OS

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O/S
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What does it do?
The O/S or operating system, allows the
applications on a PC to use its hardware. The
operating system or kernel is copied into the
computers RAM after the POST, this is known as
booting up. Here it remains for the entire
duration of which the the computer is switched on.
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IRQs
The o/s handles interrupt requests, these
allocate applications time to use the CPU.

• Multi user system
• Multitasking

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Backing Store Management
This area of the operating system manages the
disk drives.

• Puts data in RAM Quickly
• Maintains the disk index so files and free space
  can be found quickly

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Memory Management
Allocates the applications and itself memory. By
doing this it allows the user to more than one
program at once, and swap between them. Virtual
memory, page and swap files can also be used.
These uses the computers HDD as if it were RAM,
allowing the computer to run programs larger than
its RAM. Also known as mulit-programming.
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Manages Human Interface
The O/S manages its function according to the
users inputs on the mouse, keyboard or other
device. The culmination of which allows the
computer to perform useful functions.
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Pathnames
Folders or, directories, are organised in a tree
structure. The bottom of the tree being the
root.
The following diagram shows the directory
structure on a Windows computer system.
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The full name of the the selected file in the
diagram is as follows.
D\music\mp3s not on CD\American HiFi.mp3 Old
operating systems are restricted to the number of
allowed characters in a directory, for example
the same file under MS-DOS would be represented
as D\music\mp3sno1\Americ1.mp3
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Access Rights
Files can be given access rights, for example
read only files can be opened, but not modified.
More advanced systems can set permissions to
allow the file only to be executed and other such
functions. Passwords can be set for the access of
a specific file, or full control can be given.
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Example of a file with the read only attribute set
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Backing Up
There are five types of backup that most common
backup applications can perform Normal copies
all files to the medium and removes the backup
attribute. Incremental copes the files that
have been changed since previous
backup Differential copies files that have
changed, but doesnt remove the archive
attribute Copy - copies selected files, dont
remove attribute and doesnt affect normal
routine Daily - does files changes that day and
doesnt clear attribute