LIS508 lecture 5: storage devices

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LIS508 lecture 5 storage devices

• Thomas Krichel
• 2002-10-21

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Today we have fun with

• Disks
• Files, directories and links

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Files, directories and links

• Files are continuous chunks data on disks that
  are required for software applications.
• Directories are files that contain other files.
  Microsoft calls them folders.
• A link is a file that contain the address of
  another file. Microsoft call it a shortcut.

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Structure of a disk

• Disks are round devices divided into tracks and
  sectors.
• A hard disk may have several physical disks.
• Sector is 571 bytes long
• 512 bytes are used by the user
• The rest is reserved for disk operation
• The disk spins, a head reads and writes data.

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Data integrity

• The special data in each sector is kept there to
  try ensure that the user data is safe.
• It contains a summary of the user data.
• When the summary and the user data no longer
  match, the summary can be used to correct the
  user data.
• SMART disks are those that can monitor if they
  are a in good shape.

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Formatting a floppy

• Physical formatting
• writing tracks
• writing sectors
• Logical formatting
• labeling each sector
• create boot record
• create file allocation table (FAT)

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Formatting a hard disk

• That is the same as formatting a floppy but
• Between physical and logical formatting, the hard
  disk may be partitioned.
• This allows for several logical disks on the same
  physical disk
• Therefore the boot record is more complicated
  than on the floppy and called a master boot
  record MBR.
• Example dual boot Linux/Windows machine

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Windows logical disks

• Floppies use FAT12 format
• The boot records is exactly one sector long
• therefore called the boot sector
• Does not allow for long file names
• The logical disks on a hard disks may use FAT32
  format if larger than 512Mb
• System area
• Boot record
• FAT
• User area
• Can handle disks of the size of 2 tera bytes

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NTFS

• Is the file system for windows NT.
• In windows XP, Microsoft have limited FAT32 to a
  capability to handle disks up to 8 Gb, to
  encourage the use of NTFS.
• NTFS is a better file system
• FAT is in the middle
• Fragments less

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The root directory

• Like a directory in the ground floor of a
  Manhattan building.
• Root directory does not know where the file is
  stored, that is in the FAT.
• Root directory is called drive\ in windows,
  where drive is a letter identifying the drive. A
  drive is a physical device or a logical device
  found on a physical device.
• The directory separator in Windows is \.

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Unix file conventions

• In UNIX the root directory is /.
• / is the directory separator.
• A number of special files in /dev represent
  devices.
• Each device is mounted as a subdirectory of the
  root directory. Example
• mount /dev/fd0 /floppy

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Long and short file names

• DOS only had eleven byte file names, 8 for main
  name and three for the extension
• Names could be uppercase letters, numerals, and
  some other symbols.
• There is a generated short name that is used when
  windows writes to a disk that has a fat that does
  not support long names.
• All modern Windows versions use unicode for file
  names.

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Folders in Windows

• Rightclick, new allows you to create a new folder
  or shortcut
• Within a folder you can have different views of
  the files
• large icons (default)
• list, column
• Small icons, line)
• Details, shows date, type

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copy

• Either right-click and drag, select copy here
• Or use right-click cut, and then you can paste
  it.
• To delete, right-click and delete.
• And then go to the recycling box and delete it
  from there. Otherwise no free space is created.

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Sort items

• You can arrange icons by
• Name
• Type
• Size
• Date
• You can set auto arrange on (see tick mark)

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Windows explorer

• Shows directory tree and files in the current
  folder
• Width of both parts can be customized
• next to a folder suggests that it contains
  further folders
• Clicking on the plus can make the extra folders
  appear.

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Finding a file

• Find / files or folders
• Either name or substring
• Date range
• Type

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backups

• There is a song of the Beatles
• The backup utility is based in the system tools
  section of programs/accessories.
• It also has an emergency repair tool, that lets
  you fix things.
• It is best to define a backup job, and then run
  it at scheduled times.
• Time between jobs needs to be chosen with care.

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Next week

• video

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http//openlib.org/home/krichel

• Thank you for your attention!