Operating System Concepts-1

Operating System Concepts

Operating System ConceptsUnit-1: Computer System OrganizationM. Abu Baker SiddiqueOperating System is the most important program that runs on a computer and therefore the study of operating systems is fundamental to the students of computer sciences1.1 Basic Components of Computer SystemA computer system is considered a combination of basic hardware components.These components are organized into a well designed style to form the computer systemComponents of Computer System

1.1.1 Central Processing Unit(CPU)CPU acts as a brain of the computerIt is an electronic device about a inch squareIt contains CU and ALUIt has also some special purpose registers

Dual Core/Multi Core CPUs

1.1.2 Main MemoryMain Memory refers to physical memoryAlso called RAMData must be stored before/after processingIt also contains main part of OS every timeAn other name of it is Primary memory It is volatile memorya transistor and a capacitor is needed to build a single cell i.e to store a single bit of dataMain Memory

1.1.3 Input / Output ModulesThe computer will be of no use if it is not communicating with external world.I/O devices send and receive data from/to computerAlso called peripheral deviceEach I/O device has its own controller

Input / Output Devices

1.1.4 System BusA system bus is a single communication path.It connects the major components of a computer system

System BusesData Bus: is the most common type of bus. It is used to transfer data between different component of computerAddress Buss: Many components are connected to one another through buses. Each component is assigned a unique ID. This ID is called address.Control Buss: is used to transmit different commands or control signals from one component to another component.

1.1.5 CPU RegistersCPU register is a small amount of storage available as part of a CPU. Registers can be accessed more quickly.

CPU Registers continued..Memory Address Register (MAR): this register holds the address of memory where CPU needs to reads or write data.Memory Buffer Register (MBR): This register holds the contents of data or instruction read from, or written in memory.I/O Address Register(I/O AR): is used to specify the address of a particular I/O device.CPU Registers continued..I/O Buffer Register (I/O BR): is used for exchanging data between the I/O module and the processor.Program Counter Register (PCR): is also known as Instruction Pointer Register (IPR). This register is used to store the address of the net instruction to be fetched for execution.Instruction Register (IR): Once an instruction is fetched from main memory, it is stored in the IR.CPU Registers continued..Accumulator Register (AR): is located inside the ALU. It is used during arithmetic & logical operations of ALU.Stack Control Register (SCR): a stack represents a set of memory blocks. The data is stored in and retrieved from these blocks in an order.Flag Register (FR): is used to indicate occurrence of a certain condition during and operation the CPU.1.2 Instruction Execution CycleEvery single statement of a computer program is called machine instruction. FetchDecodeExecuteStore

1.3 Computer System ArchitectureComputer System Architecture means construction/design of a computer. There three principal ways to connect components of a computer.Von Neumann ArchitectureBus ArchitectureSingle & Multiprocessor architecturesComputer System ArchitectureVon Neumann Architecture: John Von Neumann explained the first practical stored program computer architecture in 1940s.Components of it, Input, Output, Processor, Memory, Data-Path.The speed is dependent on the bandwidth of the data path b/w processor and memory.It is called Von Neumann bottleneck.Von Neumann Architecture

1.3.2 Bus ArchitectureBus is like a supper highwayProcessor and memory are connected through it.Data moves on the bus between CPU and Memory.It has same components as the Von Neuman Difference is bussBus Architecture

1.3.3 Single & Multiprocessor ArchitectureA computer system may be organized in different ways. Computer may have single processor or multiprocessorThere two types of itSingle Processor SystemMultiprocessor System1.3.3.1 Single Processor SystemSmall computers use only one processorI/O devices may have their own small processor that helps to move data quickly

1.3.3.2 Multiprocessor SystemIn multiprocessor system tow or more general purpose work togetherMore than one program can be executed on different processor at same time.Also known as multi processingOSs are also made according to multiprocessor.Also known as parallel systemsIt is very fast.1.3.3.2 Multiprocessor SystemThere are two types of Multi processor systems.Asymmetric multiprocessing systemsSymmetric multiprocessing systemsAsymmetric Multiprocessor SystemEach processor is assigned a specific taskOne processor work as master and other as slave processors.Master processor controls the operations of the system.

Symmetric Multiprocessor SystemMultiprocessor works together on the same taskEach processor can perform all type of tasksEvery one is equal

1.4 Clustered SystemsClustered system is another form of multiprocessor systemThese are full fledge systemsSystems contains multiprocessorsBut design is different multiprocessorsIndividual systems are connected/clustered together vial LAN.One of them is monitoring machineOne take ownership if other is failed

Clustered Systems

Clustered Systems continuedThese are very helpful in DR environment.A layer of cluster software runs on the cluster node.Use one storage device SANThere are two types of it:Asymmetric Clustered SystemSymmetric clustered System

1.4.1 Asymmetric Clustered SystemOne machine is in hot standby modeOther machine is running the applicationHot-standby does nothingOnly monitor the active serverIf server fails, it takes the control1.4.2 Symmetric Clustered SystemEvery machine run the applicationAlso monitor each otherIt is efficient modAll the resources are used equallyOnly used in more than one application.ThankS