Secondary Storage: Hard Drives Chapter 8

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Secondary Storage Hard DrivesChapter 8

• David Turton
• Conestoga College
• Institute of Technology and Advanced Learning
• http//www.conestogac.on.ca/dturton
• Doon 1D17, x3610

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Components of a hard drive
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Drive Headscylinders, heads, sectors
track is redundant which platter? which
side?
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IDE Hard Drive

• Controller circuits are on the drive, hence
• Integrated Device Electronics (IDE)
• Enhanced IDE (EIDE)
• Redefinition of interface to motherboard
• Specs extended to provide common interface for
  other IDE devices
• 4 IDE devices per PC
• Faster transfer speeds
• 2 devices/cable
• Only 1 device on a cable can communicate at a
  time
• Not good for RAID5
• Both devices go at speed of slower device
• Serial ATA
• Revised IDE interface
• 1 device per cable
• Smaller footprint on motherboard
• Less waste space, better air flow in casing
• Potential of higher throughput than parallel

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IDE standards (ATA AT Attachment from IBM
"AT" PC)
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Serial vs Parallel Drives
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IDE Primary/Secondary- Master/Slave

• 2 IDE connectors or channels on motherboard
• Primary secondary channels
• Each channel can have 2 devices
• Master slave
• Set by jumpers on device
• O/S can only talk to 1 device on a channel at a
  time
• Must stop reading from one to write to the other
• Better CD-ROM on one channel, hard drive on other

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• Notes on "RAID" connectors
• They're RAID0
• no failure support
• Striped set
• Writes part of a record to one and another part
  to the other
• Very fast twice the read/write speed
• One drive fails, you lose everything

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Setting Jumperssingle, master, slave

• Master/slave
• Won't work if is only drive on cable
• Cable-select
• Small hole in cable
• Cuts a wire to one device
• Device nearest motherboard is master
• Only one that can use the cut wire.

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Other drive technologies

• SCSI Small Computer Standard Interface
• IDE drive fast bus controller
• 320MB/sec
• 3.2ms avg seek time
• 15 devices on bus
• Simultaneous device access
• Good for RAID
• Device-to-device transfer
• Fibre Channel
• Faster than SCSI with gt5 devices
• 126 devices on bus
• Used to connect servers to mass drive units
• fast xfer over a distance

• IEEE 1394 (FireWire)
• 63 devices on bus
• Serial 400 Mbits/sec
• External devices
• max 15 cable
• USB
• 127 devices on a bus
• USB 2.0 480Mbits/sec
• Sent in 1,500-byte packets
• 5V, 500mA per port
• Max cable 5M
• Max hubs in a line 5
• Therefore, max distance 30M

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Hard Drives Similarities to diskettes

• Has a file allocation table (FAT)
• Has a root directory
• Formatted into tracks and sectors
• each sector holds 512 bytes
• 2 read/write heads per platter
• Top and bottom

• Some differences
• multiple platters
• same track on each platter (top bottom) called
  a cylinder
• varying number of sectors per track
• fewer sectors as tracks get smaller
• OS cannot reference by sector and track
• OS only knows of sectors, if that

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IDE variable sectors/track
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Formatting a Hard Drive

• Track/sector marks no longer follow a simple
  pattern
• so these are written at the factory
• called a low level format
• FDISK
• partitions and makes logical drives
• Creates MBR
• Creates boots sectors
• On each logical drive

• OS does high-level format
• boot sector
• FAT
• root directory
• BIOS or generic low-level format
• Could destroy drive
• Use program from drive manufacturer

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Partitioning a Hard drive

• Drive is divided into 1 or more partitions
• Primary partition(s)
• 1 logical drive each
• Extended partition
• 1 or more logical drives
• Max 4 partitions
• Only 1 can be extended
• Partition table placed in MBR
• Head 0 track 0 sector 1

• Boot sector/record
• Placed on each logical drive
• Describe file system
• Can contain boot program
• Why partition?
• Separate data files from program files for backup
• Smaller clusters
• Each logical drive has own FAT, with finite
  entries per cluster
• More FAT entries, more clusters, fewer sectors
  per cluster
• Less waste space

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FDISK - partitioning a disk
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Installing a hard drive

• Decide
• which IDE channel
• sharing or not
• Set drive jumpers master/slave/only
• update system BIOS for large drives
• install in bay
• connect data cable to adapter port
• connect power cable
• partition format

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