Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Chapter 2 Computer-System Structures n Computer System Operation n I/O Structure n Storage Structure n Storage Hierarchy n Hardware Protection n Network Structure

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Computer-System Architecture

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

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Common Functions of Interrupts n Interrupt transfers control to the interrupt service routine through the interrupt vector F Interrupt vector contains the addresses of all the service routines. F Interrupt architecture must save the address of the interrupted instruction. n Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt. n A trap is a software-generated interrupt caused either by an error or a user request.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Interrupt Handling n The operating system preserves the state of the CPU by storing registers and the program counter. n Also determines which type of interrupt has occurred: F polling F vectored interrupt system n Separate segments of code determine what action should be taken for each type of interrupt

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Interrupt Time Line For a Single Process Doing Output

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Chapter 2 Computer-System Structures n Computer System Operation n I/O Structure F I/O Interrupts F DMA Structure n Storage Structure n Storage Hierarchy n Hardware Protection n Network Structure

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts I/O Structure n Two I/O methods, synchronous and asynchronous n Synchronous I/O: After I/O starts, control returns to user program only upon I/O completion. F Wait instruction idles the CPU until the next interrupt F Wait loop (contention for memory access). F At most one I/O request is outstanding at a time, no simultaneous I/O processing.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts I/O Structure n Asynchronous I/O: After I/O starts, control returns to user program without waiting for I/O completion. F System call – request to the operating system to allow user to wait for I/O completion. F Device-status table contains entry for each I/O device indicating its type, address, and state. F Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Two I/O Methods Synchronous Asynchronous

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Device-Status Table

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

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Chapter 2 Computer-System Structures n Computer System Operation n I/O Structure n Storage Structure F Main Memory F Magnetic Disks F Magnetic Tapes n Storage Hierarchy n Hardware Protection n Network Structure

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Storage Structure n Main memory F the only large storage media that the CPU can access directly. n To allow more convenient access to I/O devices, memory mapped I/O is provided. F Ranges of memory addresses are mapped to device registers. n Ideally we want the programs and data to reside in main memory permanently, but it’s impossible. 4 Main memory is usually too small. 4 Main memory is a volatile storage device 4 Typical solution: Secondary Storage

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Storage Structure n Secondary storage F extension of main memory that provides large nonvolatile storage capacity. n Magnetic disks F Rigid metal or glass platters covered with magnetic recording material F Disk surface is logically divided into tracks, which are subdivided into sectors. F The disk controller determines the logical interaction between the device and the computer.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Storage Structure n Magnetic Tapes F Early secondary storage medium F Relatively permanent and can hold large quantities of data n Disadvantages F Slow access time F Very slow random access n Used mainly for backup, storage of infrequently used data, and as a data transfer medium.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Moving-Head Disk Mechanism

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Chapter 2 Computer-System Structures n Computer System Operation n I/O Structure n Storage Structure n Storage Hierarchy F Caching F Coherency and Consistency n Hardware Protection n Network Structure

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Storage Hierarchy n Storage systems organized in hierarchy. F Speed F Cost F Volatility n Going up in the pyramid, increases speed, cost and volatility.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Storage-Device Hierarchy

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Caching n Caching F Copying information into faster storage system F Main memory can be viewed as a last cache for secondary storage. n Use of high-speed memory to hold recently- accessed data. F Requires a cache management policy. n Caching introduces another level in storage hierarchy. This requires data that is simultaneously stored in more than one level to be consistent.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Coherency and Consistency n Regarding the hierarchical storage structure, the same data may appear in different levels F Requires mechanisms to provide Coherency and Consistency n Coherency: In a multiprocessor environment, every variable value update in one cache must immediately be reflected in all other caches where the variable resides. n Consistency: In a distributed environment, when a replica is updated all other replicas must be updated as soon as possible.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Migration of A From Disk to Register

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Chapter 2 Computer-System Structures n Computer System Operation n I/O Structure n Storage Structure n Storage Hierarchy n Hardware Protection F Dual-Mode Operation F I/O Protection F Memory Protection F CPU Protection n Network Structure

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Dual-Mode Operation n Sharing system resources requires operating system to ensure that an incorrect program cannot cause other programs to execute incorrectly. n Provide hardware support to differentiate between at least two modes of operations. 1.User mode Execution done on behalf of a user. 2.Monitor mode (also kernel mode or system mode) Execution done on behalf of operating system.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Dual-Mode Operation (Cont.) n Mode bit added to computer hardware to indicate the current mode: monitor (0) or user (1). n When an interrupt or fault occurs, hardware switches to monitor mode. Privileged instructions can be issued only in monitor mode. monitoruser Interrupt/fault set user mode

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts I/O Protection n All I/O instructions are privileged instructions. n Must ensure that a user program could never gain control of the computer in monitor mode (i.e., a user program that, as part of its execution, stores a new address in the interrupt vector).

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Use of A System Call to Perform I/O

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Memory Protection n Must provide memory protection at least for the interrupt vector and the interrupt service routines. n In order to have memory protection, add two registers that determine the range of legal addresses a program may access: F Base register 4 Holds the smallest legal physical memory address. F Limit register 4 Contains the size of the range n Memory outside the defined range is protected.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Use of A Base and Limit Register

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Hardware Address Protection

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Memory Protection n When executing in monitor mode, the operating system has unrestricted access to both monitor and user’s memory. n The load instructions for the base and limit registers are privileged instructions.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts CPU Protection n Protecting CPU from getting stuck by a user program F User program may fall in an infinite loop and never return control to the OS. n Timer – interrupts computer after specified period to ensure operating system maintains control. F Timer is decremented every clock tick. F When timer reaches the value 0, an interrupt occurs. n Timer commonly used to implement time sharing. n Timer also used to compute the current time. n Load-timer is a privileged instruction.

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Chapter 2 Computer-System Structures n Computer System Operation n I/O Structure n Storage Structure n Storage Hierarchy n Hardware Protection n Network Structure F Local Area Networks (LAN) F Wide Area Networks (WAN)

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Local Area Network Structure

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Wide Area Network Structure

Thanks to Silberschatz, Galvin and Gagne  Operating System Concepts Exercises n Answer these exercises F 1, 3, 5, 6, 7, 8, 11 n Send your answers in two weeks to the teacher assistant. n Late Policy F You will lose half the score in the case of less than 3 days latency. F You will lose all the score after that.