What is an Operating System?

A program that acts as an intermediary between computer users and computer hardware
Operating System targets.

• Perform user programs and make user's problems easier to solve
• Facilitate computer systems to use
• Use computer hardware in an efficient way

Computer System Structure

The computer system can be divided into four components

Hardware  - Provides Basic Computing Resources CPU, Memory, I / O Device

Operating System - Controls and coordinates the use of hardware between different applications and users

Application Program - Defines the methods in which system resources are used to solve computing
Users problems

Word processor, compiler, web browser, database system, video game

User - People, machines, other computers

Four Components of a Computer system

Operating system Definition

• OS is a resource allocation
• Manages all the resources
• Decisions between conflicting requests for efficient and appropriate resource use
• OS is a control program
• Controls the execution of programs to prevent computer errors and inappropriate use
• No universally accepted definition
• When you order an operating system, everything ships a vendor But changes wildly
• "A program that runs on the computer at all times" is the kernel. Everything else is either System programs (ships with operating systems) or application programs

Computer Startup

• The Boot Strap program is loaded on power-up or reboot
• Usually stored in ROM or EPROM, commonly known as firmware
• Starts all aspects of the system
• Load operating system starts kernel and execution

Computer System Organization

• Computer-system operation
• One or more CPUs, device controllers connect via common bus providing access to shared memory
• Concurrent performance of CPUs and devices competing for memory cycle

Computer-System Operation

• I / O devices and CPUs can execute concurrently
• Each device controller is in charge of a particular device type
• Each device controller has a local buffer
• Captures CPU data from local memory from main memory / up to
• From the I / O device to the local buffer of the controller
• Device controller notifies the CPU that it has completed its operation because of an interrupt

Common Functions of interrupts

• Interrupt transfer control routine is usually controlled through interrupt vectors, which all service routine addresses include
• The obstructed architecture will save the address of the obstructed instructions
• The incoming blockage is disabled while another blockage is being processed to prevent an interrupted obstruction
• The trap is a software-generated interrupt that is caused by an error or user request
• An operating system is interrupted

Interrupt Handling

• Operating system protects the CPU's status by registering and storing the program counter
• Determines what kind of interference has occurred
• polling
• vectored interrupt system
• Different sections of the code determine what action should be taken for each type of interference

Interrupted Timeline

• System calls - requests the operating system to wait for user I / O to complete
• The device-status table contains an entry for each I / O device that reflects its type, address and status.
• The operating system indexes the I / O device table to determine the state of the device and modify the table entry. Include interruption

Direct Memory Access Structure

• Used for high-speed I / O devices that are capable of transmitting information closer to memory speed
• Device Controller transfers blocks of data from buffer storage directly into the main memory without CPU Interference
• Instead of one per bar, only one block per block is generated

Storage Structure

• Main memory - only large storage media that the CPU can access directly
• Secondary storage - Expansion of main memory which provides large non-volatile storage capacity
• Magnetic discs - Hard metal or glass platters, which are covered with the magnetic recording material
• The surface of the disc is divided logically into tracks, which are divided into sectors
• Disk controller determines logical interaction between device and computer

Storage Hierarchy

• Hierarchy storage system
• Speed
• Cost
• Instability

Caching  - copying information in the fast storage system; The main memory can be seen as the final cache

Caching

• Important principles at multiple levels (hardware, operating system, software) in a computer
• Temporarily used in slow storage information temporarily
• If there is information, then fast collection (cache) was checked to determine
• If so, then information directly from the cache (faster)
• If not, the data is copied into the cache and used there
• Cache is smaller than cache storage
• Cash Management Important Design Issues
• Cash size and replacement policy

Computer System Architecture

• Most systems use a single general purpose processor (PDA through mainframe)
• Most systems also have special purpose processors
• Multiprocessor systems are increasing in usage and importance
• Also known as parallel systems, tightly-coupled systems

Clustered System

• Like a multiprocessor system, but many systems are working together
• Commonly sharing storage via the storage-area network (SAN)
• Provides a high-availability service that avoids failures
• There is a machine in the hot-standby mode in asymmetric clustering
• Symmetric clustering has several nodes, which monitor each other
• Some clusters are for high-performance computing (HPC)
• Apps must be written to use parallelization

Operating System Architecture

• Multiprogramming is needed for efficiency
• A single user can not keep CPU and I / O devices busy at all times
• Organizes multiprogramming jobs (code and data), so the CPU always has the same
• A subset of total jobs in the system is kept in memory
• One job is selected and run through job scheduling
• When it has to wait (for example I / O), OS goes to another job
• Timesharing (multitasking) is a logical extension in which CPU users are employed so often
• Interacting with each task, creating interactive computing
• Response time must be <1 second
• Each user has at least one program performed in memory [process
• f many jobs are ready to run at the same time [CPU scheduling
• If the processes do not fit in memory, swapping takes them in and out to run them.

Virtual memory allows complete execution of processes not in memory Memory layout for the multiprogrammed system

Operating System Operation

• Handheld Powered by Hardware
• Software error or request creates exceptions or traps
• Zero division, request for operating system service
• Other process problems include infinite loops, processes that modify one or the other operating system
• The dual-mode operation allows OS to protect itself and other system components
• User mode and kernel mode
• Provided by mode bit hardware

User Transitions in Kernel Mode

• Timer to prevent endless loop/process hogging resources
• Set interrupt after a specific period
• Operating system reduction counter
• When the counter zero creates an obstacle
• Set prior to the scheduled procedure before getting the prescribed control or eliminating the program that exceeds the allotted time.

Operating System Function

Process Management

• There is a program in process execution. It is a unit of work within the system. A program is a passive unit,
• A process is an active unit.
• The process requires resources to complete its work
• CPU, memory, I / O, files
• Initial data
• The need to recover any reusable resources for the end of the process
• In the single-threaded process, there is a program counter that is to specify the location of the next instruction to execute
• Process sequentially executes instructions until it is completed at one time
• In multi-threaded process per thread is a program counter
• Usually, there are several processes in the system, some users, some operating systems are running concurrently on one or the other
• More CPU
• Consciousness by multiplying the CPU into processes/threads

Process Management Activities

• The operating system is responsible for the following activities in relation to the process Management 
• Creating and deleting both user and system processes
• Suspend and resume processes
• Providing mechanisms for process synchronization
• Providing mechanisms for process communication
• Providing mechanisms to combat deadlock

Memory Management

• All data in memory before and after processing
• To perform all the instructions in memory
• Memory management determines what is in memory when
• Optimize CPU usage and computer response for users
• Memory management activities
• Keep in mind, which parts of memory are currently being used and by whom it is being done
• Decide which process (or its parts) and data to move to memory
• Allocating and Dealing Memory Space as needed

Storage Management

• OS provides a similar, logical approach to information storage
• Logical storage unit physical properties - file
• Each medium is controlled by the device (i.e., disk drive, tape drive)
• Different properties include speed, capacity, data transfer rate, access method (sequential or). Random)
• File system management
• Files are usually organized in directories
• Access control on most systems to determine who can access
• OS activities are included
• Creating and deleting files and directories
• Primitives to manipulate files and diaries
• Mapping files on secondary storage
• Backup files on static (non-volatile) storage media

Mass Storage Management

• Usually, the disk is used to store data that does not fit in main memory or data that should be kept for "long" The period of time
• Proper management is of central importance
• The full speed of computer operation lies on the disk subsystem and its algorithm
• MASS STORAGE ACTIVITIES
• Free space management
• Storage allocation
• Disk scheduling
• Some storage is not fast enough
• Tertiary storage includes optical storage, magnetic tape
• Still needs to be managed
• The change between WORM (writing-once, read multiple times) and RW (read-write)

Performance of Various Stages of Storage

Migration in the Register from the Disk of Integer A

• The multitasking environment should be careful to use the most recent value, no matter where it is stored in Storage hierarchy

• Multiprocessor environment should provide cache compatibility in hardware such as all CPUs The most recent value in their cache
• The situation of a distributed environment is even more complex
• Many copies of datum may be present

I / O Subsystem

• One purpose of the OS is to hide the specificity of hardware devices from the user
• The I / O subsystem is responsible for
• Memory management of I / O including buffering (data is being temporarily stored while it is being transferred), Caching (storing parts of data in fast storage for display), spooling (overlapping of output) A job with the input of other jobs)
• Common Device-Driver Interface
• Drivers for specific hardware devices

See: What is Database?

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