Interrupt Request Lines IRQ Physical input to the interrupt controller chip

Interrupt request lines irq physical input to the

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Each controller is assigned a special address called a port. Interrupt Request Lines (IRQ) » Physical input to the interrupt controller chip » Signals when the device controller is ready to have its registers read/written via the I/O Ports (addresses) assigned that controller. 6 I/O Ports and IRQs 47 54 41 40 MINIX Interrupt Vector 15 7 378-37F Printer 118 14 1F0-1F7 Hard Disk 9 1 060-063 Keyboard 8 0 040-043 Clock DOS Interrupt Vector Hardware IRQ I/O address I/O Controller Example: PC with MS-DOS
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7 Direct Memory Access (DMA) Used mainly for block devices 8 Anatomy of a Disk Basic components 0 1 2 s –1 .. . Block/Sector Track Cylinder Platter Surface Head Spindle
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9 Anatomy of a Disk Example: Seagate 9GB Fast/Wide/Differential SCSI disk Specs: » 12 platters » 22 heads » variable # of sectors/track » 7,200 RPM average latency: 4.2 ms. » Seek times track-to-track: 1 ms average: 7.9 ms » 40MB/s peak transfer rate » 11 arms » 4,735 tracks » 512 bytes/sector 10 Present disk with a sector address » DA = ( drive , surface , track , sector ) Head moved to appropriate track » “seek time” The appropriate head is enabled Wait for the sector to appear under the head » “rotational latency” Read/write the sector » “transfer time” Random access devices with non-uniform access times Disk Operations Data transfer in units of sectors
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11 Disk Interleaving Blocks are often placed on the disk in non- sequential order to allow time for the DMA buffer to be transferred to main memory.
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  • Input/output, Interrupt request

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