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copied!<p>First, a small clarification. Stacks are not necessarily in DRAM. they are just a structure that can be formed in any memory: DRAM, caches, disk. </p> <p>To understand a stack, you should first understand what is a stack. It is like a stack of trays, the properties that make it a stack are: </p> <ul> <li>You can only access the top element of the stack</li> <li>It is Last In First Out, i.e., when you go to get a data from a stack you get the data that was stored last on the stack. </li> </ul> <p>The act of storing something in a stack is called PUSH and removing it is called a POP. Say I do the following to an empty stack: </p> <pre> PUSH A PUSH B PUSH C </pre> <p>Then the stack will contain </p> <pre> C - Top B A </pre> <p>Now if I execute a POP (notice there is no operand here), it will return C and the stack will contain</p> <pre> B -- top of stack A </pre> <p>So stack in processors is just a hardware implementation of the above algorithm. </p> <p>A register contains the address of the top of stack called <i> stack point </i> The ISA (Instruction Set Architecture) provides PUSH and POP instructions to access the stack variables as I showed above. </p> <p>This is a very useful construct. A stack is used to store local variables, basically temporary data that you want to remove at the end of a function call. It specifically helps with function calls. When a function is called, the variables of the newly called function's local variables are pushed on the stack. </p> <pre><code>foo(){ int a; int b; // both registers containing a and b are PUSHed here on the stack c = bar(); // pop the stack to get value of c print c } bar(){ int z; // local variables pushed on top of the stack z = ... return z; // pop all local variables of bar(), then push z on the stack } </code></pre> <p>I hope the above helps. </p>

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