OPERATING SYSTEM(2140702) 1 Prepared by: Dr. Vipul Vekariya Ph. D(CSE) NGI-JUNAGADH
TEACHING SCHEME Lecture Lab Credit 4 2 6 2
SYLLABUS 3
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REFERENCE BOOKS/TEXT BOOK 6
CONTENT OF THE CHAPTER. ØWhat is an operating system ØHistory of operating systems ØThe operating system zoo ØComputer hardware review ØOperating system concepts ØSystem calls Ø Operating system structure 7
OPERATING SYSTEM A modern computer system consist of one or more processor, main memory, disk, keyboard, network interface and other I/P and O/P Devices. Writing programs that keep track of all these component and use them correctly and optimally. For this reason computers are equipped with a layer of software called operating system. Whose job is to manage all the devices and provide user programs with simpler interface to the hardware. A program that controls the execution of application programs and act as an interface between applications and hardware 8
MAIN OBJECTIVES OF AN OS: Convenience: An OS makes a computer more convenient to use. Efficiency: An OS allows the computer system resources to be used in an efficient manner. Ability to evolve: An Os should be constructed in such a way as to permit the effective development , testing and introduction of new system function. 9
Fig -1. A computer system consists of hardware, system programs , application programs 10
INTRODUCTION The lowest level contains physical devices, consisting of integrated chips, wires, power supplies, cathode ray tube, and similar physical device. Next comes micro architecture level, in which physical devices are group together to form functional units. This level contains some register internal to the CPU and data path containing an ALU. The operation of data path is controlled by software, called the micro program. The purpose of this data path is to execute some set of instruction. ISA ( Instruction set Architecture) ( Machine Language) This instruction may use the register or other hardware facilities. 11
The machine language has between 50 to 300 instruction. Device register: To control the I/p & O/P Devices. Operating system: To hide all this complexity. It consist of layer of software. Example : Read the block from Hard disk. On the top of the OS is the rest of the system software and application software. This is not a part of the operating system. The OS is that the portion of the software that run in KERNEL mode or supervisor mode. It is protected by the user tampering by the hardware. Compilers and editors are run in user mode. It is very difficult to draw a boundary between kernel mode and user mode. ( Example: Password protection, file system) 12
WHAT IS AN OPERATING SYSTEM It is an extended machine( as a User/Computer interface) • • • § § Hides the messy details which must be performed Presents user with a virtual machine, easier to use The program that hides the truth about hardware from programmer and present a nice and simple view. Most basic command is read and write. Each of which require 13 parameter passed by OS to read and write. For example address of disk block, the number of sector per track, the recording mode, the intersector gap spacing etc…. In this view function of operating system is to present the user with the equivalent of an extended machine or virtual machine. That is easier to program than underlying hardware. 13
OS AS RESOURCE MANAGER
It is a resource manager Each program gets time with the resource Orderly and controlled allocation of the various job to processor, memories, i/p and o/p devices. The task of operating system is to keep track of v who is using which resource v to grant resource request v to account for usage v handling and manage conflicting request Resource management includes sharing resource in two ways: q Time sharing examples: Printer, CPU, q Space sharing Example: Memory, Hard disk. 15
HARDWARE SOFTWARE CORRESPONDENCES 16
SERVICES PROVIDED BY THE OPERATING SYSTEM Program development Editors and debuggers. Program execution OS handles scheduling of numerous tasks required to execute a program Access I/O devices Each device will have unique interface OS presents standard interface to users Controlled access to files Accessing different media but presenting a common interface to users Provides protection in multi-access systems System access Controls access to the system and its resources 17
SERVICES CONT… Error detection and response Internal and external hardware errors Software errors Operating system cannot grant request of application Accounting Collect usage statistics Monitor performance 18
EVOLUTION OF OPERATING SYSTEMS Operating systems will evolve over time Hardware upgrades plus new types of hardware New services Fixes
EVOLUTION OF OPERATING SYSTEMS It may be easier to understand the key requirements of an OS by considering the evolution of Operating Systems Stages include Serial Processing Simple Batch Systems Multiprogrammed batch systems Time Sharing Systems
SERIAL PROCESSING With the earliest computers (late 1940 s to the mid-1950 s), the programmer interacted directly with the computer hardware; There was no OS. • These computers were run from a console consisting of display lights, toggle switches, some form of input device, and a printer. • Programs in machine code were loaded via the input device (e. g. , a card reader). •
PROBLEM WITH SERIAL PROCESSING • • • Scheduling Most installations used a hardcopy sign-up sheet to reserve computer time. Typically, a user could sign up for a block of time in multiples of a half hour or so Setup time A single program, called a job, could involve loading the compiler plus the high-level language program (source program) into memory, saving the compiled program (object program) and then loading and linking together the object program and common functions. Each of these steps could involve mounting or dismounting tapes or setting up card decks. If an error occurred, the hapless user typically had to go back to the beginning of the setup sequence. 22
SIMPLE BATCH SYSTEM Early computers were extremely expensive Important to maximize processor utilization The central idea behind the simple batch-processing scheme is the use of a piece of software known as the monitor. Monitor Software that controls the sequence of events the user submits the job on cards or tape to a computer operator Batch jobs together sequentially and places the entire batch on an input device Program returns control to monitor when finished
MONITOR’S PERSPECTIVE Monitor controls the sequence of events Resident Monitor is software always in memory Monitor reads in job and gives control Job returns control to monitor
MODES OF OPERATION User Mode User program executes in user mode Certain areas of memory protected from user access Certain instructions may not be executed Kernel Mode Monitor executes in kernel mode Privileged instructions may be executed, all memory accessible.
MULTIPROGRAMMED BATCH SYSTEMS CPU is often idle Even with automatic job sequencing. I/O devices are slow compared to processor
UNIPROGRAMMING Processor must wait for I/O instruction to complete before preceding
MULTIPROGRAMMING When one job needs to wait for I/O, the processor can switch to the other job
MULTIPROGRAMMING
EXAMPLE
UTILIZATION HISTOGRAMS
MULTIPROGRAMMING BATCH SYSTEM Most important features that is useful for multiprogramming is the hardware supports. Interrupt driven I/O and DMA(direct memory access) 32
TIME SHARING SYSTEMS Using multiprogramming to handle multiple interactive jobs Processor’s time is shared among multiple users Multiple users simultaneously access the system through terminals
BATCH MULTIPROGRAMMING VS. TIME SHARING
PROBLEMS AND ISSUES Multiple jobs in memory must be protected from each other’s data File system must be protected so that only authorised users can access Confliction for resources must be handled Printers, storage etc
HISTORY OF OPERATING SYSTEMS First generation 1945 - 1955 Second generation 1955 - 1965 transistors, batch systems Third generation 1965 – 1980 vacuum tubes, plug boards ICs and multiprogramming Fourth generation 1980 – present personal computers 36
THE OPERATING SYSTEM ZOO Mainframe operating systems Server operating systems Multiprocessor operating systems Personal computer operating systems Real-time operating systems Embedded operating systems Smart card operating systems 37
MAIN FRAME OPERATING SYSTEM § § This operating system used for main frame computers. . Those room sized computers still found in major corporate data centers. This OS for mainframe are heavily oriented towards processing many jobs at once. This OS used where need of more I/O Operation. They typically offer three kind of service. 1) Batch 2) Transaction processing 3) Time sharing it is used for large scale electronic commerce site and server for B 2 B transactions. OS/360, IBM CP/67, IBM/System 360 38
SERVER OPERATING SYSTEM One level down are the server operating system It run on server which are either very large personal computer. They serve multiple users over a network at a once. User share hardware and software resources. Example: print service, file service, web service. UNIX and windows 2000 are server OS. 39
MULTI PROCESSOR OS Multi processor in a single system. That required Multi processor OS. These are variation on server operating system. This system are called parallel computers. Windows and LINUX run on multiprocessors. Personal Computer OS: Its job is to provide a good interface to a single user. They are widely used for word processing, spread sheets, and internet access. Example: WIN 98, XP, VISTA, Macintosh 40
REAL TIME OS It is a multitasking operating system that aims at executing real-time applications. Time is key parameter. The main object of real-time operating systems is their quick and predictable response to event Industrial process control system EMBEDDED OS The operating systems designed for being used in embedded computer systems are known as embedded operating systems. . They are designed to operate on small machines like PDAs with less autonomy. They are very compact and extremely efficient by design. Windows CE, Free. BSD and Minix 3 are some examples of embedded operating systems. 41
SMART CARD OS The smallest OS run on smart card. Which are credit card sized devices containing a CPU chip. ROM is on the smart card chip and JVM ( java virtual machine) is installed. 42
A COMPUTER’S BASIC ELEMENTS Processor: control the operation of computer and perform its data processing function. Main Memory: Stores data and program I/O Modules: move data between the computer and its external environment. (secondary storage, Communication equipments) System Bus: Provides for communication among processor, main memory and I/O modules. 43
PROCESSOR It is brain of the computer system. It fetch the instruction from memory and execute it. Each CPU contains the some register inside to hold a key variables and temporary results. Four internal registers Memory address resister (MAR): it contains the address of memory for data read or write. Memory buffer register (MBR): it contains the data to be written or read from memory. I/O address register: Specify particular I/O device I/O buffer register: exchange data between and I/O module and processor 44
TOP-LEVEL VIEW
PROCESSOR(CONTI. ) 1) 1) Processor contains two types of register. User visible register : user can access or see the data of this register using assembly language Control and status register: used by the processor to control the operation of the processor. 46
USER VISIBLE REGISTER Data register: contains the data of program Address register: contains the main memory address of data or instruction. Index register: to find the effective address of program. Stack pointer: point to the top of the stack contains in memory 47
CONTROL AND STATUS REGISTER Program counter(PC): contains the address of the next instruction to be fetched. Instruction register(IR): contains the instruction most recently fetched. PSW( Program status word): it contain the condition code bits, which are set by comparison instruction, the CPU priority, the mode( user or kernel) and various other control bits. 48
INSTRUCTION EXECUTION A program consists of a set of instructions stored in memory Two steps Processor reads (fetches) instructions from memory Processor executes each instruction 49
BASIC INSTRUCTION CYCLE
INSTRUCTION FETCH AND EXECUTE The processor fetches the instruction from memory Program counter (PC) holds address of the instruction to be fetched next PC is incremented after each fetch Fetched instruction loaded into instruction register Categories Processor-memory: Data may be transferred from processor to memory or from memory to processor. Processor-I/O: Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module. Data processing: The processor may perform some arithmetic or logic operation on data. Control: An instruction may specify that the sequence of execution be altered. 51
EXAMPLE OF PROGRAM EXECUTION
INTERRUPTS Interrupt the normal sequencing of the processor Provided to improve processor utilization Most I/O devices are slower than the processor Processor must pause to wait for device The length of this pause may be on the order of many thousands or even millions of instruction cycles. • Clearly, this is a very wasteful use of the processor. 53
FLOW OF CONTROL WITHOUT INTERRUPTS
INTERRUPTS AND THE INSTRUCTION CYCLE
TRANSFER OF CONTROL VIA INTERRUPTS
INSTRUCTION CYCLE WITH INTERRUPTS
SIMPLE INTERRUPT PROCESSING
INTERRUPT PROCESSING 1. The device issues an interrupt signal to the processor. 2. The processor finishes execution of the current instruction before responding to the interrupt. 3. The processor tests for a pending interrupt request, determines that there is one, and sends an acknowledgment signal to the device that issued the interrupt. • The acknowledgment allows the device to remove its interrupt signal. 4. The processor next needs to prepare to transfer control to the interrupt routine. 5. The processor then loads the program counter with the entry location of the interrupt-handling routine that will respond to this interrupt. 6. At this point, the program counter and PSW relating to the interrupted program have been saved on the control stack. 7. The interrupt handler may now proceed to process the interrupt. 8. The saved register values are retrieved from the stack and restored to the registers 9. The final act is to restore the PSW and program counter values from the stack. 59
MEMORY HIERARCHY Major constraints in memory Amount (capacity) Speed (access time) Expense(cost) Faster access time, greater cost per bit Greater capacity, smaller cost per bit Greater capacity, slower access speed
THE MEMORY HIERARCHY Going down the hierarchy Decreasing cost per bit Increasing capacity Increasing access time Decreasing frequency of access to the memory by the processor Thus, smaller, more expensive, faster memories are supplemented by larger, cheaper, slower memories.
COMPUTER HARDWARE REVIEW Typical memory hierarchy 62
BUSES The system has eight buses Cache Local Memory ISA ( industry standard architecture)(16. 67 MB/sec) PCI ( peripheral component interconnect)( 528 MB/sec) SCSI ( small computer system interface) USB ( universal serial buses) IDE(Integrated Drive Electronics ) 63
COMPUTER HARDWARE REVIEW 64 Structure of a large Pentium system
HOW OPERATING SYSTEM BOOT? BIOS (Basic input output system) It contains the low level I/O Software. When computer is turn on , BIOS are booted. It first check to see how much RAM is installed And whether keyboard and other basic device are installed and responding correctly. The BIOS determines the boot devices by trying a list of devices stored in the BIOS memory. The user can change the list of BOOTING devices by entering a BIOS programming just after booting. If System booted from Hard disk. The first sector of boot device read in to memory and executed. This sector contains partition information and active partition. 65
CONT. Then secondary boot loader is read from partition. The loader reads in the OS from the active partition and start it. The OS then queries the BIOS to get the configuration information. For each device it check to see if it has device driver, if not, it ask to user to insert CD for driver. Then OS load driver in to kernel. It initialize tables, create what ever back ground process are needed. 66
SYSTEM CALL The interface between the operating system and the user program is defined by the set of services provided by the OS. Such as a reading a data from keyboard or file. It has execute a trap or system call instruction to transfer control to the OS. Count = read(fd, buffer, nbytes), 67
STEPS IN MAKING A SYSTEM CALL There are 11 steps in making the system call count = read (fd, buffer, nbytes) 68
SOME SYSTEM CALLS FOR PROCESS MANAGEMENT 69
SOME SYSTEM CALLS FOR FILE MANAGEMENT 70
SOME SYSTEM CALLS FOR DIRECTORY MANAGEMENT 71
SOME SYSTEM CALLS FOR MISCELLANEOUS TASKS 72
SYSTEM CALLS Some Win 32 API calls 73
OPERATING SYSTEM STRUCTURE 1) 2) 3) Monolithic System: A main program that invokes the requested service procedure. A set of service procedures that carry out system calls. A set of utility procedure that help the service procedure. 74
OPERATING SYSTEM STRUCTURE Simple structuring model for a monolithic system 75
LAYERED SYSTEM Structure of the THE operating system 76
MICROKERNEL A microkernel is a small OS core that provides the foundation for modular extensions. only absolutely essential core OS functions should be in the kernel. Ø IPC, Address Space Management, Basic Scheduling. Less essential services and applications are built on the microkernel and execute in user mode. Ø File management, Device Driver, Virtual Management, Process Management. Memory
KERNEL ARCHITECTURE
MICROKERNEL FUNCTION The microkernel functions as a message exchange: • It validates messages, • passes them between components, • and grants access to hardware. 79
CLIENT SERVER MODEL Moving large part of the operating system in to higher level. Minimize the kernel code. This is called a microkernel. Implement most of the OS part in user process. Implement client and server for communication. Client send the request to server using message and kernel handle the communication. Such as file server, process server, Memory server etc…. . Each part become small and manageable. Advantage: Prepare a distributed system Not whole machine down if any one server crash. 80
OPERATING SYSTEM STRUCTURE The client-server model 81
VIRTUAL MACHINE The first version, released in 1972 by IBM, was VM/370, or officially Virtual Machine Facility/370. The heart of the system is virtual machine monitor. VMi 370 has two main components-(CP/CMS)the control program (CP) and the Conversational Monitor System (CMS). It runs on the bare hardware and does the multiprogramming. This providing not one, but several virtual machine on next layer up. This VM are exact copy of the bare hardware, including kernel/user mode, I/O, interrupts and everything else the real machine has. Each VM can run any process. 82
VIRTUAL MACHINE Structure of VM/370 with CMS 83
VIRTUAL MACHINES (CONT. ) Non-virtual Machine Virtual Machine (a) Nonvirtual machine (b) virtual machine
OPERATING SYSTEM STRUCTURE ( The client-server model in a distributed system 85
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