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Operating Systems Lecture #4: IO Management WrittenbyDavidGoodwin basedonthelectureseriesofDr. DayouLi andthebookUnderstandingOperatingSystems4thed. byI.M.FlynnandA.McIverMcHoes (2006) DepartmentofComputerScienceandTechnology, UniversityofBedfordshire. OperatingSystems,2013 18th February 2013 Outline Lecture#4IO Management 1 Device types DavidGoodwin Universityof 2 DASD Bedfordshire 3 Components of IO subsystem Devicetypes DASD 4 Communication ComponentsofIO Polling & Interrupts subsystem Communication DMA Polling&Interrupts Buffers DMA Buffers 5 Management of IO requests ManagementofIO requests 6 Device Handling Algorithms DeviceHandling FCFS Algorithms FCFS SSTF SSTF SCAN SCAN RAID 7 RAID summary 8 summary OperatingSystems 52 Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Devicetypes 3 Device types DASD ComponentsofIO subsystem Communication Polling&Interrupts DMA Buffers ManagementofIO requests DeviceHandling Algorithms FCFS SSTF SCAN RAID summary OperatingSystems 52 I/O HARDWARE Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Devicetypes 4 (cid:136) Incredible variety of I/O devices DASD (cid:136) Common concepts ComponentsofIO subsystem (cid:136) Port Communication (cid:136) Bus (daisy chain or shared direct access) Polling&Interrupts (cid:136) Controller (host adapter) DMA Buffers (cid:136) I/O instructions control devices ManagementofIO (cid:136) Devices have addresses, used by requests DeviceHandling (cid:136) Memory-mapped I/O Algorithms (cid:136) Direct I/O instructions FCFS SSTF SCAN RAID summary OperatingSystems 52 TYPES OF DEVICES Lecture#4IO Management DavidGoodwin Universityof Bedfordshire (cid:136) Dedicated Devicetypes 5 (cid:136) Assigned to only one job at a time, e.g. printers, tape drives, DASD etc. ComponentsofIO (cid:136) Shared subsystem Communication (cid:136) Can be assigned to several processes, e.g. a disk can be Polling&Interrupts shared by several processes at the same time by interleaving DMA their requests which are carefully controlled by the Device Buffers Manager. ManagementofIO requests (cid:136) Virtual DeviceHandling Algorithms (cid:136) A combination of the first two –dedicated devices transferred FCFS to shared devices, e.g. a printer made sharable through SSTF spooling (Simultaneous Peripheral Operation On-Line). SCAN RAID summary OperatingSystems 52 STORAGE DEVICES Lecture#4IO Management DavidGoodwin (cid:136) Sequential access storage Universityof Bedfordshire (cid:136) Paper printout, punch cards, paper tapes, magnetic tapes Devicetypes 6 (cid:136) Direct access storage devices (DASDs) DASD (cid:136) Magnetic disks (fixed-head and moveable-head) ComponentsofIO (cid:136) Optical discs (CD-ROM, CD-Recordable, CD-Rewritable, subsystem DVD) Communication Polling&Interrupts (cid:136) Magneto-optical (combination of magnetic and optical discs) DMA (cid:136) Flash memory Buffers (cid:136) Removable medium that emulates random access memory ManagementofIO requests but unlike RAM, it stores data securely even it is removed DeviceHandling from its power supply Algorithms FCFS (cid:136) RAID (Redundant Array of Inexpensive/independent Disks) SSTF (cid:136) A set of physical disk drives viewed as a single logical unit by SCAN RAID OS to close the widening gap between increasingly fast summary processors and slower disk drives OperatingSystems 52 Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Devicetypes DASD DASD 7 ComponentsofIO subsystem Communication Polling&Interrupts DMA Buffers ManagementofIO requests DeviceHandling Algorithms FCFS SSTF SCAN RAID summary OperatingSystems 52 DASD ACCESS TIMES Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Devicetypes (cid:136) For a fixed-head DASD DASD 8 Total access time(t )= a ComponentsofIO subsystem Sum of search time(ts)+Transfer time(tt) Communication (cid:136) Search time t s Polling&Interrupts Best search time t =0 DMA s Worst search time t =r (r is time taken per revolution of Buffers s disk) ManagementofIO requests r Average search time t = DeviceHandling s 2 Algorithms (cid:136) Transfer time t t FCFS SSTF SCAN RAID summary OperatingSystems 52 DASD ACCESS TIMES Lecture#4IO Management DavidGoodwin Universityof Bedfordshire (cid:136) Example for a fixed-head DASD Devicetypes DASD 9 A complete revolution takes 14ms, and data transfer time is ComponentsofIO 0.16ms per record. Calculate subsystem Communication (cid:136) Total average access time for 20 individual records Polling&Interrupts (cid:136) Total average access time for a block of 20 records DMA (cid:136) Time saving between the two Buffers ManagementofIO (cid:18)14 (cid:19) requests (cid:136) t for 20 individual records =20 +0.16 =143.2ms a 2 DeviceHandling Algorithms 14 (cid:136) t for block of 20 records = +20×0.16=10.2ms FCFS a 2 SSTF (cid:136) Time saving =143.2–10.2=133.0ms SCAN RAID summary OperatingSystems 52 Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Components of IO Devicetypes DASD ComponentsofIO 10 subsystem subsystem Communication Polling&Interrupts DMA Buffers ManagementofIO requests DeviceHandling Algorithms FCFS SSTF SCAN RAID summary OperatingSystems 52

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Operating Systems Lecture #4: IO Management WrittenbyDavidGoodwin basedonthelectureseriesofDr. DayouLi andthebookUnderstandingOperatingSystems4thed. byI.M.FlynnandA.McIverMcHoes (2006) DepartmentofComputerScienceandTechnology, UniversityofBedfordshire. OperatingSystems,2013 18th February 2013 Outline Lecture#4IO Management 1 Device types DavidGoodwin Universityof 2 DASD Bedfordshire 3 Components of IO subsystem Devicetypes DASD 4 Communication ComponentsofIO Polling & Interrupts subsystem Communication DMA Polling&Interrupts Buffers DMA Buffers 5 Management of IO requests ManagementofIO requests 6 Device Handling Algorithms DeviceHandling FCFS Algorithms FCFS SSTF SSTF SCAN SCAN RAID 7 RAID summary 8 summary OperatingSystems 52 Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Devicetypes 3 Device types DASD ComponentsofIO subsystem Communication Polling&Interrupts DMA Buffers ManagementofIO requests DeviceHandling Algorithms FCFS SSTF SCAN RAID summary OperatingSystems 52 I/O HARDWARE Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Devicetypes 4 (cid:136) Incredible variety of I/O devices DASD (cid:136) Common concepts ComponentsofIO subsystem (cid:136) Port Communication (cid:136) Bus (daisy chain or shared direct access) Polling&Interrupts (cid:136) Controller (host adapter) DMA Buffers (cid:136) I/O instructions control devices ManagementofIO (cid:136) Devices have addresses, used by requests DeviceHandling (cid:136) Memory-mapped I/O Algorithms (cid:136) Direct I/O instructions FCFS SSTF SCAN RAID summary OperatingSystems 52 TYPES OF DEVICES Lecture#4IO Management DavidGoodwin Universityof Bedfordshire (cid:136) Dedicated Devicetypes 5 (cid:136) Assigned to only one job at a time, e.g. printers, tape drives, DASD etc. ComponentsofIO (cid:136) Shared subsystem Communication (cid:136) Can be assigned to several processes, e.g. a disk can be Polling&Interrupts shared by several processes at the same time by interleaving DMA their requests which are carefully controlled by the Device Buffers Manager. ManagementofIO requests (cid:136) Virtual DeviceHandling Algorithms (cid:136) A combination of the first two –dedicated devices transferred FCFS to shared devices, e.g. a printer made sharable through SSTF spooling (Simultaneous Peripheral Operation On-Line). SCAN RAID summary OperatingSystems 52 STORAGE DEVICES Lecture#4IO Management DavidGoodwin (cid:136) Sequential access storage Universityof Bedfordshire (cid:136) Paper printout, punch cards, paper tapes, magnetic tapes Devicetypes 6 (cid:136) Direct access storage devices (DASDs) DASD (cid:136) Magnetic disks (fixed-head and moveable-head) ComponentsofIO (cid:136) Optical discs (CD-ROM, CD-Recordable, CD-Rewritable, subsystem DVD) Communication Polling&Interrupts (cid:136) Magneto-optical (combination of magnetic and optical discs) DMA (cid:136) Flash memory Buffers (cid:136) Removable medium that emulates random access memory ManagementofIO requests but unlike RAM, it stores data securely even it is removed DeviceHandling from its power supply Algorithms FCFS (cid:136) RAID (Redundant Array of Inexpensive/independent Disks) SSTF (cid:136) A set of physical disk drives viewed as a single logical unit by SCAN RAID OS to close the widening gap between increasingly fast summary processors and slower disk drives OperatingSystems 52 Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Devicetypes DASD DASD 7 ComponentsofIO subsystem Communication Polling&Interrupts DMA Buffers ManagementofIO requests DeviceHandling Algorithms FCFS SSTF SCAN RAID summary OperatingSystems 52 DASD ACCESS TIMES Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Devicetypes (cid:136) For a fixed-head DASD DASD 8 Total access time(t )= a ComponentsofIO subsystem Sum of search time(ts)+Transfer time(tt) Communication (cid:136) Search time t s Polling&Interrupts Best search time t =0 DMA s Worst search time t =r (r is time taken per revolution of Buffers s disk) ManagementofIO requests r Average search time t = DeviceHandling s 2 Algorithms (cid:136) Transfer time t t FCFS SSTF SCAN RAID summary OperatingSystems 52 DASD ACCESS TIMES Lecture#4IO Management DavidGoodwin Universityof Bedfordshire (cid:136) Example for a fixed-head DASD Devicetypes DASD 9 A complete revolution takes 14ms, and data transfer time is ComponentsofIO 0.16ms per record. Calculate subsystem Communication (cid:136) Total average access time for 20 individual records Polling&Interrupts (cid:136) Total average access time for a block of 20 records DMA (cid:136) Time saving between the two Buffers ManagementofIO (cid:18)14 (cid:19) requests (cid:136) t for 20 individual records =20 +0.16 =143.2ms a 2 DeviceHandling Algorithms 14 (cid:136) t for block of 20 records = +20×0.16=10.2ms FCFS a 2 SSTF (cid:136) Time saving =143.2–10.2=133.0ms SCAN RAID summary OperatingSystems 52 Lecture#4IO Management DavidGoodwin Universityof Bedfordshire Components of IO Devicetypes DASD ComponentsofIO 10 subsystem subsystem Communication Polling&Interrupts DMA Buffers ManagementofIO requests DeviceHandling Algorithms FCFS SSTF SCAN RAID summary OperatingSystems 52

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