OS Functions
- Memory management: Allocates and deallocates RAM to processes. Enforces process isolation via virtual memory.
- File system management: Organises how files are stored, named, and retrieved on storage. Manages permissions
- Device management: Translates OS commands into hardware-specific signals via device drivers.Handles hardware interrupts.
- Scheduling: Decides which process gets CPU time, for how long, and in what order. Covered in A1.3.3.
- Security: Manages user/group permissions (ACLs), encryption, firewalls, antivirus
- Accounting: Records how much CPU time, memory, disk I/O, and bandwidth each process uses. Used for billing in cloud environments, performance monitoring.
- GUI: graphical user interface
- Virtualisation: Runs multiple virtual machines (VMs) on one physical machine. Each VM is isolated from others.
- Network management: Manages the network stack : protocols, connections, bandwidth allocation, and configuration.Packet transmission via the NIC.
Process Detail
- Thread: Smallest unit of execution within a process. Threads share memory space. Multi-threaded processes can run tasks in parallel on multi-core CPUs.
- Sandboxing: Isolates a process to only the resources it strictly needs. Limits damage from bugs or malicious code.
- User mode vs kernel mode: Applications run in user mode and cannot directly access hardware. The OS kernel runs in kernel mode with full hardware access. This separation protects the OS from faulty or malicious applications.
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