Download - 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.
• 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.
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Storage Systems
• Hard Drives– 2 Types: SCSI and IDE
• IDE 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 USB
– Low-level formatted at the factory
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Low Level Formatting
• Low 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.
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Installing IDE/EIDE drives
• IDE supports TWO drives in a system – one master (boot disk) and one slave– set master and slave using jumpers
• EIDE supports FOUR drives per system– 2 drives on each of 2 cables– only one master, all others are slaves
• IDE and EIDE drives both use 40-pin ribbon cable aligned to pin 1
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Hard Drive
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Floppies
• Two sizes– 3.5 inch
– 5.25 inch
• 3.5 inch holds 1.44 MB for High density and 750 KB for Double Density
• Connected with 34 pin ribbon cable
• Two Floppy Drives possible
• Has twist in cable to distinguish A drive from B drive
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SCSI• Pronounced Scuzzy• Small Computer Systems Interface• For wide range of peripheral devices, including hard
disks, tape drives, optical drives, CD-ROMs and disk arrays.
• 8 devices can connect to a daisy chain• This chain must be terminated at both ends• Each device on chain is assigned unique device ID
number that is determined by jumpers or DIP switches
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Installing and configuring SCSI
• SCSI bus supports 8 devices
• There are eight SCSI IDs numbered 0 through 7
• ID 7 is always reserved for the SCSI host adapter
• SCSI hard disk, if used as a boot drive, is assigned SCSI ID 0
• If you have both IDE and SCSI hard drive, IDE drive should be boot drive
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Types of SCSIs
• SCSI 1- 5 MB transfer rate, Centronics 50 pin or DB 25, has 8 bit bus
• SCSI 2 -also SCSI Fast Wide, includes 16 bit bus , called Wide SCSI, and twice as fast transfer rate
• SCSI 3- Includes Ultra SCSI, Wide Ultra SCSI, and Ultra 2 SCSI, 16 bit bus with up to 80 MBps transfer rate
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RAID
• Redundant Array of Independent Disks
• Category 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
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RAID continued
• RAID 0- Striped disk without parity
• RAID 3- Parallel transfer with parity
• RAID 5- Data striping with parity
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How Data is Organized on Disk
• Tracks- – circular areas of the disk– Length of a track one circumference of disk– Over 1000 on a hard disk– Data first written to outer most track
• Sectors- – Divides tracks sections – On a floppy 9 sectors exits
• Cylinders- – Logical groupings of the the same track on each disk surface in a disk
unit• Clusters-
– Groups of sectors used by operating system– 64 sectors in one cluster
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Track=concentric
circle
Sector =small arc of track
Can store 512 bytes
Tracks and sectors
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Interleaving
• Allows the read/write head to use the rotation of the disk to its advantage
• One sector is written to and the disk skips to several sectors down
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Formatting
• Low level formatting done at factory– Builds the File Allocation Table (FAT)– Physically scans the disk media for defects
• Remember FAT is always located at Track 0
• High level formatting is automatically done during installation of operating system
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Operating System File Systems
• DOS uses FAT
• Windows 3.x uses Virtual FAT
• Win 95 uses VFAT and FAT32
• Win NT uses NTFS
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Partitioning
• FDISK command is used
• Divides 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
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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 GB• Following partition, the first sector on cylinder 0
reserved for master boot record
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Disk compression
• Reduce amount of space taken up by files by substituting codes for repeating patterns of data
• To access data on compressed disk, must load disk compression utility into RAM first
• This disk compression utility works between OS and disk controller to intercept requests and compress or decompress files- the result is slower disk access
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Backing up data
• Archival: full backup- contains everything from the hard disk
• Incremental: contains only files that have been modified since last (previous) backup
• Differential: backs up all the data modified since last full backup
• Copy backup: copy duplicate of file, directory, or disk to another disk
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CD ROM
• Capacity of 650 MB
• Transfer speeds of around 24X speed– X refers to the transfer speed in the first CD ROM,
which was 150 K
• CD is the slowest device on PC
• When installing to IDE system must be configured as slave
• WORM and EO