Coaxial cable

Coaxial cable:-With ``coax'', the medium consists of a copper core surrounded by insulating material and a braided outer conductor.Coaxial cable carries signals of higher frequency ranges than those in twisted-pair cable.
      Coax has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of the two.The outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit. This outer conductor is also enclosed in an insulating sheath, and the whole cable is
protected by a plastic cover.

Characteristics:-
*)Co-axial cable has superior frequency characteristics compared to twisted-pair and can be used for both analog and digital signaling.
*)Coaxial cables are used both for base band and broadband communication.
*)This cable offers bandwidths of 300 to 400 MHz facilitating high-speed data communication with low        bit-error rate.
*) In broadband signaling, signal propagates only in one direction, in contrast to propagation in both directions in base band signaling.

Applications:-
*)Coaxial cable was widely used in analog telephone networks where a single coaxial  network  could carry 10,000 voice signals.
*)the most popular use of co-axial cable is in cable TV (CATV) for the distribution of TV signals.
*)coaxial cable is used in traditional Ethernet LAN s.

                       

Data flow

Data flow--
The communication between two devices is:-
1)Simplex:-In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive .
Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output.
2.)Half-Duplex:-In half-duplex mode, each station can both transmit and receive, but not at the same time.:
When one device is sending, the other can only receive, and vice-versa.
The half-duplex mode is like a one-lane road with traffic allowed in both direct
ions. When cars are traveling in one direction, cars going the other way must wait.
3)Full-Duplex:-In full-duplex mode (duplex), both stations can transmit and receive simultaneously .
The full-duplex mode is like a two-way street with traffic flowing in both direct
ions at the same time. In full-duplex mode, signals going in one direction share the
capacity of the link with signals going in the other direction. This sharing can occur in
two ways: Either the link must contain two physically separate transmission paths, one
for sending and the other for receiving; or the capacity of the channel is divided.
between signals traveling in both directions.
One common example of full-duplex communication is the telephone network.

                              

Fiber-Optic Cable

Fiber-Optic Cable:-A fiber-optic cable is made of glass or plastic and transmits signals in the form of light.Light travels in a straight line as long as it is moving through a single uniform substance.
In fiber optic technology, the medium consists of a hair-width strand of silicon or glass, and the signal consists of pulses of light.It has a cylindrical shape and consists of three concentric sections: the core, the cladding, and the jacket.
   The core, innermost section consists of a single solid dielectric cylinder of diameter d1 and of refractive index n1. The core is surrounded by a solid dielectric cladding of refractive index n2 that is less than n1.The cladding is surrounded by a jacket made of plastic. The jacket is used to protect against moisture, abrasion, crushing and other environmental hazards.
   Optical fibers are available in two varieties; Multi-Mode Fiber (MMF) and Single-Mode Fiber (SMF).For multi-mode fiber the core and cladding diameter lies in the range 50-200µm and 125-400µm, respectively. Whereas in single-mode fiber, the core and cladding diameters lie in the range 8-12µm and 125µm, respectively.

Advantages:-
1.Higher bandwidth.:-Very high data rate, low error rate. 1000 Mbps (1 Gbps) over distances of kilometers common. Error rates are so low ,negligible.
2.)Less signal attenuation.
3.)Difficult to tap,  higher reliability of this medium.
4.light weight:-Much thinner (per logical phone line) than existing copper circuits.
5.Not susceptible to electrical interference (lightning) or corrosion (rust).
6.Greater repeater distance than coax.
7.)Resistance to corrosive materials. Glass is more resistant to corrosive materials than copper.
Disadvantages:-
*)installation and maintenance.
*)Difficult to tap. It really is point-to-point technology. In contrast, tapping into coax is trivial. No special training or expensive tools or parts are required.
*)One-way channel. Two fibers needed to get full duplex (both ways) communication.
*)Cost. The cable and the interfaces are relatively more expensive than those of other
guided media.

Functions of an Operating System Kernel

Functions of an Operating System Kernel-->
1.Process Management
•- Process creation and termination
• -Process scheduling and dispatching
•- Process switching
• -Process synchronization and support for interprocess communication
• -Management of process control blocks
2.Memory Management--
•- Allocation of address space to processes
• -Swapping
• -Page and segment management
3.I/O Management
•- Buffer management
•- Allocation of I/O channels and devices to processes
4.Support Functions--
• -Interrupt handling
-• Accounting
•- Monitoring

Process State

Process State:-For a program to be executed, a process, or task, is created for that program.As a process executes, it changes state. The state of a process is defined in part by the current activity of that process.dispatcher program that switches the processor from one process to another.

 Each process may be in one of the following states:-
*New: The process is being created.
*Running: Instructions are being executed.
*Waiting: The process is waiting for some event to occur (such as an I/O
completion or reception of a signal).
*Ready: The process is waiting to be assigned to a processor.
*Terminated: The process has finished execution.

MEMORY MANAGEMENT REQUIREMENTS

MEMORY MANAGEMENT REQUIREMENTS-->
                                    Relocation,Protection,Sharing,Logical organization,Physical organization.
1.Relocation--In a multiprogramming system, the available main memory is generally shared among a number of      processes.relocation is the process of swapping a process back in  memory .Once a program has been swapped out to disk,then we can put it into main memory at another area of memory.It is called relocation.so we need memory allocation for process to execute.and we need  MEMORY MANAGEMENT.
2.Protection--Each process should be protected against unwanted interference by other processes,
whether accidental or intentional. Thus, programs in other processes should not be able to reference memory locations in a process for reading or writing purposes without permission.
3.Sharing--Any protection mechanism must have the flexibility to allow several processes to
access the same portion of main memory.The memory management system must therefore allow controlled access to shared
areas of memory without compromising essential protection.
4.Logical Organization