Operating System: Intro and Architecture

Introduction

• The operating system (OS) is a program that manages a computer's hardware resources.
• The OS acts as an intermediary between the user and the computer hardware.
• Mainframe, personal computer (PC), and mobile are types of operating systems.

Computer System Architecture

• Hardware provides basic computing resources, including the CPU, memory, storage, and I/O devices.
• The operating system controls and coordinates the use of hardware among various applications and users.
• Application programs solve computing problems for users, e.g. word processors, email, web browsers, video games, media players.
• Users can be people, machines, or other computers.

OS: User View

• Users prioritize convenience, ease of use, and good performance.
• Users typically do not focus on resource utilization.
• Shared computers must keep all users happy.
• Workstations have dedicated resources but also use shared resources from servers
• Handheld computers are resource-constrained and optimized for usability and battery life.
• Some computers, like those in devices and automobiles, use embedded systems that may have limited interfaces.

OS: System View

• The OS is a resource allocator that manages resources and resolves conflicting requests.
• The OS is also a control program that controls the execution of user programs.
• It also prevents errors and improper use of the computer system.

Defining the OS

• An operating system is defined as everything a vendor ships when an operating system is ordered.
• The OS is also defined as "the one program running at all times on the computer"

OS vs Kernel

• Key components include the kernel, device drivers, utilities, system libraries, and a user interface.
• The kernel performs memory management, disk management, process management and task management.

Computer System Operation

• The computer system operation involves one or more CPUs and device controllers connected through a common bus.
• The bus provides access to shared memory for the CPUs and device controllers
• CPUs and devices can execute concurrently, competing for memory cycles.

Device Controllers

• Device controllers contain local buffer storage and special-purpose registers.
• I/O devices and the CPU can execute concurrently.
• They moves data between devices and local buffers
• The device controller informs the CPU that it has finished its operation through an interrupt

Device Drivers

• Operating systems use device drivers for each device controller.
• Device drivers understand the device controller.
• Device drivers provides the rest of the OS with a uniform interface to the device.

Interrupt Handling

• Interrupt Vector Table (IVT) contains pointers that contain addresses of all the service routines.
• During interrupt handling, the contents of CPU registers and the program counter (PC) are saved on the system stack.

Storage Structure

• The levels of storage from fastest to slowest are registers, cache, main memory, solid-state disk, hard disk, optical disk, and magnetic tapes.

Operating System Operations

• Dual-Mode operation allows the OS to protect itself and users.
• This is done through User Mode and Kernel/Supervisor/System/Privileged Mode
• The Mode bit is provided by hardware
• Mode bit is a hardware feature to differentiate between user code and kernel code execution.
• Privileged instructions can only be executed in kernel mode.
• A system call changes the mode from user to kernel, and returning from the call resets it to user mode.
• During boot time, hardware starts in kernel mode.
• After the OS is loaded, user applications start in user mode.
• When a trap or interrupt occurs, hardware automatically switches from user mode to kernel mode.
• Examples of privileged instructions are I/O control, timer management, and interrupt management.

Computing Environments

• Computing environments include multiprocessor systems
• Computing environments can also be multicore systems
• Multi-core systems have dual cores in the same chip

Multiprogramming (Batch System)

• A job pool contains processes on secondary storage awaiting to be brought into main memory. -Main memory consists of OS, Job P1, and Job P2
• While Job P1 performs I/O, Job P2 can be executed by the CPU.

Multitasking

• Multitasking environments involve running multiple applications simultaneously.
• The CPU switches between these applications to create the illusion of parallel execution.