FTP

File Transfer Protocol, it is an application protocol, part of the TCP/IP protocol stack, used for transmitting files between network nodes. FTP is defined in RFC 959.

WHAT IS SUBNET MASK ?

32-bit address mask used in IP to indicate the bits of an IP address that are being used for the subnet address.

What is Firewall ?

Firewall are hardware and software combinations that are built using routers, servers and variety of software. They sit at the most vulnerable point between a corporate network and the Internet and they can be as simple or complex as system administrators want to built them. Firewalls reduce the speed of access of networks.

Router or remote-access server (or several routers or access servers) designated as a buffer between connected networks. A firewall uses access lists and other methods to ensure the security that enforces a boundary between two or more networks.

A firewall can either be software-based or hardware-based and is used to help keep a network secure. Its primary objective is to control the incoming and outgoing network traffic by analyzing the data packets and determining whether it should be allowed through or not, based on a predetermined rule set. A network's firewall builds a bridge between an internal network that is assumed to be secure and trusted, and another network, usually an external (inter)network, such as the Internet, that is not assumed to be secure and trusted.

Many personal computer operating systems include software-based firewalls to protect against threats from the public Internet. Many routers that pass data between networks contain firewall components and, conversely, many firewalls can perform basic routing functions

Every time a corporation connects its internal computer network or LAN to the Internet, it faces potential danger regarding security. Due to the Internet's openness, every corporate network connected to it is vulnerable to attack. Crackers on the Internet could break into the corporate network and do harm in a number of ways. Some such methods are the  following:

a. They could copy or damage important data.
b. Damage individual computer data or the entire networking.
c. Use the corporate computer's resources or use the corporate network and resources as a way of posing to be a corporate employee.

The solution for all these problems and many more is to built 'firewalls' to protect its network. These firewalls allow anyone on the corporate network to access the Internet, but they stop crackers, hackers or others bent on to do mischief on the Internet from gaining access to the corporate network and causing damage.

Benefits of using a Firewall

i. Protection from services which are inherently more prone to attacks.
ii. Access to host in the network can be strictly controlled.
iii. Security is concentrated on a single firewall system. This leads to better implementation of authentication procedures.
iv. Logging and statistics of network use and misuse.
v. Policy enforcement.

Ethernet

LAN technology invented by Xerox Corporation and developed jointly by Xerox, Intel and Digital Equipment Corporation. Ethernet networks use CSMA/CD and run over a variety of cable types at 10 Mbps. Ethernet is similar to IEEE 802.3.

CSMA/CD

A contention method (carrier sense, multiple access, collision detect) in which a transmitting node first tests the channel and, if the channel is clear, then transmits the desired message. If two stations transmit at the same time, the collision is detected and retransmission is forced. Also Carrier Sense Multiple Access with Collision Detection. Media access mechanism wherein devices determine if another device is already transmitting before starting their own transmissions. If no transmission is sensed for a secific period of time, a device can transmit. If multiple devices transmit at once, a collision occurs and is detected by all colliding device. This collision subsequently delays retransmission from those devices for some random length of time. CSMA/CD is used by Ethernet and IEEE 802.3.

Transmission Modes

Transmission Modes

There are three modes of data transmission that corresponding to the three types of circuit available.

these modes are :-

1) Simplex :- In simplex communications mode, there is a one way communication transmission. Television transmission is a very good example of simplex communication. The main transmitter sends out a signal                    (broadcast ), but it does not expect a reply as the receiving units cannot issue a reply back to the transmitter.

it requires one wire only.

2) Half-duplex :- In half-duplex mode, both units communicate over the same medium, but only one unit can send at a time. While one is in send mode, the other unit is in receive mode. It is like two polite people talking to each other -- one talks, the other listens, but both of them could not talk at the same time.

It requires two wires. This is the most common type of transmission for voice communications.

The transmission of data to and from a hard disk is also done in half duplex mode.

3) Full-duplex or Duplex :- A full-duplex system is used that allows information to flow simultaneously in both directions on the transmission path. Use of a full-duplex line improves efficiency as the line turn-around time required in a half-duplex arrangement in eliminated.

It also requires four wires for full-duplex system.

Network Topology

The structure of interconnecting of nodes of a computer network.
Logical arrangement of network nodes and media within a networking structure.

Kernel And Shell

Kernel And Shell

Both the Shell and the Kernel are the Parts of this Operating System. These Both Parts are used for performing any Operation on the System. When a user gives his Command for Performing Any Operation, then the Request Will goes to the Shell Parts, The Shell Parts is also called as the Interpreter which translate the Human Program into the Machine Language and then the Request will be transferred to the Kernel. So that Shell is just called as the interpreter of the Commands which Converts the Request of the User into the Machine Language.

Kernel is also called as the heart of the Operating System and the Every Operation is performed by using the Kernel , When the Kernel Receives the Request from the Shell then this will Process the Request and Display the Results on the Screen.
The various Types of Operations those are Performed by the Kernel are as followings:-



1) It Controls the State the Process Means it checks whether the Process is running or Process is Waiting for the Request of the user.



2) Provides the Memory for the Processes those are Running on the System Means Kernel Runs the Allocation and De-allocation Process , First When we Request for the service then the Kernel will Provides the Memory to the Process and after that he also Release the Memory which is Given to a Process.



3) The Kernel also Maintains a Time table for all the Processes those are Running Means the Kernel also Prepare the Schedule Time means this will Provide the Time to various Process of the CPU and the Kernel also Puts the Waiting and Suspended Jobs into the different Memory Area.



4) When a Kernel determines that the Logical Memory doesn’t fit to Store the Programs. Then he uses the Concept of the Physical Memory which Will Stores the Programs into Temporary Manner. Means the Physical Memory of the System can be used as Temporary Memory.



5) Kernel also maintains all the files those are Stored into the Computer System and the Kernel Also Stores all the Files into the System as no one can read or Write the Files without any Permissions. So that the Kernel System also Provides us the Facility to use the Passwords and also all the Files are Stored into the Particular Manner.



As we have learned there are Many Programs or Functions those are Performed by the Kernel But the Functions those are Performed by the Kernel will never be Shown to the user. And the Functions of the Kernel are Transparent to the user.

Booting

Booting

When we start our Computer then there is an operation which is performed automatically by the Computer which is also called as Booting. In the Booting, System will check all the hardware’s and Software’s those are installed or Attached with the System and this will also load all the Files those are needed for running a system.


 In the Booting Process all the Files those are Stored into the ROM Chip will also be Loaded for Running the System. In the Booting Process the System will read all the information from the Files those are Stored into the ROM Chip and the ROM chip will read all the instructions those are Stored into these Files. After the Booting of the System this will automatically display all the information on the System. The Instructions those are necessary to Start the System will be read at the Time of Booting.



There are two Types of Booting 



1) Warm Booting: when the System Starts from the Starting or from initial State Means when we Starts our System this is called as warm Booting. In the Warm Booting the System will be Started from its beginning State means first of all, the user will press the Power Button , then this will read all the instructions from the ROM and the Operating System will b Automatically gets loaded into the System.



2) Cold Booting : The Cold Booting is that in which System Automatically Starts when we are Running the System, For Example due to Light Fluctuation the system will Automatically Restarts So that in this Chances Damaging of system are More. and the System will no be start from its initial State So May Some Files will b Damaged because they are not Properly Stored into the System.

What is Cache Memory?

It is a special buffer storage, smaller and faster than main storage, that is used to hold a copy of instructions and data that are likely to be needed next by the processor, and that have been obtained automatically from main storage.

Registers

Registers

Register are used to quickly accept, store, and transfer data and instructions that are being used immediately by the CPU, there are various types of Registers those are used for various purpose. Among of the some Mostly used Registers named as AC or Accumulator, Data Register or DR, the AR or Address Register, program counter (PC), Memory Data Register (MDR) ,Index register,Memory Buffer Register.

These Registers are used for performing the various Operations. While we are working on the System then these Registers are used by the CPU for Performing the Operations. When We Gives Some Input to the System then the Input will be Stored into the Registers and When the System will gives us the Results after Processing then the Result will also be from the Registers. So that they are used by the CPU for Processing the Data which is given by the User.

 Registers Perform:-

1)    Fetch: The Fetch Operation is used for taking the instructions those are given by the user and the Instructions those are stored into the Main Memory will be fetch by using Registers.

2)    Decode: The Decode Operation is used for interpreting the Instructions means the Instructions are decoded means the CPU will find out which Operation is to be performed on the Instructions.

3)    Execute: The Execute Operation is performed by the CPU. And Results those are produced by the CPU are then Stored into the Memory and after that they are displayed on the user Screen.

Types of Registers are as Followings

MAR stand for Memory Address Register

This register holds the memory addresses of data and instructions. This register is used to access data and instructions from memory during the execution phase of an instruction. Suppose CPU wants to store some data in the memory or to read the data from the memory. It places the address of the-required memory location in the MAR.

Program Counter 

The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 microprocessors, and sometimes called the instruction address register, or just part of the instruction sequencer in some computers, is a processor register

It is a 16 bit special function register in the 8085 microprocessor. It keeps track of the the next memory address of the instruction that is to be executed once the execution of the current instruction is completed. In other words, it holds the address of the memory location of the next instruction when the current instruction is executed by the microprocessor.

Accumulator Register

This Register is used for storing the Results those are produced by the System. When the CPU will generate Some Results after the Processing then all the Results will be Stored into the AC Register.

Memory Data Register (MDR)

MDR is the register of a computer's control unit that contains the data to be stored in the computer storage (e.g. RAM), or the data after a fetch from the computer storage. It acts like a buffer and holds anything that is copied from the memory ready for the processor to use it. MDR hold the information before it goes to the decoder.

MDR which contains the data to be written into or readout of the addressed location. For example, to retrieve the contents of cell 123, we would load the value 123 (in binary, of course) into the MAR and perform a fetch operation. When the operation is done, a copy of the contents of cell 123 would be in the MDR. To store the value 98 into cell 4, we load a 4 into the MAR and a 98 into the MDR and perform a store. When the operation is completed the contents of cell 4 will have been set to 98, by discarding whatever was there previously.

The MDR is a two-way register. When data is fetched from memory and placed into the MDR, it is written to in one direction. When there is a write instruction, the data to be written is placed into the MDR from another CPU register, which then puts the data into memory.

The Memory Data Register is half of a minimal interface between a micro program and computer storage, the other half is a memory address register.

Index Register

A hardware element which holds a number that can be added to (or, in some cases, subtracted from) the address portion of a computer instruction to form an effective address. Also known as base register. An index register in a computer's CPU is a processor register used for modifying operand addresses during the run of a program.

Memory Buffer Register

MBR stand for Memory Buffer Register. This register holds the contents of data or instruction read from, or written in memory. It means that this register is used to store data/instruction coming from the memory or going to the memory.

Data Register

A register used in microcomputers to temporarily store data being transmitted to or from a peripheral device.

What is CPU?

That portion of a computer that fetch's and executes instructions. It consists of an Arithmetic and Logic Unit (ALU), a Control Unit (CU) and registers. Often simply referred to as processor.

OSI MODEL

OSI stands for Open System Interconnection reference model. Network architectural model that consists of sevel layers, each of which specifies particular network functions such as addressing, flow control, error control encapsulation, and reliable message transfer. The OSI reference model is used unversally as a method for teaching and understanding network functionality.

What is FDDI (Fiber Distributed Data Interface)

A high speed protocol standard for sending network data over fiber cabling. An FDDI network using multimode fiber-optic cable can include as many as five hundred stations up to 2 kilometers. With single mode fiber, run length increases up to 60 kilometers. LAN standard specifying a 100-Mbps token passing network using fiber optic cable and a dual ring architecture to provide redundancy.