Basics of operating systems

Operating system

An operating system is software that manages the computer’s hardware and software resources and provides services for application programs.

Kernel vs kernel space

Kernel

• The kernel is the core part of an operating system.
• It is the software component that manages hardware resources (cpu, memory, devices)
• It provides services to user programs.
• Tasks : process scheduling, memory management, device control, and system calls.

Kernel space

• Kernel space is the protected memory area where the kernel code executes.
• User applications cannot directly access kernel space for safety and security.

OS structure

• The term “os structure” refers to the organization and design of an operating system (os).
• It describes how the various components of an os are arranged and interact to manage hardware and provide services to users and applications.

Monolithic structure

• Entire os runs as one large program in kernel space.
• All services (file system, device drivers, memory management) are part of a single block of Code.
• Pros:fast and efficient
• Cons: hard to maintain and less secure

Layered approach

• Os divided into layers; each layer provides services to the layer above.
• Example: hardware→ device drivers→ file system → user interface
• Pros: easier to debug and maintain
• Cons: performance overhead due to layers

Microkernel structure

• Kernel provides only essential services (e.g., communication, basic i/o).
• Other services run in user space as separate processes.
• Pros: more secure and stable; easy to extend
• Cons: may be slower due to more context switches

Modular structure

• Os is divided into modules that can be loaded or unloaded dynamically.
• Like a hybrid of monolithic and microkernel approaches.
• Pros:flexibility and easier updates

Operations & services

• Operations of an operating system manages the computer hardware and provides a platform for applications to run
• Services of operating systems provide a variety of services to users and applications

Operations

• Process management : manages program execution and cpu scheduling.
• Memory management : controls allocation and deallocation of ram.
• File system management : organizes data on storage devices (hdd, ssd).
• Device management : uses device drivers to communicate with hardware devices and applications.
• Security & access control: protects data and resources from unauthorized access.
• Networking : manages network connections and communication protocols.

Services

• user interface (ui) : command-line interface (cli) or graphical user interface (gui) for interacting with the system.
• program execution : loads and executes programs.
• i/o operations : provides abstractions for input/output devices.

System calls

Definition

• It is a interface between user programs and the os.
• It allows programs to request services from the os.
• Examples
  • fork( ) – create a new process
  • exec( ) – run a new program
  • read( ) – read data from a file
  • write( ) – write data to a file

Operating system

Design goals

• Operating systems are designed with multiple objectives in mind
• Efficiency : the os should use system resources (cpu, memory, i/o) optimally and provide fast response times.
• Reliability : the os must run stably and recover gracefully from errors
• Portability : the os should run on different hardware platforms without major redesign.

Implementation

• Choice of programming language : c/c++ are commonly used because they allow low-level memory and hardware access & portable across multiple architectures
• Kernel structure : the kernel is the core of the os and implements the most critical operations
• Modular design : os is broken into modules for easier maintenance and scalability
• Hardware abstraction : the os uses a hardware abstraction layer to interact with different hardware without changing the kernel code.

System boot

• When you turn on a computer, the bootstrap loader (a small program in rom) loads the os kernelinto memory.
• After this, the os takes control of the system and starts managing resources.