Operating System, and Network or Networking
In a computer network, two computers connected are able to communicate as long as communications are of both sides on the same network protocols. According to the OSI model, the various existing protocols are divided into seven levels, where a protocol for a given level can be combined with any protocol levels located above and below (see encapsulation).
An operating system typically contains several programs to exchange information in various protocols of levels 1-4. While levels 5-7 are supported by application software and middleware.
To exchange information according to protocols of Level 1 and 2, the operating system requests the operation of computer hardware through a pilot computer pilot who can be part of the system operation or be provided by the manufacturer of the equipment.
When sending information over the network, application software creates information, which is formatted according to the protocols of levels 7-5, then forward it to the operating system. Various programs of the operating system will cut the information into frames, then go to format and send frames according to the protocols of levels 4-1.
Upon receipt of frames from the network, different programs of the operating system will attempt to decode them according to various protocols at 1-4, and then convert the following frames in a continuous stream, which will be sent to the recipient software application. The software will then decode the stream according to the protocols of levels 5-7. The application software performs before a connection, that is to say, a logical link through which it will associate with a particular feed.
The exact choice of protocols depends on the affected computer and network links that will be used. Various configuration parameters can influence the choice of protocols. They allow for example to prevent the use of protocols allowed on the network concerned.
Access control logic
In a multi-operating system users a set of programs ensures the security of information stored in the memory and the availability of the computer, in order to preserve confidentiality and prevent manipulation performed by a user disrupt the computer use by other users. This feature is often absent from operating systems for personal devices.
In these operating systems any user must first identify himself or herself before using the computer. Then a program of the operating system checks the identity against a directory or a repository (see authentication).
The operating system then prepares a list of permitted and prohibited transactions with the user according to the regulations (also called policies) which have been introduced by the security administrator – the person responsible for information security.
During each operation requested by an application software, the operating system must first check if the user manipulates the software application is authorized to perform this operation. The verification is done on the basis of regulations and lists of access rights introduced by the security administrator. The operating system will refuse any unauthorized transaction and enter the refusal in an activity log.
In particular, the operating system may deny a user to read, modify, or delete a file, according to the list of access rights introduced for this file. The names of persons authorized to amend the lists of access rights is also indicated in the list of access rights.
The operating system will also disallow the decommissioning of core programs such as software programs or server operating system by any user who has not previously received the privilege to perform this operation – according to the rules introduced by the security administrator.
When a standalone software (computer bot) Operations requests to the operating system, software must first identify himself as a product and then, on the basis of this identity, the operating system performs the same checks as a individual.
The access control mechanisms have also effectively fight against malware – they often carry out operations that might disrupt the use of the computer.
A set of programs of the operating system receives the information submitted by application software, and places them on a digital image that will be sent to the hardware via a driver. In addition another set of programs receiving operations performed by the user through the pilot and transmit the relevant software. Both projects create man-machine interface that allows a user to interact with the machine.
The operating system can interact with a user through another computer or a terminal interface (distributed). The information sent by the application software will then be sent to another computer using a protocol designed for this purpose, while the other computer will send the operations performed by the user. See SSH, RFB or X Window System.
When the interface is text, the digital image is a grid that is placed in print, the grid typically comprises 80 columns and 35 lines. The interface can be manipulated with a keyboard. This type of interface, which has existed since the early days of computing [note 5] is now replaced by graphical interfaces.
The graphical user interface – GUI
In a GUI (Graphical User Interface or GUI), the digital image is composed by a program operating system by superposition of points, lines, symbols and letters. The interface is typically manipulated with a mouse on a WIMP (Windows, Icons, Menus and Pointing device). The digital image is created using the graphics processor on the computer.
When handling the mouse, the operating system moves the image element that is the pointer and performs the necessary calculations to determine which element of the image that lies just below. At each picture element may be associated with a program. A widget is a program that draws and animates an image whose appearance may be that of a push button, a lamp, a lift, a text box, menu, etc.. Various widgets are included with the operating system.
The graphical user interface programs are now (since 2009) included in all modern operating systems. The X Window System is the set of programs for graphical user interface included in all operating systems of the Unix family.
A software application used to assist the user in an activity. The software utilities are software applications that allow the user to perform basic manipulations such as start programs, copy files or change configuration settings. Various software tools are provided with operating systems.
A shell is a program that lets you run other programs by writing their name possibly followed by various parameters. It comes with several programs that allow file manipulation (copy, rename, etc.). This type of program is used to perform manipulations or run scripts – sequences of manipulations pre-recorded (see ordering information).
A desktop environment is a program in which the various elements of the computer (programs, files, and disks) are presented as icons on which you can perform different actions. It can run programs and perform various file operations (copying, renaming, moving or deleting, etc.)
Some programs serve the user to change the configuration settings of the operating system. They offer multiple choice lists and perform validity checks before changing settings.
Other programs used to install software, that is to say, copy the files in the locations provided for that purpose, and perform configuration changes needed to make the software operational. These programs can also be used to view the list of software currently installed in the computer.
An operating system multi-user is typically provided with programs to monitor the activity on the computer – consulting activity logs – or edit the lists of access rights to authorize or prohibit a file to some users.
An operating system is typically organized into distinct layers [T 12].
The top layer is the programming interface with application software (which includes software utilities included with the operating system).
In the center is one or more layers which contain the main components of the operating system such as programs for file systems and networking, memory management (see above), the pilots, the scheduler, the interrupt handler [T 13].
The lower layer, called HAL (Hardware Abstraction Layer English Short HAL), is responsible for hiding the physical characteristics [T 14].
Kernel operating system – The core
The core (kernel English) is a single memory space, which is placed in all or part of the operating system. In common parlance, the term kernel refers to the location, and all of its programs and form the heart of the rigid operating system. The content of the nucleus can not be inadvertently altered by software applications – a modification would crash the computer.
The architecture is said to be monolithic kernel where all the programs of the operating system (especially the drivers, programs that deal with the network file system) resides in kernel space. In this architecture each use of a function of the programming interface causes a context switch and the transition kernel mode (see above).
Linux, FreeBSD, OpenVMS and Solaris operating systems are monolithic stone.
The architecture is called micro-kernel (also called the microkernel) when the kernel contains the bare minimum, ie the scheduler and the program that simulates virtual memory, and the vast majority of programs are outside: drivers, programs that deal with file systems or graphical user interface and application software.
In this architecture, the many programs that are outside the core are isolated from each other, are implemented as application software – in competition – and use the kernel facility to exchange messages. The use of the functions of the programming interface involves the issuance of new messages.
Minix, BeOS, Mac OS X and QNX operating systems are micro-kernel.
Various operating systems have an architecture that has some characteristics of micro-kernels and monolithic kernels simultaneously. This architecture is called hybrid core macro-or micro-kernel modified kernel.
In this architecture, all the programs of the operating system reside in the nucleus, like a monolithic kernel. However many programs of the operating system are executed in competition as application software, like the micro-kernel architecture (kernel processes).
For the kernel process, the scheduler performs context switches between processes in the same manner as between application software, these processes use the functions of the scheduler to exchange messages and use functions API results in the emission of messages. Windows NT or NetWare operating systems are core hybrid.
In the exo-kernel architecture (Greek exos = off), there is no single location, and the operating system is composed of programs and software libraries of the same construction as those of application software.
Using a functional programming interface causes the execution of instructions in a software library of the operating system without requiring a context switch. A software library is used for transmitting and receiving messages between processes, the scheduler instructions are included in this library.
Mac OS, AmigaOS and Oberon are operating systems architecture exo-kernel.