Operating System Objectives and Resource Allocation

Introduction to Operating Systems and Structures

• An operating system is an intermediary between a computer user and the computer hardware.
• Operating system goals include executing user programs, solving user problems, making the computer convenient, and using hardware efficiently.
• Key OS responsibilities include resource allocation, error prevention, and preventing improper computer use.

Computer System Architecture

• A computer system consists four components: hardware, operating system, application programs, and users.
• The hardware provides computing resources like CPU, memory, and I/O devices.
• The operating system controls and coordinates hardware use among applications and users.
• Application programs define how system resources solve user computing problems.

What Operating Systems Do

• Operating system importance varies depending on perspective. To most users convenience, ease of use, and good performance matters most.
• Shared computers must keep all users happy.
• Dedicated systems like workstations may share server resources.
• Handheld computers prioritize usability and battery life due to limited resources.
• Embedded computers in devices and automobiles often have minimal or no user interface.

Computer-System Architecture: Single vs. Multiprocessor Systems

• A single-processor system has one main CPU, executing a general-purpose instruction set.
• One CPU will handle instructions from user processes.
• Most systems use a single general-purpose processor, but many also have special-purpose processors.
• Multiprocessor systems, also known as parallel or tightly-coupled systems, are growing in popularity.
• Multiprocessors provide increased throughput, economy of scale, and increased reliability.
• With Asymmetric Multiprocessing, each processor is assigned a specific task.
• Symmetric Multiprocessing enables each processor to perform all tasks.
• Symmetric Multiprocessing shares memory for processors.
• Asymmetric Multiprocessing allows only the master processor to run tasks in OS.

Operating System Structure: Multiprogramming and Timesharing

• Multiprogramming (Batch system) needed for efficiency to avoid single user keeping CPU and I/O devices busy at all times
• Multiprogramming organizes jobs (code and data) so CPU always has one to execute.
• Job scheduling selects one job to run from a subset of total jobs in system, kept in memory.
• Operating system switches to another job once a job has to wait
• Timesharing (multitasking) that enables CPU to switch jobs so frequently in order to create interactive computing and ensure response time is less than 1 second.
• A process has at least one program executing in memory
• CPU scheduling occurs if several jobs are ready to run simultaneously
• Swapping moves processes in and out of memory if they lack memory space to run.
• Virtual memory makes it possible to execute processes not completely in memory.

Process Management

• The process is program in execution and a unit of work within such system
• A passive entity is program, and active entity is the process
• Memory, CPU, I/O, files, and initialization data needed for the process to accomplish its task
• Reclaim process termination requires reclaim of any reusable resources.
• Program counter specifying location of next instruction to execute has single-threaded process
• Multi-threaded process has a program counter per thread

Process Management Activities

• Process management involves creating, deleting, suspending, and resuming processes for user and system purposes.
• It also includes providing mechanisms for process synchronization, communication, and deadlock handling.

Memory Management

• The memory has all or some of the program all if its instructions must run for the purpose of execution.
• The memory has all or some of the data for the program to run.
• Optimizing CPU utilization, computer response to users, and determining content of memory at any given time are determined by memory management activities.
• Memory management involves tracking memory usage, deciding which processes and data move in/out, and allocating/deallocating memory space.

Storage Management

• The OS provides a logical, uniform view of information storage.
• The physical properties abstracted to logical storage units known as files, controlled by devices, for each medium.
• Files being often organised into directories for file-system management
• For determining who can access what through files, access control is a standard
• OS file management activities include creating/deleting files and directories, manipulating files/directories via primitives, mapping files onto secondary storage, and backing up files onto stable media.

Protection and Security

• Protection controls access of processes or users to resources defined by the OS.
• Defence against internal/external attacks is security.
• User identities (user IDs, security IDs), which consists of name, associated number, are determined by the systems to distinguish who can access what.
• User ID is associated with files and processes of that user to determine access control.
• User's set managed by Group identifier (group ID) which also associated with each process / files.
• User is able to change to effective ID with more rights should effective ID be used with more rights.

Distributed Systems

• Distributed computing involves interconnected. separate systems, potentially heterogeneous, and networked together.
• Commom communications path is TCP/IP for connecting to a Network.
• Features are supplied to systems through Network Operating System (NOS) through network.
• Communication scheme allows systems to exchange messages, giving a sense of using one illusionary system.
• Various networks used, including wired, wireless, and storage-area networks.

Computing Environments - Client-Server

• Computing now supplanted by smart personal computers, with many system now servers, and many responding to clients generated requests
• Clients request services (i.e., database) through Compute-server system
• Clients store and retrieve files with interface through File-server systems

Examples of Operating System

• Modern operating systems include Windows 8, 10, and 11, in adition to Windows Server 2016, Red Hat Linux, Ubuntu, Fedora and Mac OS
• Virtual Machine Monitors (VMM) like VMware Player or Virtualbox can execute VM that runs a different OS

Operating System Services

• Essential program, service, error detection, protection/security, I/O operations, and file system management services are handled bu the OS.
• The user interacts with services through interfaces and calls.

User Operating System Interface - CLI

• Direct command entry that allows, Command Line Interface (CLI), uses a command interpreter
• Direct command entry allows, which can be implemented in kernel or implemented by systems program
• Command interpreter fetches user made commands for execution after multiple flavors are implemented on shell
• Shell is used to adds new features when built in commands or program name
• If adding in new features requires adding a new type of file or process, adding new features doesn't require shell modification

User Operating System Interface - GUI

• User-friendly desktop interface is used for user input
• This metaphor interface usually includes mouse, keyboard, and monitor
• User input like Icons allow selection of files, programs, and various actions
• Various mouse buttons can be used for actions over objects in the interface such providing info, options or executing folders, the folder is a file/directory
• GUI is a result of the Xerox PARC innovation
• Commonly use mix of interfaces, many are CLI now includes Both such GUI, Microsoft Windows is GUI, and CLi (Command Shell), Apple OS is "Aqua Interface" GUI.

System Calls

• These calls are designed to give access to OS services, and serve as programming interfaces
• Written on high-level so that they could be accessed via program rather than the OS directly
• Most common are like API. Such Win32 for Windows, or POSIX API for POSIX based system (UNIX and Linux and Mac OS)
• Java API are also common for Java based systems.

Types of System Calls

• Main system calls consist of file, process, device management, in addition to information maintenance, communications, protection and more.
• Windows and Unix all implement the system calls that have to be executed regarding the aspects and features of the OS.

Operating-System Structure

• A layered approach breaks the OS to various number of levels so that operations could be controlled.
• Lower layers are the base towards relies, whereas the higher levels run on the services.
• Bottom layer is the hardware, and topmost layer is just the interface.
• Typical layers has structure of data and routiness that used on higher level for operations.

Virtual Machines

• Virtual machine treats all the system hardware including OS kernel as single unit.
• Such systems, like VirtualBox (which is free) will provide the OS with logical isolated processes with their own processors.
• Bare hardware are same, but interface are kept to the same and OS is kept completely intact with its processes.