Operating System: Definition and Goals

Operating System Basics

• The operating system (OS) acts as an intermediary between a user and the computer hardware.
• An OS is a collection of programs that manage a computer's operations.
• Examples of operating systems include UNIX, Mach, MS-DOS, MS-Windows, Windows/NT, OS/2, MacOS,VMS, and MVS

Operating System Goals

• Execute user programs to solve user problems easily.
• Make the computer system convenient and efficient to use.
• Use computer hardware efficiently.

Computer System Components

• Hardware provides the basic computing resources, such as the CPU, memory, and I/O devices.
• The operating system controls and coordinates the use of hardware among application programs and users.
• Application programs use system resources to solve users' computing problems, including compilers, database systems, video games, and business programs.
• Users can be people, machines, or other computers.

Operating System Definitions

• The OS manages and allocates resources.
• It controls the execution of user programs and I/O device operations.
• The kernel is the primary program running at all times, with other programs considered applications.

Components of OS

• The OS comprises the Kernel and Shell.
• The kernel is a constant, active part of the OS that interacts directly with the hardware, (e.g., device drivers, DLL files, system files).
• The shell functions as a command interpreter, enabling user interaction with application programs and executing OS instructions, namely commands.

User Perspective

• The OS is designed for user convenience, maximizing user work and ease of use.

System Perspective

• From a computer standpoint, an OS is a control program managing user program execution to prevent errors and ensure proper computer use
• It focuses on the operation and control of I/O devices

Operating System Functions

• Manages and allocates resources to processes, including CPU time, memory, files, and I/O devices
• Activities include process creation, deletion, suspension, and resumption and also provides mechanisms for process synchronization and communication

Main-Memory Management

• Memory is a quickly accessible data repository shared by the CPU and I/O devices
• The OS tracks memory usage, decides which process to load when space is available, and allocates/deallocates memory.
• Main memory is a volatile storage device and loses contents upon system failure

File Management

• A file is a collection of related data, representing programs or data.
• Activities include file/directory creation and deletion and also provides primitives for file/directory manipulation
• It also maps files onto secondary storage and performs file backups

I/O System Management

• The I/O system includes a buffer-caching system, a general device-driver interface, and drivers for specific hardware.

Secondary-Storage Management

• Due to main memory limitations, secondary storage is needed and disks are the primary online storage
• The OS manages free space, allocates storage, and schedules disk usage

Networking

• A distributed system is a networked collection of processors with their own local memory
• Processors communicate via a protocol over a communication network
• Distributed systems enable user access to system resource and allow computation speed-up

Data Management

• A protection system controls access to system and user resources, distinguishing between authorized and unauthorized use.
• It specifies controls and provides enforcement.

Command-Interpreter System

• The system interprets control statements to manage processes, I/O, storage, memory, file access, protection, and networking.
• The read-and-interpret program is called a command-line interpreter or shell; it gets and executes command statements.

Operating-System Structures

• OS structure includes system components, services, calls, programs, structure, virtual machines, design/implementation, and generation.

Common System Components

• The components are process management, main memory management, file management, I/O system management, secondary management, networking, protection system, and command-interpreter system.

Evolution of Operating Systems

• Mainframe systems reduce setup time with job batching and automatic job sequencing using a resident monitor.

Batch Processing

• OS groups jobs with similar requirements for efficient processing, managed by a computer operator
• It schedules jobs by priority and resource needs.

Multiprogramming

• This OS executes multiple jobs simultaneously on a single processor, increasing CPU utilization
• Jobs are stored in a job pool in the disc, loaded into main memory, and switched during I/O waits
• It uses job scheduling and CPU scheduling

Time-Sharing/Multitasking

• A logical extension of multiprogramming that enables faster job switching and simultaneous user access
• Users interact with running jobs with the use of virtual memory
• Includes CPU scheduling, memory management, disc management, and security management
• Examples: CTSS, MULTICS, CAL, and UNIX

Multiprocessor Systems

• In these parallel or tightly coupled OS, processors share the computer bus, clock, and sometimes memory and peripherals
• Provide increased throughput, economy of scale, and reliability where throughput increases as processors are simply added
• If one processor fails, others take over, offering graceful degradation or fault tolerance

Multiprocessor classifications

• Symmetric multiprocessing: each processor runs an identical copy of the OS, communicating as needed.
• Asymmetric multiprocessing: features a master processor controlling slave processors, scheduling jobs, and managing memory.

Distributed Operating Systems

• In a distributed system, machines are networked, each with its own processor and local memory.
• The OS across machines collaborates to manage network resources
• Can be classified into Client-Server or Peer-to-Peer systems.

Advantages of distributed systems

• Resource sharing
• Computation speed up via load sharing
• Reliability
• Communications
• Requires networking infrastructure, such as LAN or WAN

Personal Computer Systems

• The OS is designed for maximizing user convenience and responsiveness, without multi-user or multi-tasking capabilities.
• Including systems like Microsoft Windows, and Apple Macintosh.

Real-Time Operating Systems (RTOS)

• These OS are meant for applications with fixed deadlines and used in embedded systems, automobile engine controllers, industrial robots, spacecraft, and industrial control systems.
• Classified into hard real-time systems (guarantee task completion on time) and soft real-time systems (prioritize real-time tasks).

Operating System Services

• Providing user convenience
• Program execution: enabling the user to run programs by allocating/deallocating memory and scheduling the CPU
• I/O Operations: making it more convenient for user to run programs
• File system manipulation
• Communications
• Error Detection

System Services for Efficient Operation

• Resource allocation: managing and allocating resources when multiple users/jobs are running
• Accounting
• Protection

System Calls

• System calls provide an interface that allow user-level processes to request services from the operating system
• System Calls perform services such as process control, file management, device management, information maintenance, and communications.

Operating System Structures

• An Operating system layer introduces new operations and existing operations

Microkernel System Structure:

• Transports as much from the kernel into the "user" space.
• Communication between user modules takes place using message passing

Advantages of Microkernel System Structure

• Easier to extend a microkernel system structure
• Easier to port the operating system to new architectures
• More reliable with more reliability because less code is running in kernel mode
• More secure

Virtual Machines

• A virtual machine uses a layered approach.
• A virtual machine treats hardware and the operating system kernel as the underlying hardware.
• Provide an interface identical to bare hardware, and Creates the illusion of multiple processes on their own processors with memory

Advantages of Virtual Machines

• Complete protection of system resources because each virtual machine is isolated from all others
• Ideal for OS research and development, since system development is done on the virtual machine without disrupting normal system operation.
• Requires effort to provide an underlying machine exact duplicate

System Generation (SYSGEN)

• The system must be configured for each specific computer site which is know as system generation (SYSGEN).
• SYSGEN program obtains information concerning the specific configuration of the hardware system.
• Kinds of information: such as what CPU will be used?, What devices are available? What operating-system options are desired?

Booting

• Starting a computer by loading the kernel
• Includes a bootstrap program in ROM to locate and load the kernel into memory.

Computer-System Architecture

• Includes CPU, disk controller and printer.

Computer-System Operation

• A description of concurrent operations of the I/O device and the CPU.

Functions of Interrupts

• An interrupt transfers control to the interrupt service routine through the interrupt vector.
• Interrupts save the address of interrupted instruction and disable the incoming interrupts.

Interrupt Handling

• Involves the operating system preserving the state of the CPU by storing registers and the program counter
• Determines the type of interrupt and also uses separate segments of code determine action for type of interrupt

I/O structure

• Describe what happens to the I/O after its starts. Including information on system calls.
• In simple systems, after I/O starts, control returns to user only upon completion.
• Include a device-status table with an entry for each I/O device.

Two I/O Methods

• Synchronous (after I/O starts, control returns to user program only upon I/O completion.)
• Asynchronous (after I/O starts, control returns to user program without waiting for I/O completion.)

Direct Memory Access (DMA)

• Structures that allow high-speed I/O at memory speeds
• A Device controller which has a local buffer transfer blocks of data directly to main memory without CPU intervention

Storage Structure

• Main memory is the only storage that the CPU can access directly
• Secondary storage is an extension of main memory by providing large of nonvolatile storage capacity

Magnetic disk

• Involves rigid metal and class platters covered in recording metallic material
• Logically divided into sectors and tracks through the use of disk conttoller

Storage Hierarchy

• Is organized in a hierarchy by speed, cost and volatility.
• Caching - copying information into faster storage system; main memory can be viewed as a last cache for secondary storage

Hardware Protection

• Uses dual mode and must protect I/O, memory and the CPU

Dual Mode Operation

• Enables the Operating System to ensure that an incorrect program cannot cause other programs to execute incorrectly by use of operations known as user mode and monitor mode.
• User mode is execution done on behalf of a use
• Monitor mode (also kernel mode or system mode) – execution done on behalf of operating system

I/O Protection

• Requires all I/O instructions to be privileged instructions so that a user program could never gain control of the computer in monitor mode

Memory Protection

• Requires memory protection at least for interrupt vector and interruption service routines
• Add two registers that determine the range of legal addresses a program can access (base register and limit register)

CPU Protection

• Implementation of a timer that interrupts computer after specified period to ensure operating system maintains control

Process Concept

• A process is an active program, including code, program counter, registers, stack, and data section.
• Operating systems execute jobs or tasks.
• A process includes a program counter stack and data section, which executes in sequential manner

Process State

• The phases of a process are new, running, blocked/waiting, ready, and terminated.
• Program is a static object whereas a process is a dynamic object residing main memory

Process Control Block (PCB)

• Each process is associated with information, including process state, program counter, CPU registers, CPU scheduling, memory management, accounting, and I/O status.,

Process Scheduling Queues

• The Job Queue consists of all processes in the system
• The ready queue consists of the processes that are residing in main memory and are waiting to execute by CPU
• Device Queue consists of all the processes that are waiting for a particular I/O device

Schedulers

• Schedulers decide which processes to move between queues, and allocates the CPU
• Long-term scheduler or job scheduler loads processes from disk into memory, executing infrequently
• Short-term scheduler or CPU scheduler selects a process from those ready and allocates CPU
• The Medium-term scheduler schedules the processes as intermediate level of scheduling

Context Switch

• When the CPU switches to another process, the system preserves state of old process and load the state of the new process

Inter-Process Communication (IPC)

• A process mechanism provides services for other processes to communicate on another and to synchronize their actions.
• Messages are transferred with fixed or variable size

Synchronization Hardware

• Hardware features can make programming task easier and improve efficiency, and this includes simple instruction which are available on the systems

Process creation

• Parent processes create children, forming a process tree
• Parent and children share or do not share resources
• Execution: parent and children execute concurrently or parent waits
• Address space: child duplicates or has a new program

Process termination

• Occurs by executing the last statement (exiting)
• The parent may terminate the execution of children (abort)

Cooperating Processes

• May be either independent processes or processes that are cooperating. Each are able to affect both system and data integrity

Mutex

• A method of locking a data structure, such as an object, to only allow access from one thread.
• Protect the variables and is also used when large number of threads come on particular processes

CPU Scheduling

• Includes Basic Concepts of scheduling, including basic concepts, scheduling Criteria, scheduling Algorithms, Multiple-Processor Scheduling and Algorithm Evaluation

Process Scheduling Queues

• Processes is used to among the one selected among main memory that are ready to execute, and allocates the CPU to one of then
• Switches from running to waiting state, running to ready state, waiting to ready and terminating

Dispatcher

• Gives control of the CPU to the process selected by the short-term scheduler involving. switching to user mode & jumping to a proper location in the user program.

Scheduling Criteria

• Cpu Utilization
• A throughput (number of the process that completed execution per time unit

Optimization Structure

• Min response time
• Max CPU Utilization

First come first Served Scheduling

• By for the simplest cpu algorithm is the first come first served. First process requests the cpu first this system is allocated the time
• Shortest job First Scheduling
• Is a different approach to Cpu scheduling is the smallest job first scheduling is to associate with reach process the end of the ladders new cpu Burst.

Priority Scheduling

• The SJF scheduling as an algorithm in a special case of the general priority scheduling algorithm. With each process the allocation of a higher priority

Round Robin scheduling

• The round-robin scheduling algorithm is design especial for the times in history time sharing system.
• It is similar to Fcfs scheduling for preemption id added to switch between process.

Preemptive Scheduling:

• A solution in place the scheduling of the algorithms can be divided into algorithm in the category and to what they can make sure

Non Preemptive scheduling:.

• A scheduling division into a discipline from non process and once process come back to use the cpu comes

Threads

• Threads sometimes called a lightweight process is a basic unit of CPU
• utilization is comprising a thread Id, a program counter, a register set up a stack as it shares with other threads in the same process if code the data section and also system resources

Benefit

• A major categories of programming are broken down into four sections responsiveness for multi threading interactive programming and that can allow a Program to continue or make it increase throughput

User level threads

• User level threads implement in user level libraries rather than system costs of read switching does not need an operating system caused interrupt to the kernel

Kernel threads

• Kernel level thread in that the kernels known as managing all the threads of certain threads which is the canal has a thread table it keeps track all threads

Disadvantages of user level threads

• Disadvantages of user level threads also is that if they all are used without thread table they will have no support and must be provided

Advantages of kernel threads

• Kernels will always have knowledge of who is on this threads which a shadow lay decide which a thread needs to give more time to run

The One to One Model

• Maps each user thread on a kernel thread.
• The only drawback to this model is that creating user thread requires creating a corresponding kernel thread.

The Many-to-Many Model

• Multiplex is many user level threads to smaller or equal number of kernel threads

Process Communication

• A set of process is in deadlock state if it's process waiting for each other
• A deadlock state process has the resource being requested to use those are all
• The term Deadblock the system because the other needs resources by the other and no process is to hold those resources

Preemptable and Nonpreemptable Resources

• In an operating system the resources in preemptable and non preemptable resources comes with resource and resource

Necessary conditions for Deadlock

• (Coffman 1971): identified 4 conditions that must hold simultaneously for there to be a deadlock like mutual exclusion connection and hold up and wait condition

Interprocess communication

• Process must name each other explicitly to send a direct communication or establish a communication is associated

Synchronzation hardware.

• The operating system used synchronization to access their to to what to do after that

Semaphores

• The best possible solution that is known in this document is known to be semaphores and have variable operation called wait

Communication Between Processes

• Takes place by calls to send and receive primitives.
• There are different design options for implementing each primitive.
• Message passing may be either blocking or nonblocking-also known as synchronous and asynchronous.

Blocking send:

• The sending process is blocked until the message is received by the receiving process or by the mailbox.

Nonblocking send:

• The sending process sends the message and resumes operation.

Blocking receive:

• The receiver blocks until a message is available.

Nonblocking receive:

The receiver retrieves either a valid message or a null.

Buffering

• Whether the communication is direct or indirect, messages exchanged by communicating processes reside in a temporary queue.
• Basically, such a queue can be implemented in three ways: Zero capacity, is Bounded capacity, or Bounded capacity

Direct Communication

• Used so that processes are naming each other explicitly - process send messages to process Q and it has links for two each communicating processes

Deadlock Prevention

• Is known to be the process the the that the system must have the system as It takes more steps to create

Detection of aDeadlock

The steps in general on this is a deadlock if it's found in the way

1.Single Instance

We make sure there is only one instance of each type of resource. and follow this with. Removing the nodes of type

Process Termination

A method of aborting all death locked that is the process

Resource preemption

The memory that is being freed from each task as a resource and we need to work on three needs

####Memory Management the system has to divided between two types on how to process the the memory from

Binding and data instructions to

• Address binding of instructions and data to memory addresses can happen at three different stages known as: compile time, load time or execution time

Dynamic Linking

• With this linking, Linking postponed until execution time. where Small piece of code (stub) used to locate the appropriate memory-resident library routine

Overlays

• the memory is needed a bit it's needed to a great way at any point in time

Swapping

The memory takes a different way and the the way to start the process of with out

Memory Allocation

• The main memory must accommodate both the operating system and the various user processes. We need to allocate different parts of the main memory in the most efficient way possible. The main memory is usually divided into two partitions: one for the resident operating system, and one for the user processes. We may place the operating system in either lowmemory or high memory. The major factor affecting this decision is the location of their interrupt vector.

Two of the following is how to use memory for user processes:

• 1. Contiguous memory allocation
• 2. Non contiguous memory allocation
• 1. Contiguous Memory Allocation all of our processes are stored in contiguous memory locations.

What is Memory compaction?

• Compact to reduce external fragmentation.

Hardware Support:

• The relocation register scheme also used to protect user processes.

Noncontiguous memory allocation

It is allowed to store the processes in Noncontiguous memory

There are different techniques used to load processes into memory, as follows:

1. Paging
2. Segementation
3. Virtual memory paging(Demand paging) etc.

Two Major allocation Algorithm:

• Equal allocation
• Proportional allocation

Page Table

• The processes that can come from and to and from the harddrive are found here and then all have to be worked on