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Discovering Computers Chapter 7 Storage

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2 Ch 4 Processor Control Unit Arithmetic Logic Unit (ALU) Input Devices Ch 5 Storage Devices Ch 7 Output Devices Ch 6 Memory DataInstructions Information Instructions Data Information Instructions Data Information Control Unit Ch 1 Introduction Ch 2 Internet & WWW Ch 3 Application Software Ch 8 System Software

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Writing Transfers items from memory to storage media Writing Transfers items from memory to storage media What a storage device does? Reading Transfers items from storage media to memory Reading Transfers items from storage media to memory Hardware that writes writes records to the medium holds them and reads from 4

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5 Reading is the process of transferring items from a storage medium into memory Writing is the process of transferring items from memory to a storage medium

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6 Storage device and a storage medium storage medium Physical material on which a computer keeps info storage device Hardware that records, holds and retrieves items to and from a storage medium

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7 How does storage differ from memory ? To work with a file, you read a part (a block of records) from storage (block by block) and place it in memory When you are finished with the block of a file, you write it from memory to the storage Stores items for future use, rather than current use Stores for a long time, rather than temporarily Storage is nonvolatile, rather than volatile

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8 How does volatility compare? Contents of storage retained when power is off - nonvolatile Screen display and contents of RAM are volatile erased when power is off Screen display and contents of RAM are volatile erased when power is off

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9 What is capacity? Number of bytes storage medium can hold Storage Term Number of bytes Kilobyte Megabyte Gigabyte Terabyte Petabyte KB MB TB GB PB 1 thousand 1 million 1 billion 1 trillion 1 quadrillion Abbreviation

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Google believes that the plummeting price of storage will allow iPods of the future (2020 A.D. ) to hold any video ever produced.

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Access time: The amount of time it takes a storage device to locate an item on a storage medium 12

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13 Memory (RAM) Flash memory Compact disk Tape Hard Disk cost less expensive more expensive speed faste r slower What is access time? Amount of time it takes device to locate block on disk measured in millisec / microsec / nanosec / picosec

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Floppy DiskSmall files to be transported Secondary Storage Primary Storage Hard Disk Flash Memory Cards and USB Flash Drives CDs and DVDs Tape Items waiting to be interpreted and executed by the processor Operating system, application software, user data and information Digital pictures or files to be transported Software, backups, movies, music Backups Memory (most RAM) What is transfer rate? Time required to deliver a block from storage to memory in kilobytes/sec (KB/sec) or megabytes/sec (MB/sec) faster transfer rates slower transfer rates 14

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Hard disk contains one or more inflexible, circular platters that use magnetic particles to store data, instructions, and information 15

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Characteristics of a hard disk: 17 CapacityPlatters Read/Write Heads Cylinders Sectors and Tracks Revolutions per Minute Transfer Rate Access Time

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Sample: Hard Disk Characteristics Advertised capacity500 GB Platters4 Read/write heads8 Cylinders16,383 Bytes per sector512 Sectors per track63 Sectors per drive973,773,168 Revolutions per minute7,200 Transfer rate300 MB per second Access time8.5 ms 18

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19 Calculating capacity of a hard drive Sector stores 512 bytes of data 16383 cylinders times 8 tracks in a cylinder times 63 sectors per track times 512 bytes per sector = 500 GB

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An external hard disk is a separate free-standing hard disk that connects to your computer with a cable or wirelessly A removable hard disk is a hard disk that you insert and remove from a drive Internal and external hard disks are available in miniature sizes (miniature hard disks) 22

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23 Hard Disk Terminology Platter Track SectorHeadArm Cylinder

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platter read/write head platter sides cylinder track sector 24

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26 Track is the narrow recording band that forms full circle on disk surface Cylinder is the collection of single tracks through all platters Single movement of read/write head arms can read any track on the cylinder track cylinder

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What is a head crash? Spinning creates cushion of air that floats read/write head above platter Occurs when read/write head touches platter surface A smoke particle, dust particle, or human hair could render drive unusable 27

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28 How does RAID work? Redundant Array of Independent Disks Disk system that duplicates data, instructions, and information to improve data reliability mirroring (RAID Level 1) Mirroring has one backup disk for each primary disk

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External hard disk freestanding hard disk that connects to system unit Removable hard disk you insert and remove from hard disk drive 29

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What is a disk cache ? Portion of memory that processor uses to store frequently accessed items second request for data goes to hard disk first request for data goes to disk cache 30

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31 Disk History 1973: 140 MB 1979: 2,300 Mbytes = 2.3 GB

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32 1 inch disk drive! v Hitachi 2007 release Development driven by iPods & digital cameras 20GB, 5-10MB/s

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Flash Memory Storage Flash memory chips contain no moving parts solid state drives; they have several advantages over magnetic hard disks: 33 Faster access time Faster transfer rates Generate less heat and consume less power Last longer

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USB flash drives plug into a USB port on a computer or mobile device 34

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A memory card is a removable flash memory that you insert and remove from a slot in a computer 36 CompactFlash (CF) Secure Digital (SD) Secure Digital High Capacity (SDHC) microSDmicroSDHC xD Picture Card Memory Stick Memory Stick Micro (M2)

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What are PC Cards? Add capabilities to computer Credit-card-sized device commonly used in notebook computers 38

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What is a smart card? Stores data on microprocessor embedded in small card Input, process, output, and storage capabilities 39

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Cloud Storage 40

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41 Security Allows offsite backups of data Share Others can be authorized to access data from your Internet hard drive Accessibility Files can be accessed from any computer or device with Web access When in need Large audio, video, and graphics files can be downloaded to an Internet hard drive What are advantages of an Internet storage?

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Reasons to subscribe to cloud storage: 42 Access files from any computerStore large filesAllow others to access their filesView data and imagesStore offsite backupsProvide data center functions

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Push the same button to close the tray. What are optical discs? Most PCs include an optical disc drive Flat, round, portable discs made of metal or plastic Can be read only or read/write Insert the disc, label side up. Push the button to slide out the tray. 43

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How does a laser read data on an optical disc? laser diode prism light- sensing diode 01 lens pitland disc label Step 1. Laser diode shines a light beam toward disc. Step 2. If light strikes a pit, it scatters. If light strikes a land, it is reflected back toward diode. Step 3. Reflected light sends digital signals of 1 to computer. Absence of reflected light is read as digital signal of 0. 44

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How is data stored on an optical disc? Data is stored in single track Track divided into evenly sized sectors that store items single track spirals to edge of disc disc sectors 45

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How should you care for an optical disc? 46

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What is the data transfer rate of a CD drive? Ranges from 48X to 75X 75X 75 150 KBps = 11,250 KBps or 12.25 MBps X is 150 KBps (KB per second ) 48X: 48 150 KBps = 7,200 KBps or 7.2 MBps 47

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A CD-ROM can be read from but not written to A CD-R is an optical disc on which users can write, but not erase A CD-RW is an erasable disc 48

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What is a CD-ROM? Compact disc read-only memory Cannot erase or modify contents Typically holds 650 MB to 1 GB Commonly used to distribute multimedia and software 49

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What are CD-Rs and CD-RWs? Must have CD recorder or CD-R drive Cannot erase discs contents CD-R (compact disc-recordable) you can write on once CD-RW (compact disc-rewritable) disc you can write on multiple times Must have CD-RW software and CD-RW drive 50

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What is a DVD-ROM (digital video disc-ROM)? Must have DVD-ROM drive or DVD player to read DVD-ROM Stores databases, music, complex software, and movies Blu-Ray discs have storage capacity of up to 100 GB HD-DVD discs have storage capacity of up to 60 GB 51

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Other Types of Storage 52

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What is a tape? Magnetically coated plastic ribbon capable of storing large amounts of data at low cost Used for backup 53

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54 What is sequential access versus direct access? sequential access Reading and writing data consecutively Method used for tape direct access You can locate a particular data item or file immediately Method used for hard disks, and compact discs Also called random access

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How is data stored on a tape? Sequential access Unlike direct access ( used on hard disks, CDs, and DVDs ) which can locate particular item much faster Reads and writes data consecutively, like music tape 55

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A magnetic stripe card contains a magnetic stripe that stores information A smart card stores data on a microprocessor embedded in the card 56

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Microfilm and Microfiche Images are recorded using computer output microfilm recorder Store microscopic images of documents on roll or sheet of film Microfilm 100- to 215-foot roll of film Microfiche small sheet of film, usually 4 6 57

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Enterprise storage stores huge volumes of data and information for large businesses Uses special hardware for heavy use, maximum availability, and maximum efficiency 59

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