its own characteristics and purposes.

Stack Memory:

• Purpose: The stack is used for static memory allocation and stores variables that are declared and initialized in functions and methods. It is a region of memory that follows a Last-In-First-Out (LIFO) structure.
• Allocation: Memory on the stack is automatically allocated and deallocated as functions are called and return. When a function is called, space is allocated on the stack for local variables, function parameters, return addresses, and other bookkeeping information.
• Access: Access to stack memory is fast and efficient because it involves simple pointer manipulation. Local variables can be accessed directly by their memory addresses relative to the stack pointer.
• Size Limitations: The size of the stack is typically limited and fixed, defined by the operating system or runtime environment. Exceeding the stack size can lead to a stack overflow, causing program termination.
• Lifetime: Stack-allocated memory is short-lived and automatically freed when the function or scope in which it is allocated exits.

Heap Memory:

• Purpose: The heap is used for dynamic memory allocation and stores objects whose size is not known at compile time or needs to persist beyond the lifetime of the function or scope in which they are created.
• Allocation: Memory on the heap is allocated and deallocated explicitly by the programmer using memory management functions like malloc() and free() in languages like C, or by the language runtime environment in managed languages like Python and Java.
• Access: Access to heap memory involves indirect addressing through pointers. Memory allocation and deallocation may be slower than on the stack due to dynamic memory management overhead.
• Size Limitations: The size of the heap is typically larger than the stack and can grow dynamically as needed, subject to available system resources (e.g., physical memory, virtual memory).
• Lifetime: Heap-allocated memory can have a longer lifetime than stack-allocated memory, persisting until explicitly deallocated. Improper management of heap memory can lead to memory leaks, where allocated memory is not released after use, or to heap fragmentation, where memory becomes inefficiently fragmented over time.

In summary, stack memory is used for static memory allocation with a limited size and short-lived lifetime, primarily for managing function calls and local variables, while heap memory is used for dynamic memory allocation with a larger size and longer lifetime, primarily for managing objects and data structures that require flexibility and persistence.