Chapter 1: Introduction

1. Chapter 1: Introduction

2. Chapter 1: Introduction • What Operating Systems Do • Computer-System Organization • Operating-System Structure • Operating-System Operations • Process Management • Memory Management • Storage Management • Protection and Security

3. Distributed Systems • Real-Time/Embedded Systems

4. Objectives • To provide an overview of the major operating systems components • To review basic computer system organization

5. What is an Operating System? • A program that acts as an intermediary between a user and hardware • Operating system goals: • Execute user programs and make solving user problems easier • Make the computer system convenient to use • Use the computer hardware efficiently

6. Computer System Structure • Computer system can be divided into four components • Hardware – provides basic computing resources • CPU, memory, I/O devices • Operating system • Controls and coordinates use of hardware among various applications and users

7. Application programs • Word processors, compilers, web browsers, database systems, video games • Users/clients • People, machines, other computers

8. Four Components of a Computer System

9. Operating System Definition • OS is a resource allocator • Manages all resources • Decides between conflicting requests for efficient and fair resource use • OS is a control program • Controls execution of programs to prevent errors and improper use of the computer • Kernel: Core of OS

10. Computer Startup • bootstrap program is loaded at power-up or reboot • Firmware stored in ROM or EPROM • Initializates the system • Loads operating system kernel and starts execution

11. Computer System Organization • CPU(s) & device controllers connect through common bus providing access to main memory

12. Storage-Device Hierarchy Faster More Expensive

13. Caching • Data temporally copied from slower to faster storage • Check cache first • Cache < Storage being cached • How to determine appropriate cache size • Replacement policy • Cache coherency in multiprocessor environment

14. SRAM • Stores a bit in a flip-flop • Two cross connected NAND or NOR gates • Stores a bit as long as power is applied • Consumes less power than DRAM but more complex circuitry • Generally requires 6 transistors • More expensive

15. DRAM • One transistor + Capacitor • Electrical charge on capacitor leaks over time • Periodically refresh • Slower than SRAM • Consumes more power • Cheaper than SRAM • Simpler circuitry

16. Operating System Structure • Multiprogramming • Efficient resource usage • Single user cannot keep CPU and I/O devices busy at all times • Organizes jobs so that CPU always has one to execute • A subset of total jobs in system is kept in memory • When a job blocks, e.g., for I/O, OS switches to another job

17. Timesharing/Multitasking • CPU switches jobs very frequently • Users can interact with each job while it is running, creating interactive computing • Response time should be < 1 second • Each user has at least one program executing in memory process • If several jobs ready to run at the same time  CPU scheduling • If processes don’t fit in memory, swapping moves them in and out to run • Virtual memory allows execution of processes not completely in memory

18. Memory Layout for Multiprogrammed System

19. Operating System Operations • Hardware Interrupts • Software error or request creates exception or trap • Division by zero • Other problems: infinite loop, processes modifying each other or OS • Accounting & resource management • Protection

20. Basic Protection • Dual-mode operation • User mode & kernel mode • Mode bit • Distinguish whether system is running user code or kernel code • Privileged instructions only executable in kernel mode • System call • Change to kernel mode • Process the system call • Return the result • Switch back to user mode

21. Process Management • A process is a program in execution • Unit of work • Single- or multi-threaded • Resource allocation • Process needs resources to accomplish its task • CPU, memory, I/O, files, data • Resources reclamation at process termination • Program counter indicates the location • Multiple processes can run concurrently on one or more CPUs • Concurrency by multiplexing the CPUs among the processes / threads

22. Process Management Activities • Create and delete both user and system processes • Suspend and resume processes • Provide mechanisms for process synchronization • Provide mechanisms for process communication • Provide mechanisms for deadlock handling

23. Memory Management • Instruction and data need to be in main memory to be processed • Keep track of which parts of memory are currently used and by whom • Decide which processes and data to move into and out of memory • Allocate and deallocate memory space as needed

24. Mass Storage Management • Performance bottleneck • Orders of magnitude performance difference between main memory & secondary storage • OS activities • Free space management • Storage allocation • Disk scheduling • Some storage need not be fast • Tertiary storage includes optical storage, magnetic tape • Still must be managed • Varies between WORM (write-once, read-many-times) and RW (read-write)

25. I/O Subsystem • Hide peculiarities of hardware devices from the user • I/O subsystem responsible for • Buffering: store data temporarily while it is being transferred • Caching: store parts of data in faster storage • Spooling (Simultaneous Peripheral Operations On-Line) • Put data in a designated buffer • I/O device can pull the data at its own rate • Print spooling can let a user do something else while printing and request several prints without waiting for one print request to finish • Device-driver interfaces

26. Two I/O Methods Synchronous Asynchronous • Synchronous I/O • Application is blocked until the I/O finishes • Only one I/O device is active • Easy to determine which device needs service • No concurrent I/O possible

27. I/O Interrupts • Extract interrupt service vector • Look up interrupt service table • Save the current process status such as the register values and address of the interrupted instruction • Disable interrupt if necessary • Transfer control to the interrupt service routine

28. Interrupt Timeline

29. Direct Memory Access Structure • Used for high-speed I/O devices able to transmit information at close to memory speed • Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention • Only one interrupt is generated per block, rather than one interrupt per byte • Cycle stealing

30. Device-Status Table

31. Computer system architecture • Single processor systems • Multiprocessor systems • Multiple CPUs sharing main memory • Objectives • Increase throughput • Fault tolerance • Asymmetric multiprocessing • A master processor controls the system • Symmetric multiprocessing (SMP) • All processors are peers • No master-slave relation

32. Multiprocessor systems (continued) • Multicore CPU • Essentially multiprocessors on a single chip • Faster communications between processors • Uses much less power than multiple single-core chips • Good for servers such as web/database servers

33. Clustered systems • A cluster consists of two or more individual systems unlike multiprocessor systems • Clustered computers share storage and linked by a local area network, e.g., Ethernet or InfiniBand • To support fault tolerance and high performance, for example, in a web server farm • Distributed systems

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