Memory Fundamentals

Process Memory

Stack    ← Local variables, grows down
   ↓
Unused
   ↑
Heap     ← malloc lives here, grows up
BSS      ← Uninitialized globals
Data     ← Initialized globals
Text     ← Code

The Program Break

• Boundary between heap and unmapped memory
• sbrk(0) returns current break
• sbrk(n) extends heap by n bytes
• Returns (void*)-1 on failure, NOT NULL

Why Build Our Own Allocator?

sbrk alone cannot:

• Free memory in the middle
• Reuse freed memory
• Track allocation sizes

We need metadata and block management.