INTRODUCTION TO Data Storage

Transcription

1 Introduction to Computing INTRODUCTION TO Data Storage CPU AND MICROPROCESSOR Memory Used to store data, instructions, and information The operating system and other system software Application programs Data being processed by application programs Bytes are stored at specific locations or addresses

2 Memory Memory Size of memory is measured by the number of bytes available Memory Memory Volatile memory contents are lost when the computer is powered down Nonvolatile memory contents are not lost when the computer is powered down

3 Memory Random Access Memory (RAM) The memory chips in the system unit When the computer starts, operating system files are loaded from a hard disk into RAM

4 Memory Random Access Memory (RAM) RAM Chips Smaller in size than processor chips Packaged on circuit boards called single inline memory modules (SIMMs) or dual inline memory modules (DIMMs) Memory Random Access Memory (RAM) Configuring RAM The more RAM, the more programs and files a computer can work on at once Software usually tells you how much RAM is required Necessary RAM depends on what type of work the computer is used for

5 Affecting Processing Speed Virtual RAM Computer is out of actual RAM File that emulates RAM Computer swaps data to virtual RAM Least recently used data is moved 5A-30 Memory Nonvolatile memory Holds data when power is off Read Only Memory (ROM) Basic Input Output System (BIOS) Power On Self Test (POST) 5A-31

6 Memory Read-Only Memory (ROM) Cannot be modified Contents not lost when the computer is turned off PROM EPROM EEPROM Bus Address Bus Data Bus Bay

7 Cache Memory Helps speed computer processes by storing frequently used instructions and data Also called memory cache How Computers Process Data Flash memory Data is stored using physical switches Special form of nonvolatile memory Camera cards, USB key chains 5A-35

8 Affecting Processing Speed The bus Electronic pathway between components Expansion bus connects to peripherals System bus connects CPU and RAM Bus width is measured in bits Speed is tied to the clock 5A-36 T e a c h e r s D i s c o v e r i n g C o m p u t e r s Integrating Technology in the Classroom 3 rd Edition Secondary Storage

9 WHAT IS STORAGE? The media on which data, instructions, and information are kept The devices that record and retrieve data, instructions, and information Like a filing cabinet WHAT IS STORAGE? Storage Media and Devices Storage medium Also called secondary storage Physical material Storage device Mechanism used to record and retrieve Capacity measured in megabytes or gigabytes

10 Storage Devices Floppy Disk Hard Disk CD / DVD Miniature Cards Smart Cards Floppy Disks What is a floppy disk drive? Device that reads from and writes to floppy disk One floppy drive, named drive A If two floppy drives, second designated as drive B Also called secondary storage Floppy disk drive built into a desktop computer External floppy disk drive attaches to a computer with a cable p Fig. 7-6 Next

11 WHAT IS STORAGE? Floppy Disks Portable, inexpensive storage medium consisting of a thin, circular, flexible film enclosed in a squareshaped plastic shell Several sizes 8-inch 5.25-inch 3.5-inch shutter shell liner magnetic coating metal hub flexible thin film p Fig. 7-5

12 Floppy Disks How does a floppy disk drive work? Step 6. Read/write heads read data from and write data on floppy disk. Step 1. When you insert the floppy disk into drive, shutter moves to the side to expose the recording surface on disk. Step 2. When you initiate a disk access, circuit board on drive that contains electronics sends signals to control movement of read/write heads until they barely touch surface (film) inside floppy disk s shell. Step 5. Motor positions read/write heads over correct location on recording surface of disk. Step 4. Motor spins a shaft, which causes surface inside floppy Step 3. For write instructions, circuit board verifies whether or not disk can be written on. p Fig. 7-7 disk s shell to spin. Next Floppy Disks What are tracks and sectors? Track is narrow recording band that forms full circle on disk Sector stores up to 512 bytes of data Click to view Web Link, then click Floppy Disks below Chapter 7 Formatting prepares disk for use and marks bad sectors as unusable p Fig. 7-8 Next

13 Floppy Disks How do you compute a disk s storage capacity? Multiply number of sides, number of tracks, number of sectors per track, and number of bytes per sector For high-density disk: 2 sides 80 tracks 18 sectors per track 512 bytes per sector = 1,474,560 bytes Characteristics of a 3.5-inch High-Density Floppy Disk Capacity: 1.44 MB Sides: 2 Tracks: 80 Sectors per track: 18 Sectors per disk: 2880 p Next WHAT IS STORAGE? Characteristics of a Floppy Disk Uses magnetic patterns to store data Formatting Track Sector Write-protection Guidelines for floppy disk care Floppy disk drive

14 Floppy Disks What is a write-protect notch? Small opening with a cover that you slide Protects floppy disk from being erased accidentally notch open means you cannot write on the disk write-protected not write-protected notch closed means you can write on the disk hole on this side means disk is high density p Fig Next Zip Disks What is a Zip disk? Magnetic medium that stores 100 MB or 250 MB of data or 750 MB Used to back up and to transfer files Backup is duplicate of file, program, or disk in case original is lost c Zip disks require a Zip drivec chigh capacity drive that reads from and writes on a Zip disk REV disks (35GB) are similar. Zip disk External Zip drive p Fig Next

15 WHAT IS STORAGE? High-Capacity Removable Disks Capacities greater than 100 MB Many uses Graphics, audio, or video Transporting files Backups Zip drive WHAT IS STORAGE? Hard Disks Provide large storage capacity and high speed data access Sizes range from 30 GB to 100 GB Consists of several inflexible, circular disks, called platters Magnetic storage device Formatting

16 Hard Disks How does a hard disk work? Step 2. Small motor spins platters while computer is running. Step 1. Circuit board controls movement of head actuator and a small motor. Step 3. When software requests a disk access, read/write heads determine current or new location of data. Step 4. Head actuator positions read/write head arms over correct location on platters to read or write data. p Fig Next Hard Disks What is a cylinder? Vertical section of track through all platters Single movement of read/write head arms accesses all platters in cylinder platter track sector read/write head platter sides cylinder p Fig Next

17 Hard Disk Partitions and Logical Drives When installing an operating system on a new computer or after recovering from a hard disk failure, prepare the hard disk for use by: Partitioning the hard disk Creating logical drives Formatting logical drives A maximum of 4 primary partitions can be placed on a hard disk, but only 1 extended partition The way the Master Boot Record is structured determines this limitation. Disk Partitioning Partition disks to divide total storage space Primary partition the system s boot drive, used for system startup Extended partition the remaining drive space after you create the primary partition

18 Logical Disk Drives A disk partition must be assigned a logical drive identifier A primary partition is treated as a single logical drive An extended partition can be divided into multiple logical drives (drives D and E in figure) Logical Drive Format Low-level format: Prepares the hard disk before disk partitions can be defined Primarily the responsibility of the hard disk manufacturer High-level format: Logical drive formatting that prepares the drive for use by the operating system Creates the file system root directory and the files used to track disk space use

19 Hard Disks What are characteristics of a hard disk? Sample Hard Disk Characteristics Advertised capacity 40 GB Platters 2 Read/write heads 4 Cylinders 16,383 Bytes per sector 512 Sectors per track 63 Sectors per drive 78,165,360 Revolutions per minute 7,200 Transfer rate 100 MB per second Access time 9 ms actual disk capacity p Fig Next Head Crash on a Hard Disk What is a head crash? Occurs when read/write head touches platter surface Spinning creates cushion of air that floats read/write head above platter Clearance between head and platter is approximately two-millionths of an A inch smoke particle, dust particle, or human hair could render drive unusable read/write head hair clearance dust smoke platter p Fig Next

20 What is a disk cache? Portion of memory that processor uses to store frequently accessed items first request for data to disk cache in RAM Hard Disk Cache processor disk cache second request for data to HARD disk hard disk p Fig Next Magnetic Disk Controllers What is a disk controller? Chip and circuits that control transfer of items from disk SATA (Serial Advanced Technology Attachment) controller uses serial signals to transfer data, instructions, and information EIDE (Enhanced Integrated Drive Electronics) controller supports four hard disks, provides connections for CD and DVD drives SCSI (Small Computer System Interface) controller supports up to fifteen devices including hard disks, CD and DVD drives, tape drives, printers, scanners, network cards p. 364 Next

21 External Hard Disks What is an external hard disk? External hard disk freestanding hard disk that connects to system unit with a USB 2.0 cable Used to back up or transfer files Connects to USB 2.0 or Firewire port Maxtor One-Touch Backup: 250GB, Cost: < $ p Fig Next Removable Magnetic Disks What are external hard disks and removable hard disks? Used to back up or transfer files External hard disk freestanding hard disk that connects to system unit Removable hard disk hard disk that you insert and remove from hard disk drive Click to view Web Link, click Chapter 7, Click Web Link from left navigation, then click Hard Disks below Chapter 7 p. 364 Fig Next

22 WHAT IS STORAGE? CDs and DVDs Optical storage media Used to distribute software Laser reads pits on the surface Used on multimedia computers Several types CD-ROM DVD-ROM CDs and DVDs How does a laser read data on a CD or DVD? disc label lens Step 1. Laser diode shines a light beam toward disc. prism laser diode pit lightsensing diode land laser diode lens 0 Step 2. If light strikes 1 a pit, it scatters. If light strikes a prism land, it is reflected back toward diode. lightsensing diode Step 3. Reflected light is deflected to a light-sensing diode, which sends digital signals of 1 to computer. Absence of reflected light is read as digital signal of 0. p Fig Next

23 CDs and DVDs How is data stored on a CD or Typically stored in DVD? single track Track divided into evenly sized sectors that store items Single track spirals to edge of disc The track on a DVD is 7.5 miles long! disc sectors p Fig Next

24 WHAT IS STORAGE? Care of CDs and DVDs Can last from 5 to 100 years if properly cared for Never bend a disc Avoid extreme temperatures and humidity Keep away from contaminants Do not stack or touch discs Use a protective case WHAT IS STORAGE? CD-ROM Compact disc readonly memory Can contain text, graphics, video, as well as sound Can hold 650 MB of data Used for today s complex software

25 WHAT IS STORAGE? CD-R and CD-RW Compact disc-recordable Can write on each part of the disc only one time Cannot be erased Compact disc-rewriteable Can write on multiple times Erasable disc WHAT IS STORAGE? DVD-ROM and DVD+RW Digital video disc read-only memory (DVD- ROM) Can store from 4.7 GB to 17 GB High quality DVD-ROM drives May replace CDs, VCRs, and VHS tapes Digital video disc+rewritable (DVD+RW) Can write on multiple times Erasable disc

26 WHAT IS STORAGE? Miniature Mobile Storage Media WHAT IS STORAGE External and Removable Hard Disks External Hard Disk Separate hard disk that connects to a USB or FireWire port by cable USB Drives

27 File System Types Primary partitions and logical drives must be formatted so the operating system can use them Formatting creates the file system by adding information about how files should be stored on the drive to organize and manage disk storage File system types include: FAT 16, FAT32 and NTFS (Windows XP) Ext3 and ReiserFS (Linux) created by Hans Reiser Note: Hans Reiser was on trial in Feb 2008 for murdering File and Directory Permissions NTFS allows you to set permission bits on system resources In NTFS, you can protect files so that only certain users or groups of users can read them Concerns: If permissions are applied improperly, users may take security for granted Improperly set permissions can disrupt an operating system

28 Disk Convert Utility Information about the files on an NTFS volume and their attributes is stored in the MFT Convert utility used to convert a partition or logical drive from FAT or FAT32 to NTFS Disk Convert Utility Information about the files on an NTFS volume and their attributes is stored in the MFT Convert utility used to convert a partition or logical drive from FAT or FAT32 to NTFS [/v] convert drive /FS:NTFS convert C: /FS:NTFS

29 Disk Defragmenter Utility As files are created and deleted, a partition can become severely fragmented Fragmented files are no longer located in contiguous clusters You can use the Disk Defragmenter utility to defragment hard disks and put files back together in a contiguous format Disk Defragmenter What is a Disk Defragmenter? Reorganizes files and unused space into contiguous sectors on hard disk so programs run faster. fragmented disk file before defragmenting file after defragmenting p Fig Next

30 Chkdsk Utility You can use the Chkdsk utility in Windows NT/2000/XP to: Create and display a status report for a disk based on its file system List and correct errors on the disk Display the status of the disk in the current drive Click Start, click Run, type: chkdsk /F, Click OK Disk Cleanup Use the Disk Cleanup utility to recover the disk space used by: Temporary files Unused applications Files in the Recycle Bin Files you downloaded as part of Web pages Files created when Chkdsk attempted to recover lost file fragments (e.g. FILE0001.CHK)

31 CDs and DVDs What are CDs and DVDs? Flat, round, portable metal discs with protective plastic coating Can be read only or read/write Most PCs include CD or DVD drive, most play audio CDs Push the button to slide out the tray. Insert the disc, label side up. Push the same button to close the tray. p Fig Next Magnetic Tape How is data stored on a tape? Sequential access Reads and writes data consecutively, like music tape Unlike direct access used on floppy disks, Zip disks, hard disks, CDs, and DVDs which can locate particular item immediately Popular Types of Tape Name Abbreviation Storage Capacity Digital audio tape DAT 2 GB to 240 GB Digital linear tape DLT 20 GB to 220 GB Linear tape-open LTO 100 GB to 200 GB Quarter-inch cartridge QIC 40 MB to 25 GB Travan TR 8 GB to 40 GB p Fig Next

32 PC Cards What is a PC Card? (thickness is main difference) Adds capabilities to computer Credit-card-sized device commonly used in notebook computers PC Cards Category Thickness Use Type I 3.3 mm RAM, SRAM, flash memory Type II 5.0 mm Modem, LAN, SCSI, sound, TV turner, hard disk, or other storage Type III 10.5 mm Rotating storage such as a hard disk p Figs Next Home-Task: Go through Chapter 7 of Discovering Computers