Stack and Heap in Programming: Memory Location

Стек и куча are the two primary regions of a program’s memory: стек памяти (the call stack) holds function frames, local variables and return addresses, while куча памяти (the heap) stores objects and buffers allocated at runtime. The stack is LIFO and managed by the compiler/CPU (fast, short-lived); the heap is managed by the language runtime or OS allocator (flexible but slower and subject to fragmentation). Both live in the process’s virtual address space and are mapped onto physical RAM (and swap) by the operating system.

Contents

• What are the stack and heap? (стек и куча)
• Where are they physically located in memory?
• OS vs language runtime: who controls what?
• Scope and lifetime of stack and heap
• What determines stack and heap sizes (стек памяти и куча памяти)?
• Why is the stack usually faster than the heap?
• Sources
• Conclusion

What are the stack and heap? (стек и куча)

At a high level: the stack is the program region used for function call bookkeeping — activation records or stack frames that contain return addresses, function parameters and local (automatic) variables. The heap is the region used for dynamic allocations: objects, buffers and data whose lifetime you control with allocation APIs (malloc/free, new/delete) or whose lifetime is managed by a garbage collector in managed languages. See a compact community explanation on the call stack and heap at Stack Overflow.

Key practical differences

• Allocation/deallocation: stack allocation/deallocation is automatic (entry/exit of functions); heap allocation is explicit (or handled by GC).
• Lifetime: stack items live while a function is active; heap items live until freed or collected.
• Ownership and visibility: stack is private to the thread that owns it; the heap is shared across threads in the same process (synchronization needed).

Tiny C example (illustrates where values go):

void example() {
 int a = 5; // 'a' lives on the stack
 int *p = malloc(sizeof(int)); // '*p' points to memory on the heap
 *p = 10;
 free(p);
}

Danger: returning a pointer to a local (stack) variable yields a dangling pointer:

int* bad() {
 int x = 42;
 return &x; // undefined behavior — x is on the stack and will be gone
}

For deeper comparisons and allocation details see the explanatory articles on Educative and GeeksforGeeks.

Where are they physically located in memory?

Programs run in a virtual address space provided by the OS. The stack and heap are regions inside that virtual space — not fixed physical addresses you can directly control. Typical layout (simplified):

• low addresses → code/text segment (program instructions)
• data segment (.data/.bss) → global/static variables
• heap → grows upward as allocations occur
• unused address gap
• stack → starts near high addresses and often grows downward

So where do those bytes actually live physically? The OS (with the MMU) maps virtual pages to physical RAM pages. Pages can be backed by RAM, and if the system is under memory pressure they can be swapped out to disk. The mapping means “where in physical RAM” can change over time and is invisible to normal programs. For an accessible overview of the virtual layout and OS mapping, see Baeldung and the Educative comparison of stack and heap behavior in virtual memory Educative.

Two practical points:

• Each thread gets its own stack region (separate stacks per thread).
• The heap is (generally) a shared area for the whole process; the allocator requests pages from the kernel (e.g., via brk/sbrk or mmap on Unix-like systems).

OS vs language runtime: who controls what?

Control is split across several layers.

Operating system responsibilities

• The OS creates the process address space and maps pages into it. It sets default stack size limits, enforces page protections, and services system calls used to grow/commit memory. The OS also swaps pages to disk when needed.
• The OS usually provides low-level primitives for changing a process’s heap (brk/sbrk, mmap) and for creating threads with a stack size parameter.

Language runtime / allocator responsibilities

• The language runtime or C library implements the heap allocator (glibc malloc, ptmalloc, jemalloc, tcmalloc, etc.). These allocators manage free lists, arenas and metadata, and they decide when to ask the OS for more memory. See the practical allocator discussion at GeeksforGeeks and the runtime view at Educative.
• Managed runtimes (JVM, CLR) implement their own heaps and garbage collectors. They may reserve large virtual regions and control when memory is committed or compacted; they expose configuration (for example JVM’s -Xms/-Xmx) to limit or tune heap behavior.
• The compiler generates code that adjusts the stack pointer to allocate a stack frame when a function runs; the CPU executes these instructions directly.

In short: the OS provides the address space and low-level services; the runtime and libraries implement higher-level allocation policies and bookkeeping. You can’t directly address physical memory from user code; you interact with virtual memory and APIs.

Scope and lifetime of stack and heap

Scope (visibility)

• Stack variables are scoped to the function/block that declares them. You can’t rely on them after the function returns.
• Heap allocations have no implicit scope; they remain reachable across function calls and threads for as long as references to them exist (or until the runtime/GC frees them).

Lifetime (how long the data lives)

• Stack: lifetime == function activation. Short and deterministic. No manual free needed.
• Heap: lifetime is dynamic. In manual-management languages (C/C++) you free memory with free/delete; in managed languages the garbage collector reclaims unreachable objects.

Threading note: because each thread has its own stack, local variables are naturally thread-local; heap objects are shared and therefore may need locks or atomic operations when accessed concurrently.

Practical hygiene tips

• Don’t return pointers to stack memory.
• Free or release heap memory you own (or prefer RAII/smart pointers in C++).
• In managed languages, avoid keeping unnecessary references to large heap objects if you want them to be collectible.

What determines stack and heap sizes (стек памяти и куча памяти)?

Stack size

• Default stack size is set by the OS and by the way a program or thread is created. For example, many systems use platform defaults (examples cited in educational references: e.g., ~1 MB on some Linux setups and ~8 MB on Windows — defaults vary by distro and toolchain) — see Educative.
• You can change stack size via OS or runtime tools: shell limits (ulimit -s on Unix), thread creation attributes (pthread_attr_setstacksize), or linker/IDE settings when building an executable. Embedded systems may set a fixed, small stack.
• Stack overflow happens when you exceed the reserved stack (deep recursion, very large local arrays).

Heap size

• Heap capacity is governed by the runtime and the OS. Allocators typically request more virtual memory from the kernel as needed (using brk/sbrk or mmap on Unix). The process is limited by available virtual address space, physical RAM, and OS-enforced limits (ulimit -v, cgroups on Linux, or system-level resource limits). Managed runtimes often expose explicit configuration (for example JVM flags) to set minimum and maximum heap sizes.
• Fragmentation and allocator policy can make the usable heap smaller than the total virtual region.

Reserved vs committed memory: modern allocators sometimes reserve a large virtual address range but only commit physical pages when the memory is actually used; that helps avoid immediate large physical RAM consumption.

If you need to tune limits: check platform docs and runtime settings. The allocator and OS together determine how much memory a process can actually get.

Why is the stack usually faster than the heap?

Short answer: simplicity and locality.

Reasons the stack tends to be faster

• Allocation/deallocation cost: stack uses simple pointer arithmetic (adjust the stack pointer); it’s essentially constant-time. Heap allocators must search free lists, split/merge blocks, maintain metadata and sometimes acquire locks — all costlier operations.
• Contiguity and cache locality: stack frames are allocated in a contiguous region as functions are called; that improves CPU cache behavior and prefetching. Heap allocations can be scattered, which increases cache misses.
• No synchronization: the stack belongs to a single thread, so you don’t pay synchronization costs. The heap is shared and many allocators need to guard data structures against concurrent access (though modern allocators reduce contention using per-thread arenas).

But performance depends on access pattern too. If you allocate a large, contiguous buffer on the heap and access it sequentially, it can be extremely cache-friendly and fast. Conversely, many tiny heap allocations that produce pointer-chasing patterns will be slow. Modern allocators and garbage collectors (in managed runtimes) use techniques like pooling, compaction and thread-local arenas to reduce the overhead and fragmentation — so heap performance can be very good in practice. For a clear exposition of these trade-offs, see Educative and GeeksforGeeks.

Practical rule of thumb: use the stack for small, short-lived data; use the heap for large or long-lived data and shared objects. And measure — profiles often reveal surprising bottlenecks.

Sources

• What and where are the stack and heap? — Stack Overflow
• Stack vs Heap: What’s the difference? — Educative
• Stack vs Heap Memory Allocation — GeeksforGeeks
• What and Where Are the Memory Stack and Heap? — Baeldung
• Основные принципы программирования: стек и куча — tproger
• Стек и куча в C++ / Ravesli

Conclusion

In short: стек и куча describe two complementary memory regions inside a process’s virtual address space — стек памяти for short-lived, automatically managed activation frames; куча памяти for dynamic, flexible allocations managed by the runtime or programmer. The OS provides the virtual address space and enforces limits; the runtime and allocator implement policies for growth, fragmentation management and garbage collection. Want predictable speed and lifetime? Use the stack. Need flexibility and shared objects? Use the heap — but watch your limits, fragmentation and synchronization.