Transcript Presentation on File Managers

3 Computing System
Fundamentals
3.7 Utility Software
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3.7.1 File Managers
Utility software
• Software that performs general maintenance
behind the scenes.
• Often sooner or later gets incorporated into
the operating system (OS).
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File managers
• Part of the OS necessary to maintain the
computer’s file system in a logical and
efficient manner.
• They are responsible for...
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File managers
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copying files,
deleting files,
moving files between directories (folders),
renaming files,
formatting media such as hard disks and
floppy disks (see formatting later),
creating disk partitions...
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File managers
finding files by name, date, size, type, etc.,
sorting files by name, date, size, type, etc.,
creating directory structures,
printing files (i.e. copying files to printing
applications),
creating back-ups of the file system or
individual files (see section on Errors),
restoring files from back-ups.
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Formatting media
• All types of media need to be prepared in
some way for use on a computer system by
arranging the various sectors and tracks.
• Each OS will typically use a different media
format e.g. FAT32 on Windows.
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Data compression
• Used for two things:
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reducing the size of files and
combining several files into one file.
• Both are useful when transferring data across
(often slow) networks.
• Less relevant now we have
large hard drives(?).
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broadband and
Data compression
• Compression is used with media files such as
graphics (e.g. JPEG), music (e.g. MP3) and
video files (e.g. MP4).
• If some quality is lost in the compression
process it is called lossy compression, if not,
lossless.
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Data compression
• Short periods of silence in music files can be
represented by a number simply saying how
long they are.
• Areas of the same colour in graphics files by
a token for the colour and a definition of the
area it covers.
• Video compression formats e.g. MP4 only
save parts of the frame that changes e.g. a
speaker's mouth.
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Data compression
• An example of how text compression might
work:
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She sells seashells on the seashore.
• Certain combinations appear commonly (such
as "she") and can be represented by a single
token or symbol.
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Defragmentation
• This is used to rearrange the parts of files on
a file system so as to waste as little storage
as possible, speed up access to the files and
to move often used files to the front of the
disk.
• A file on a fresh disk will be stored in a
number of (initially consecutive) blocks.
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Defragmentation
• Here’s part of a hard disk drive:
• Suppose the yellow file gets deleted:
• A new file (larger than 4 blocks) can be stored
using its space, plus other sectors:
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Defragmentation
• Although the OS has split up (fragmented)
the green file, it can link its parts together
when the file is required.
• If this continues with the addition and deletion
of many files then a single large file can be
split up over different parts (even different
surfaces) of a disk and reading becomes less
efficient.
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Instantiating a student
• You can declare an array of students:
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Student [] register = new
Student [30];
• And place students in it:
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register [13] = new Student
(“Polly”,14,86);
• Or use them in for loops etc.
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