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STORAGE DEVICES Introduction Comparision Storage Hierarchy

STORAGE DEVICES Introduction Comparision Storage Hierarchy. Memory vs. Storage. RAM – memory. Hard Drive – storage. Storage , also known as mass media or auxiliary storage , refers to the various media on which a computer system can store data.

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STORAGE DEVICES Introduction Comparision Storage Hierarchy

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  1. STORAGE DEVICES • Introduction • Comparision • Storage Hierarchy

  2. Memory vs. Storage RAM – memory Hard Drive – storage • Storage, also known as mass media or auxiliary storage, refers to the various media on which a computer system can store data. • Storage devices hold programs and data in units called files. • Memory is a temporary workplace where the computer transfers the contents of a file while it is being used.

  3. Why Is Storage Necessary? • Storage devices: • Retain data when the computer is turned off • Are cheaper than memory • Play an important role during startup • Are needed for output

  4. Storage Devices • Storage devices are categorized by: • The type of operations they perform • The method they use to access the information • The technology they use • Their location in the storage hierarchy • Their capacity and speed

  5. Sequential vs. Random Access Storage Hard Disk – random-access storage Tape Drive – sequential storage Floppy Disk Drive – random-access storage • Sequential – Storage devices that read and write data in a serial (one after the other) fashion • Random-Access – Storage devices that read and write data without going through a sequence of locations

  6. Storage Technologies: Magnetic and Optical Optical Storage – CD/DVD drive Magnetic Storage • Magnetic – Storage devices use disks or tapes that are coated with magnetically sensitive material • Optical – Storage devices that use laser beams to read patterns etched into plastic disks

  7. The Storage Hierarchy • The three levels of storage hierarchy are: • Online storage – Also called primary storage, it is made up of the storage devices that are actively available to the computer system. User action is not required. • Near-online storage – Also called secondary storage, it is not readily available to the computer system. The user performs an action, such as inserting a disk, to make it available. • Offline storage – Also called tertiary storage or archival storage, it is not readily available to the computer system. Devices such as tape backup units store data for archival purposes.

  8. Storage Capacity and Speed Floppy Disk Hard Drive CD ROM / DVD • A storage device’s performance is measured by: • Capacity – The number of bytes of data that a device can hold • Access Time – The amount of time, in milliseconds (ms), it takes the device to begin reading data Capacity – CD-ROM 650 MB; DVD 17 GB Access Time – 80 to 800ms Capacity – 720 KB to 1.44 MB Access Time –100ms Capacity – Up to 80 GB Access Time – 6 to 12ms

  9. Hard Disks Platter Read/Write head • Hard disks are high-speed, high-capacity storage devices. • They contain metal disks called platters. • They contain two or more stacked platters with read/write heads for each side. • Hard disks can be divided into partitions to enable computers to work with more than one operating system.

  10. Factors Affecting a Hard Disk’s Performance • Seek time or positioning performance – How quickly the read/write head positions itself and begins transferring information. It is measured in milliseconds (ms). • Spindle speed or transfer performance – How quickly the drive transfers data. It is measured in rotations per minute (RPM).

  11. Floppy and Zip Disks and Drives Zip Drive Floppy Drive Click on the picture to see it work. • A disk or diskette is a portable storage medium. • High-density floppy disks that are commonly used today store 1.44 MB of data. • Disks work with a disk drive. • Zip disks store up to 750 MB of data and are not downwardly compatible with floppy disks. Floppy Disk

  12. CD-ROM Discs and Drives • CD-ROM stands for Compact Disc-Read Only Memory. • CD-ROM drives can not write data to discs. • They are capable of storing 650 MB of data. • They are used for storing operating systems, large application programs, and multimedia programs.

  13. CD-R Discs can be read and written to Discs can only be written to “once” CD-R drives are capable of reading and writing data CD-RW Discs can be read and written to Discs are erasable Discs can be written to many times CD-RW drives are capable of reading, writing, and erasing data CD-R and CD-RW Discs and Recorders

  14. DVD-ROM Discs and Drives • DVD stands for Digital Video Disc. • DVD technology is similar to CD-ROM technology. • DVDs are capable of storing up to 17GB of data. • The data transfer rate of DVD drives is comparable to that of hard disk drives. • DVD-R and DVD-RW drives have the ability to read/write data.

  15. Solid State Storage Devices • Solid state storage devices use nonvolatile memory chips to retain data. • They do not have moving parts. • They are small, lightweight, reliable, and portable.

  16. Solid State Storage Devices Smart Card Memory Stick Compact Flash Memory Flash Memory PC Card Micro Drive

  17. Chapter 5 Summary • Input is the software, data, and information that is entered into the computer’s memory. • Input devices such as the keyboard, mouse, and trackball enable the user to enter data. • A pointing device enables the user to control movements of an on-screen pointer. • Speech recognition software enables the user to enter data into a computer by speaking into a microphone. • Video and images can be entered into a computer by way of digital cameras, scanners, and fax modems. • Monitors enable the user to view the computer’s processed data. The output is known as soft copy.

  18. Chapter 5 Summary (continued) • The two types of monitors are the CRT and the LCD. • A monitor’s quality is measured by screen size, resolution, and refresh rate. • Printers produce permanent versions (hard copies) of the computer’s output. • The two basic types of printers are the inkjet and laser. • Memory makes software and data available for the CPU’s use. • Storage devices are categorized by: Data access (sequential or random-access) Technology (magnetic, optical, or solid state) Hierarchy (online, near-online, or offline) Operations (read-only or read/write)

  19. Chapter 5 Summary (continued) • A hard disk’s performance is measured by its positioning performance and transfer rate. • Optical storage devices include: CD-ROM– Read-only CD-R– Record once CD-RW– Erasable, write repeatedly DVD-ROM– Read-only DVD-R– Read/write • Solid state storage devices include: PC cards Flash memory cards Smart cards

  20. Thanks....................

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