18-Mass_Storage_ and_IO_I-2spp

18-Mass_Storage_ and_IO_I-2spp - CSC 4103 - Operating...

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1 CSC 4103 - Operating Systems Spring 2007 Tevfik Ko ş ar Louisiana State University March 29 th , 2007 Lecture - XVIII Storage and I/O - I Overview of Mass Storage Structure Magnetic disks provide bulk of secondary storage of modern computers Drives rotate at 60 to 200 times per second Transfer rate is rate at which data flow between drive and computer Seek time: time to move disk arm to desired cylinder Rotational latency: time for desired sector to rotate under the disk head Positioning time ( random-access time ): seek time + rotational latency Head crash results from disk head making contact with the disk surface • That’s bad Disks can be removable Drive attached to computer via I/O bus Busses vary, including EIDE, ATA, SATA, USB, Fibre Channel, SCSI Host controller in computer uses bus to talk to disk controller built into drive or storage array
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Moving-head Disk Mechanism Overview of Mass Storage Structure (Cont.) • Magnetic tape Was early secondary-storage medium Relatively permanent and holds large quantities of data Access time slow Random access ~1000 times slower than disk Mainly used for backup, storage of infrequently-used data, transfer medium between systems
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18-Mass_Storage_ and_IO_I-2spp - CSC 4103 - Operating...

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