1 3 Computing System Fundamentals 3.7 Utility Software

3.7.1 File Managers

3 Utility software Software that performs general maintenance behind the scenes. Often sooner or later gets incorporated into the operating system (OS).

4 File managers Part of the OS necessary to maintain the computer’s file system in a logical and efficient manner. They are responsible for...

5 File managers ‣ 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...

6 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.

7 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.

8 Data compression Used for two things: ‣ 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 broadband and large hard drives(?).

9 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.

10 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.

11 Data compression An example of how text compression might work: ‣ She sells seashells on the seashore. Certain combinations appear commonly (such as "she") and can be represented by a single token or symbol.

12 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.

13 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:

14 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.

15 Instantiating a student You can declare an array of students: ‣ Student [] register = new Student [30]; And place students in it: ‣ register [13] = new Student (“Polly”,14,86); Or use them in for loops etc.