LIS508 lecture 5: storage devices

Thomas Krichel 2002-10-21

Today we have fun with

• Disks • Files, directories and links

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.

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.

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.

Formatting a floppy

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

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

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

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

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 “\”.

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

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.

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

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.

Sort items

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

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.

Finding a file

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

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.

• video

Next week

http://openlib.org/home/krichel

Thank you for your attention!