Hard Disks

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Hard Disks. Low-level format - organizes both sides of each platter into tracks and sectors to define where items will be stored on the disk. Partitioning : divide hard disk into separate areas called partitions; each partition functions as if it were a separate hard disk drive. - PowerPoint PPT Presentation

Text of Hard Disks

  • Hard DisksLow-level format- organizes both sides of each platter into tracks and sectors to define where items will be stored on the disk. Partitioning: divide hard disk into separate areas called partitions; each partition functions as if it were a separate hard disk drive. High-level format defines the file allocation table (FAT) for each partition, which is a table of information used to locate files on the disk.

  • Storage SystemsHard Drives2 Types: SCSI and IDEIDE drives- originally developed as alternative to more expensive SCSI drives. Modern versions called EIDE drives. Support up to 4 multigigabyte drives. If you want more devices, use SCSI or USBLow-level formatted at the factory

  • Low Level FormattingLow level format scans disk for defects and sets aside sectors with defects so they are not used for data.IDE drives should never be low level formatted by a user or technician. Only high level format necessary.

  • Installing IDE/EIDE drivesIDE supports TWO drives in a system one master (boot disk) and one slaveset master and slave using jumpersEIDE supports FOUR drives per system2 drives on each of 2 cablesonly one master, all others are slavesIDE and EIDE drives both use 40-pin ribbon cable aligned to pin 1

  • Hard Drive

  • FloppiesTwo sizes3.5 inch5.25 inch3.5 inch holds 1.44 MB for High density and 750 KB for Double DensityConnected with 34 pin ribbon cableTwo Floppy Drives possibleHas twist in cable to distinguish A drive from B drive

  • SCSIPronounced ScuzzySmall Computer Systems InterfaceFor wide range of peripheral devices, including hard disks, tape drives, optical drives, CD-ROMs and disk arrays. 8 devices can connect to a daisy chainThis chain must be terminated at both endsEach device on chain is assigned unique device ID number that is determined by jumpers or DIP switches

  • Installing and configuring SCSISCSI bus supports 8 devicesThere are eight SCSI IDs numbered 0 through 7ID 7 is always reserved for the SCSI host adapterSCSI hard disk, if used as a boot drive, is assigned SCSI ID 0If you have both IDE and SCSI hard drive, IDE drive should be boot drive

  • Types of SCSIsSCSI 1- 5 MB transfer rate, Centronics 50 pin or DB 25, has 8 bit busSCSI 2 -also SCSI Fast Wide, includes 16 bit bus , called Wide SCSI, and twice as fast transfer rateSCSI 3- Includes Ultra SCSI, Wide Ultra SCSI, and Ultra 2 SCSI, 16 bit bus with up to 80 MBps transfer rate

  • RAIDRedundant Array of Independent DisksCategory of disk drives that employs 2 or more drives in combination for fault tolerance (error recovery)10 levels of RAID 3 on test will be:RAID 0, RAID 3, RAID 5

  • RAID continuedRAID 0- Striped disk without parityRAID 3- Parallel transfer with parityRAID 5- Data striping with parity

  • How Data is Organized on DiskTracks- circular areas of the diskLength of a track one circumference of diskOver 1000 on a hard diskData first written to outer most trackSectors- Divides tracks sections On a floppy 9 sectors exitsCylinders- Logical groupings of the the same track on each disk surface in a disk unitClusters- Groups of sectors used by operating system64 sectors in one cluster

  • Tracks and sectorsTrack=concentric circleSector =small arc of trackCan store 512 bytes

  • InterleavingAllows the read/write head to use the rotation of the disk to its advantageOne sector is written to and the disk skips to several sectors down

  • FormattingLow level formatting done at factoryBuilds the File Allocation Table (FAT)Physically scans the disk media for defectsRemember FAT is always located at Track 0High level formatting is automatically done during installation of operating system

  • Operating System File SystemsDOS uses FATWindows 3.x uses Virtual FATWin 95 uses VFAT and FAT32Win NT uses NTFS

  • PartitioningFDISK command is usedDivides hard drive into logical subdivisions which are seen by the operating system as separate logical hard disks. Hard drives divided into primary and extended partitions. The primary partition boots the system. Can have up to 4 primary partitions

  • Partitioning Extended can be divided up to 23 times on disk. Partitioning disks improves disk efficiency through reduced cluster size.In DOS, Win 3x and early versions of Win 95 a hard disk over 2 GB must be divided into smaller partions Now Win 95 and Win 98 can create a primary partition of up to 8 GBFollowing partition, the first sector on cylinder 0 reserved for master boot record

  • Disk compressionReduce amount of space taken up by files by substituting codes for repeating patterns of dataTo access data on compressed disk, must load disk compression utility into RAM firstThis disk compression utility works between OS and disk controller to intercept requests and compress or decompress files- the result is slower disk access

  • Backing up dataArchival: full backup- contains everything from the hard diskIncremental: contains only files that have been modified since last (previous) backupDifferential: backs up all the data modified since last full backupCopy backup: copy duplicate of file, directory, or disk to another disk

  • CD ROMCapacity of 650 MBTransfer speeds of around 24X speedX refers to the transfer speed in the first CD ROM, which was 150 KCD is the slowest device on PCWhen installing to IDE system must be configured as slaveWORM and EO


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