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Intermediate Topic 33 of 51 Operating Systems

Memory Allocation

Strategies like first-fit and buddy systems.

How it works

Memory allocation gives programs blocks of memory on request. The stack allocates automatically in last-in first-out order, while the heap allows blocks of any size and lifetime through malloc and free or new and delete. Allocators use strategies such as first fit, best fit, worst fit, segregated free lists, buddy systems and slab allocation, trading speed against fragmentation. Modern allocators like jemalloc and tcmalloc use per-thread caches.

Step-by-step walkthrough

  1. A request for 25K arrives.
  2. First-fit takes the first block big enough, 100K.
  3. Best-fit takes the smallest sufficient block, 30K.
  4. Worst-fit takes the largest, 200K.
  5. Buddy systems split blocks in halves of power of two sizes.

Where it is used

Every dynamic data structure relies on allocation, and kernels use slab allocators for fixed-size objects. Garbage-collected languages build collectors on top of heap allocators.

Common pitfall

Memory leaks, double frees, use-after-free and buffer overflows are the main bugs in manual management. External fragmentation leaves unusable gaps, while internal fragmentation wastes part of blocks. Allocation can be slow under lock contention. Use tools such as Valgrind and AddressSanitizer, prefer arenas for many short-lived objects and avoid frequent small allocations.

Where it fits in the course

Memory Allocation is topic 33 of 51 in Operating Systems, rated Intermediate. It follows Thrashing. The next topic is Memory Mapped Files.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Operating Systems quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Memory Allocation?
Strategies like first-fit and buddy systems. It belongs to Operating Systems and is an intermediate-level topic.
Where do people use Memory Allocation?
Every dynamic data structure relies on allocation, and kernels use slab allocators for fixed-size objects.
What is the most common mistake with Memory Allocation?
Memory leaks, double frees, use-after-free and buffer overflows are the main bugs in manual management.
What should I learn before this topic?
Start with Thrashing, the topic just before it in Operating Systems.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Operating Systems quiz.
Is Memory Allocation hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Memory Allocation?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Memory Allocation?
Thrashing, Memory Mapped Files, Page Replacement Algorithms are closely connected. The full list is in the related topics section of this page.
What should I study after Memory Allocation?
Continue with Memory Mapped Files, the next topic in Operating Systems.

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