1. Chapter 1: Introduction

2. 1.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Chapter 1: Introduction What Operating Systems Do Computer-System Organization and Architecture Interrupts and I/O Storage Structure

3. 1.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Objectives To provide a grand tour of the major operating systems components To provide coverage of basic computer system organization

4. 1.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts What is an Operating System? A program that acts as an intermediary between a user of a computer and the computer hardware. Operating system goals: Execute user programs and make solving user problems easier. Make the computer system convenient to use. Use the computer hardware in an efficient manner.

5. 1.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts 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

6. 1.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Operating System Definition (Cont.) No universally accepted definition “Everything a vendor ships when you order an operating system” is good approximation But varies wildly “The one program running at all times on the computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program

7. 1.7 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts 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 Application programs – define the ways in which the system resources are used to solve the computing problems of the users  Word processors, compilers, web browsers, database systems, video games Users  People, machines, other computers

8. 1.8 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Four Components of a Computer System

9. 1.9 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Computer System Organization Computer-system operation One or more CPUs, device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs and devices competing for memory cycles

10. 1.10 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Computer-System Operation I/O devices and the CPU can execute concurrently. Each device controller is in charge of a particular device type. Each device controller has a local buffer. CPU moves data from/to main memory to/from local buffers I/O is from the device to local buffer of controller. Device controller informs CPU that it has finished its operation by causing an interrupt.

11. 1.11 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Interrupts An operating system is interrupt driven. An interrupt is an event caused by hardware (I/O, CPU error, power failure, timer, …) or software (trap instructions) CPU will not response the interrupt until the current instruction is completed There is an interrupt enable flag (IF) which can set or reset by instructions. If IF=0, then CPU will not response to any coming interrupt(s).

12. 1.12 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Interrupt Handling The preserves the state of the CPU by storing contents of the registers and the program counter. Determines which type of interrupt has occurred: polling vectored interrupt system Determine necessary action should be taken for each type of interrupt

13. 1.13 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts I/O Structure There are two kinds of I/Os: Non direct memory access (DMA) I/Os: key board, mouse, all USB connected devices. DMA I/Os: hard disk, CD ROM, monitor All I/Os are controlled by the operating system through the system calls. CPU and I/O work simultaneously (currently). When a non-DMA I/O inputs (outputs) a data (byte or word), It sets an interrupt request to inform CPU.

14. 1.14 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Direct Memory Access (DMA) I/O Used for high-speed I/O devices able to transmit information at close to memory speeds. Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention. Only on interrupt is generated per block, rather than the one interrupt per byte.

15. 1.15 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Storage Structure Registers and main memory that the CPU can access directly. Cache is a small memory as a bridge between registers and main memory to store most important instructions and data. Secondary storage – extension of main memory that provides large nonvolatile storage capacity.

16. 1.16 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Storage-Device Hierarchy

17. 1.17 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Caching Faster storage (cache) checked first to determine if information is there If it is, information used directly from the cache (fast) If not, data copied to cache and used there Cache smaller than storage being cached Cache management important design problem Cache size and replacement policy

18. 1.18 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts Performance of Various Levels of Storage Movement between levels of storage hierarchy can be explicit or implicit