# Fundamentals

#### Processes vs Threads

Main : Processes are executed by threads

#### Memory

**Stack**

- Stack allocation called by function
- Each function gets its own memory for local variables
- Freed immediately when function ends
- Too many function calls exceed stack capacity -> stack overflow error (JAVA) / **segmentation fault (CPP)**

**Heap**

- Manual deallocation required
- Accessible by multiple threads
- Heap is persistent until program termination
- **Memory leak :** allocated data is not freed after use

#### File I/O

#### Concurrency

#### Scheduling

#### System Calls

**Processes vs Threads**

- Process: own address space
- Thread: shared address space
- Context switching overhead
- When threads help vs hurt

**Memory**

- Stack vs heap
- Virtual memory
- Paging vs segmentation
- What a segmentation fault actually is
- Memory leaks and how they happen

**File I/O**

- File descriptors
- stdin/stdout/stderr
- Blocking vs non-blocking I/O

**Concurrency**

- Race conditions
- Mutex vs semaphore
- Deadlocks (4 conditions)

**Scheduling**

- Preemptive vs cooperative
- CPU-bound vs I/O-bound

**System calls**

- What they are
- Why they exist
- User mode vs kernel mode

### Practice explaining out loud

If she asks:

> “What happens when a program starts?”

You should mention:

- Executable loaded
- Virtual memory allocated
- Stack/heap setup
- Entry point (`main`)
- Syscalls for I/O