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22 storage devices


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  • 1. Storage DevicesLecture 22Zikria Mian
  • 2. What is Storage• Storage holds data, instructions andinformation for future use.– All the programs when started are loadedfrom a storage device onto computer memory– Users store a variety of data on mainframes,servers, desktops, notebooks, handhelddevices, smart phones etc
  • 3. Storage Medium• A storage medium is the physical materialon which a computer keeps data,instructions and information.– Hard disks, CDs, DVDs, memory cards, USBflash drives etc are all storage mediums orsecondary storage devices– Storage capacity is the number of bytes astorage medium can hold
  • 4. Storage terms• 1 KB = 210Bytes = 1,024 bytes• 1 MB = 220Bytes = 1,048,576 bytes• 1 GB = 230Bytes = 1,073,741,824 bytes• 1 TB = 240Bytes = 1,099,511,627,776 bytes– A storage medium is non-volatile, that is, itemson storage medium remain intact even whenpower is removed
  • 5. Storage device• A storage device is the computerhardware that records and/or retrievesitems to and from the storage media.– Writing is the process of transferring data,instructions and information from memory tostorage medium.– Reading is the process of transferring theseitems from a storage medium into memory.
  • 6. – When storage devices write data onto storagemedium, they are generating computer output– When storage devices read from storagemedia, they are generating input for thecomputer.* however, storage devices are not categorisedinto input or output devices
  • 7. Speed• The speed of storage devices andmemory is defined by access time.– The time required to locate an item on astorage medium– The time required to deliver an item frommemory to the processor• Access time of storage devices is slow ascompared to memory devices
  • 8. Memory Most RAMStorageHard DiskFlash Memory cardsand USB drivesCDs, DVDs etc
  • 9. Magnetic Disks• Magnetic disks use magnetic particles tostore items on a disk’s surface– Each particle on the magnetic disk representsa bit– Formatting is process of dividing the disk intotracks, sectors and clusters (allocation unit)
  • 10. Hard Disk• A hard disk is a storage device that contains one or moreinflexible magnetic disks
  • 11. • The magnetic disks in a hard disk rotate ata speed from 5,000 to 15,000 rpm• The data transfer rate of hard disks rangefrom 15 mbps to 320 mbps• Hard disks improve their access time byusing disk caching– Disk cache is a memory chip on hard disk thatstores frequently accessed items
  • 12. • A group of two or more integrated harddisks is called RAID (Redundant Array ofIndependent Disks)• Miniature hard disks are present in digitalcameras, portable media players, smartphones etc• A pocket hard drive or portable hard drivealso has a miniature hard disk• External or removable hard disks
  • 13. Hard Disk Controller• A disk controller consists of a special-purpose chip and electronic circuits thatcontrol the transfer of data.– An interface is required by the hard diskcontroller to transfer data to and from the harddisk• SATA (Serial Advanced Technology Attachment)• EIDE (Enhanced Integrated Drive Electronics)• SCSI Interfaces• SAS (Serial Attached SCSI)
  • 14. Online storage• Online storage is a service provided onthe web that gives hard disk storage tousers for free or for a nominal monthly fee– To access data from other computers– To store files like audio, video and graphicson the internet instead of downloading ontolocal hard disk– To allow others to access your files– To store backups
  • 15. Other storage media• Floppy disks : A flexible plastic film with amagnetic coating• Optical discs: A storage media thatconsists of portable disc made of metal,plastic and lacquer that is written and readby a laser– Read/write feature– Double-sided discs
  • 16. Disc type FeaturesCD-ROM Read onlyCD-R Read and writeCD-RW Read, write anderaseDVD-ROM, BD-ROM, HD DVD-ROMRead onlyDVD-R, BD-R, HD DVD-R Read and writeDVD-RW, DVD-RAM, BD-RE, HDDVD-RWRead, write anderase
  • 17. • PC cards and Express cards (developedby Personal Computer Memory CardInternational Association)• Flash memory cards (solid state media)– Secure Digital (SD)– Mini SD– USB flash drives– Smart card (sim, visa card, master card etc)– Enterprise storage