1. The stack is the memory set aside as scratch space for a thread of execution. When a function is called, a block is reserved on the top of the stack for local variables and some bookkeeping data.
  2. When that function returns, the block becomes unused and can be used the next time a function is called. The stack is always reserved in a LIFO (last in first out) order;
  3. the most recently reserved block is always the next block to be freed. This makes it really simple to keep track of the stack; freeing a block from the stack is nothing more than adjusting one pointer.


  1. The heap is memory set aside for dynamic allocation. Unlike the stack, there’s no enforced pattern to the allocation and deallocation of blocks from the heap;
  2. you can allocate a block at any time and free it at any time. This makes it much more complex to keep track of which parts of the heap are allocated or free at any given time
  3. There are many custom heap allocators available to tune heap performance for different usage patterns.

Each thread gets a stack, while there’s typically only one heap for the application

Which is faster – the stack or the heap? And why?
The stack is much faster than the heap. This is because of the way that memory is allocated on the stack. Allocating memory on the stack is as simple as moving the stack pointer up.

Where are the stack and heap stored?
Both stored in the computer’s RAM (Random Access Memory).

What is stored in stack and heap ?
Stack – Primitives, Calls to methods are stored on the stack
Heap – Class objects including method code and static fields in the heap space.

What determines the size of each of them?
The size of the stack is set when a thread is created. The size of the heap is set on application startup, but can grow as space is needed.

How do the stack and heap work in multithreading?
In a multi-threaded application, each thread will have its own stack. But, all the different threads will share the heap. Because the different threads share the heap in a multi-threaded application, this also means that there has to be some coordination between the threads so that they don’t try to access and manipulate the same piece(s) of memory in the heap at the same time.

How long does memory on the stack last versus memory on the heap?

Once a function call runs to completion, any data on the stack created specifically for that function call will automatically be deleted. Any data on the heap will remain there until it’s manually deleted by the programmer.

Can the stack grow in size? Can the heap grow in size?
The stack is set to a fixed size, and can not grow past it’s fixed size. So, if there is not enough room on the stack to handle the memory being assigned to it, a stack overflow occurs. This often happens when a lot of nested functions are being called, or if there is an infinite recursive call.

If the current size of the heap is too small to accommodate new memory, then more memory can be added to the heap by the operating system. This is one of the big differences between the heap and the stack.

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