OS 101

Definition: A program that acts as an intermediary between the user and the computer hardware.
- Goals of Operating Systems:
  - Execute user programs and make solving user problems easier.
  - Make the computer system convenient to use.
  - Use the computer hardware efficiently.

Purposes:
- Controls allocation and use of the computing system's resources among various users and tasks.
- Provides an interface between computer hardware and programmer for coding and debugging of application programs.
Tasks:
1. Provides facilities to create and modify programs and data files using an editor.
2. Access to the compiler for translating the user program from high-level language to machine language.
3. Provides a loader program to move the compiled program code to the computer's memory for execution.
4. Provides routines that handle the details of I/O programming.

Components of Computer System:
1. Hardware: Basic computing resources including CPU, memory, and I/O devices.
2. Operating System: Controls and coordinates the use of hardware among various applications and users.
3. Application Programs: Define the ways in which system resources are used to solve computing problems (e.g., word processors, compilers, databases).
4. Users: Include people, machines, and other computers.
Abstract View of Components:
- User → Application Programs → Operating System → Computer Hardware

Main Memory:
- The only large storage media that the CPU can access directly.
- Typically volatile and random access memory (e.g., DRAM).
Secondary Storage:
- Extension of main memory providing large, non-volatile storage capacity.
- Hard Disk Drives (HDD):
  - Made of rigid platters covered with magnetic material, divided into tracks and sectors. Disk controllers manage interactions between computer and device.
- Non-volatile Memory (NVM): Faster than hard disks and non-volatile. Becoming popular due to improvements in capacity and performance.

Storage systems are organized in a hierarchy based on speed, cost, and volatility.
Caching:
- Copies information into a faster storage system; main memory serves as a cache for secondary storage.
Device Driver:
- For each device controller to manage I/O, providing a uniform interface between the controller and kernel.

OS provides an environment for program execution and services for programs and users:
- User-Focused Services:
  - User interface, program execution, I/O operations, file-system manipulation, communications, error detection.

Efficient Operation Services:
- Resource allocation, logging, protection, and security.

Elements:
- Icons, buttons, menus, windows, pointers.
System Calls:
- Programmatic way for computer programs to request services from the OS kernel. They provide the operating system's services to user programs via the Application Programming Interface (API).

File System Operations: Create, delete, and manipulate files.
Process Control: Manage processes including creation, termination, allocation, and deallocation.
Memory Management: Handle memory allocation, deallocation, and dynamic resizing.
Interprocess Communication (IPC): Handle communication between processes.
Device Management: Interact with peripheral devices.

System Programs: Provide a convenient environment for program development and execution.
- File Manipulation: Creating, deleting, and managing files and directories.
- Status Information: Information retrieval from the system like date, time, and resource availability.

File Modification: Using text editors and commands to modify files.
Programming Language Support: Provide compilers and interpreters.
Communications: Mechanisms for virtual connections among processes and users.
- Background services are launched at boot time and responsible for system management.
- Application programs generally do not pertain to system functions.

User Interface: Includes GUI and command line.
Services include program execution, I/O operations, communication systems, resource allocation, error detection, and hardware management.

Process: A program in execution, managed by the OS for efficiency.
- Comprises different sections: text (code), stack (temporary data), data (global variables), heap (dynamically allocated memory).
Process vs. Program: Programs are passive entities stored on disk; processes are active in memory. Multiple processes can exist for one program.

States of a Process:
- New, Running, Waiting, Ready, Terminated.
Process Control Block (PCB): Holds information on process state, program counter, memory limits, and I/O status.

Process Creation: Parent processes create child processes forming a tree structure and are managed by process identifiers (pid).
Process Termination: Managed using exit() system call; can terminate child processes during execution.

Processes can be independent or cooperating, with reasons for cooperation including information sharing and computation speedup.
Two IPC models: Shared memory and message passing.

Thread: Basic unit of CPU utilization consisting of an ID, program counter, register set, and stack, sharing resources with other threads in the same process.
Traditional processes have a single thread, while multithreaded processes can perform multiple tasks simultaneously.

Concurrency: Multiple processes making progress over time; Parallelism: Multiple tasks performed simultaneously.
Types of parallelism: Data parallelism and task parallelism.

Maximum CPU utilization is achieved through multiprogramming. CPU bursts and I/O wait times influence performance.

Allocates CPU cores to processes in the ready queue under various circumstances. Preemptive and non-preemptive scheduling types exist.

Goals include maximizing CPU utilization and throughput while minimizing turnaround, waiting, and response time. Convoy effect can occur in scheduling.

Shortest-Job First (SJF): Minimizes average waiting time, can be preemptive.
Round Robin (RR): Allocates small time slices for process execution, ensuring fairness.
Priority Scheduling: Assigns priorities to processes, with potential starvation and aging addressed.