2. Memory Layout: Stack, Heap, Code Segment, Registers, PC, File Descriptors, IPC

 High Address
    [ Stack ]          grows downward
    [ Heap ]            grows upward
    [ Data Segment ]    global/static vars
    [ Code Segment ]    your actual code
 Low Address

1. Stack — stores function calls, local variables, return addresses. LIFO, automatically managed (push on call, pop on return). Each thread has its own stack.

2. Heap — dynamic allocation, explicitly requested at runtime (malloc/free in C, new/delete in C++, garbage-collected in Java/Python). Shared across all threads of a process. Forgetting to free → memory leak.

3. Code (Text) Segment — compiled instructions, read-only, shared across threads.

4. Registers — tiny, ultra-fast CPU-internal storage (e.g., RAX for arithmetic results, RSP stack pointer, RBP base pointer). Each thread has its own set — saved/restored on context switch.

5. PC (Program Counter) — holds the address of the next instruction; increments after each instruction, updated on jumps/calls. Per-thread.

6. File Descriptors (FD) — integers representing open files/resources. 0→stdin, 1→stdout, 2→stderr. Shared across threads of the same process.

7. IPC — since processes have isolated memory, they need special mechanisms to talk: pipes, message queues, shared memory, sockets, signals, semaphores. Threads skip all this — they just read/write shared heap directly (with synchronization).

Concept Per Process Per Thread Where
Stack		One per thread	RAM
Heap	Shared		RAM
Code Segment	Shared		RAM
Registers		Per thread	CPU
PC		Per thread	CPU
File Descriptors	Shared		OS Kernel

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