I/O devices are very important in the computer systems.They provide users the means of interacting with the system. So there is a separate I/O system devoted to handling the I/O devices.The different Components of the I/O systems are −I/O HardwareThere are many I/O devices handled by the operating system such as mouse, keyboard, disk drive etc. There are different device drivers that can be connected to the operating system to handle a specific device. The device controller is an interface between the device and the device driver.A diagram to represent this is −I/O Application InterfaceThe user applications can access all ... Read More

Protection and security requires that computer resources such as CPU, softwares, memory etc. are protected. This extends to the operating system as well as the data in the system. This can be done by ensuring integrity, confidentiality and availability in the operating system. The system must be protect against unauthorized access, viruses, worms etc. Threats to Protection and Security A threat is a program that is malicious in nature and leads to harmful effects for the system. Some of the common threats that occur in a system are − Virus Viruses are generally small snippets of code embedded in a ... Read More

A computer system uses many devices, arranged in different ways to solve many problems. This constitutes a computing environment where many computers are used to process and exchange information to handle multiple issues.The different types of Computing Environments are −Let us begin with Personal Computing Environment −Personal Computing EnvironmentIn the personal computing environment, there is a single computer system. All the system processes are available on the computer and executed there. The different devices that constitute a personal computing environment are laptops, mobiles, printers, computer systems, scanners etc.Time Sharing Computing EnvironmentThe time sharing computing environment allows multiple users to share ... Read More

The kernel data structures are very important as they store data about the current state of the system. For example, if a new process is created in the system, a kernel data structure is created that contains the details about the process.Most of the kernel data structures are only accessible by the kernel and its subsystems. They may contain data as well as pointers to other data structures.Kernel ComponentsThe kernel stores and organizes a lot of information. So it has data about which processes are running in the system, their memory requirements, files in use etc. To handle all this, ... Read More

A communication satellite is an artificial satellite that acts as a large repeater in the sky. It receives signals from the source transmitter, amplifies using transponders, and relays them to the receiver. Thus, it creates a communication channel between locations of the earth that would not have been able to communicate due to long distance or obstruction by earth’s curvature.Communication satellites may be owned by government or private organizations. Presently, there are more than 2000 communication satellites in the sky. Some of its uses are −InternetMilitary operationsTelevisionTelephoneRadioCommunication satellites are broadly categorized into three types depending upon the orbit in which ... Read More

Electromagnetic waves within the frequency range of 400 THz – 790 THz are detected by the human eye. Light transmission is line of sight propagation and is blocked by obstacles. Laser Signals Optical signalling can be obtained by laser signals. For example, the LANs in two buildings can be connected by installing laser signalling system on the rooftops. Laser rays are unidirectional. So both the transmitter and the receiver need perfectly aligned photo-emitter and photo-detector. Visual Light Communication A more used variant of light transmission is visual light communication (VLC). VLC refers to data communication using visible ... Read More

Infrared waves are those between the frequencies 300GHz and 400THz in the electromagnetic spectrum. Their wavelengths are shorter than microwaves but longer than visible light. Infrared propagation is line of sight. They cannot penetrate walls and sun’s infrared rays interfere with these rays. So cannot be used for long – range communication. As their usage is confined within closed space, they do not need any government permissions for their applications. Applications of Infrared Waves in Communications Remote controls for television, stereos and other home appliances. Wireless LANs Wireless modem, keyboard, mouse, printer etc Fire detectors Night vision ... Read More

In the electromagnetic spectrum, waves within the frequencies 1GHz to 300GHz are called microwaves.Features of MicrowavesMicrowaves travel in straight lines, and so the transmitter and receiver stations should be accurately aligned to each other.Microwave propagation is line – of – sight propagation. So, towers hoisting the stations should be placed so that the curvature of the earth or any other obstacle does not interfere with the communication.Since it is unidirectional, it allows multiple receivers in a row to receive the signals without interference.Microwaves do not pass through buildings. So, indoor receivers cannot be used effectively.Microwaves are often refracted by the ... Read More

In the electromagnetic spectrum, all omnidirectional waves in the frequencies 3KHz to 1GHz are called radio waves. They are widely used for communications since they are easy to generate, can travel long distances and can penetrate buildings. Radio waves have omnidirectional antennas, i.e. antennas that can send signals in all directions. The properties of radios waves vary according to their frequencies. However, radio waves at all frequencies are prone to interference from electrical equipments like motors etc. Low and Medium Frequency Radio Waves Low and medium frequency radio waves can pass through obstacles and have ground propagation. However, the ... Read More

The electromagnetic spectrum is the entire range of electromagnetic radiation according to the wavelength or frequencies. It has a range of frequencies from 1Hz to Hz. The waves in order of increasing frequencies are radio waves, microwaves, infrared rays, visible light, UV rays, X-rays and gamma rays.Among these range, the frequencies between Hz to Hz are used for communication. The following diagram shows the electromagnetic spectrum. The first figure gives the full range of frequency spectrum while the second figure elaborates that part of the spectrum which can be used for data communication − The ... Read More