L9-DiskIO - Disk I/O CSIS0230A Lecture Nine Concepts Disk...

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Disk I/O CSIS0230A Lecture Nine Concepts Disk scheduling
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Recommended Reading Chapter 12 of Operating Systems, 3rd edition by Deitel et. al Except 12.10 2 CSIS0230A Principles of Operating Systems
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References Chapter 12 of Operating Systems, 3rd edition by Deitel et. al Chapter 12 and Section 13.2 of Operating System Principles, 7th edition by Silberschatz et. Al Chapter 11 of Operating Systems Internals and Design Principles, 6th edition by W. Stallings 3 CSIS0230A Principles of Operating Systems
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I/O Structure I/O devices and the CPU can execute concurrently Each device controller is in charge of a particular device type OS usually has a device driver for each device controller Each device controller has a local buffer and a set of special hardware registers CPU moves data from/to main memory to/from local buffers I/O is from the device to local buffer of controller 4 CSIS0230A Principles of Operating Systems
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I/O Operations Giving commands to I/O devices Device driver loads the commands to the appropriate registers within the device controller Data movement between main memory and I/O devices Inform the Processor on I/O completion 5 CSIS0230A Principles of Operating Systems
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Giving commands Special I/O instruction specify the transfer of a byte or word to an I/O port address. The I/O instruction triggers bus lines to select the proper device and to move bits into and out of a device register. Memory-Mapped I/O The device-control registers are mapped into the memory address space of the processor CPU executes I/O requests using standard read and write to the mapped memory addresses No special commands for I/O 6 CSIS0230A Principles of Operating Systems
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Direct Memory Access (DMA) tells I/O controller to transfer x bytes from disk to buffer at address Y DMA controller Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention Relieves the processor responsibility for the exchange Used for high-speed I/O devices able to transmit information at close to memory speeds. 7 CSIS0230A Principles of Operating Systems
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I/O Completion Interrupt Processor is interrupted when I/O is completed Processor saves current process context and begins executing interrupt-handler No needless waiting of the I/O completion Processor can do other useful computation 8 CSIS0230A Principles of Operating Systems
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