Cmf Terms Final

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1. MAIN MEMORY (RAM)

If we were to sum all the bits of all registers within CPU, the total amount of memory probably

would not exceed 5,000 bits. Most computational tasks undertaken by a computer require a lotmore memory. Main memory is the next fastest memory within a computer and is much larger

in size. Typical main memory capacities for different kinds of computers are: PC 512MB,

fileserver 2GB, database server 8GB. Computer architectures also impose an architectural

constraint on the maximum allowable RAM. This constraint is normally equal to 2WordSize

memory locations.

RAM (Random Access Memory) is the most common form of Main Memory. RAM is normally

located on the motherboard and so is typically less than 12 inches from the CPU. ROM (ReadOnly Memory) is like RAM except that its contents cannot be overwritten and its contents are

not lost if power is turned off (ROM is non-volatile).

Although slower than register memory, the contents of any location in RAM can still be read

or written very quickly. The time to read or write is referred to as the access time and is

constant for all RAM locations.In contrast to register memory, RAM is used to hold both

program code (instructions) and data (numbers, strings etc). Programs are loaded into RAM

from a disk prior to execution by the CPU.

Locations in RAM are identified by an addressing scheme e.g. numbering the bytes in RAM

from 0 onwards. Like registers, the contents of RAM are lost if the power is turned off.

2. DMA (DIRECT MEMORY ACCESS)

Stands for "Direct Memory Access.DMA is a method of transferring data from the computer's

RAM to another part of the computer without processing it using the CPU. While most data that

is input or output from your computer is processed by the CPU, some data does not require

processing, or can be processed by another device. In these situations, DMA can save processing

time and is a more efficient way to move data from the computer's memory to other devices. For

example, a sound card may need to access data stored in the computer's RAM, but since it can

process the data itself, it may use DMA to bypass the CPU. Video cards that support DMA can


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also access the system memory and process graphics without needing the CPU. Ultra DMA hard

drives use DMA to transfer data faster than previous hard drives that required the data to first be

run through the CPU.

In order for devices to use direct memory access, they must be assigned to a DMA channel. Each

type of port on a computer has a set of DMA channels that can be assigned to each connected

device. For example, a PCI controller and a hard drive controller each have their own set of

DMA channels.

3. INTERRUPT

Interrupt refers to the transfer of program control from a currently running program to another

service program as a result of an external or internal generated request.

There are three types of interrupts which the CPU recognizes.

Hardware Interrupt- This is any type of hardware event such as a key pressed on the keyboard,

a hard disk completing the reading or writing of data, or the reception of an ethernet packet, etc.

Many operating systems program a clock to issue interrupts at regular intervals so that the kernel

is guaranteed to get control on a regular basis even if no hardware events occur and a user

program never releases the CPU.

Software Interrupt- When a user program needs to make a system call to the operating system,

such as for I/O or to request more memory, it may issue a special instruction called a software

interrupt to cause the CPU to switch processing to the kernel.

Trap- A trap is issued by the CPU itself when it detects that something is wrong or needs special

attention. In most cases a trap is issued when a user program performs an illegal instruction such

as a divide by zero error or illegal memory reference.

4. CACHE MEMORY

Cache memory is a high speed memory buffer that temporarily stores data that processor needs.

It stores random data usually stores on the first in first out basis. It enables the processor to

continue working either at full speed. Cache memory is basically made up of static RAM


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integrated into the processor. In static RAM binary values are stored using flip flops and logic

gates. It holds its data until the power is supplied.

Cache memory is usually placed between the processor and the main memory. Basically the

main function of the cache memory is to accelerate your computer. Cache is a technology based

on the memory subsystem of your computer. Caching allows you to do your computer tasks

more rapidly. The value of cache is that it is much faster than the normal memory. The data is

searched on the basis of address.

There are two types of cache memory that is level 1 and level 2. Level 1 is memory that is of

very high speed and can be accessed easily with the zero wait state. If the required data or

instruction is not present on the level1 then level 2 is tried next. Today level 1 cache memory is

mostly implemented within the processor, with level 2 referring to cache memory on

motherboard. Nowadays, level2 cache is also becoming available on processor.

5.STACK

In computer science, a stack is a last in, first out (LIFO) abstract data type and data structure. A

stack can have any abstract data type as an element, but is characterized by only three

fundamental operations:push,pop and stack top. The push operation adds a new item to the top

of the stack, or initializes the stack if it is empty. If the stack is full and does not contain enoughspace to accept the given item, the stack is then considered to be in an overflow state. The pop

operation removes an item from the top of the stack. A pop either reveals previously concealed

items, or results in an empty stack, but if the stack is empty then it goes into underflow state (It

means no items are present in stack to be removed). The stack top operation gets the data from

the top-most position and returns it to the user without deleting it. The same underflow state can

also occur in stack top operation if stack is empty.

A stack is a restricted data structure, because only a small number of operations are performed

on it. The nature of the pop and push operations also means that stack elements have a natural

order. Elements are removed from the stack in the reverse order to the order of their addition:

therefore, the lower elements are those that have been on the stack the longest.
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Representation of stack

6.LOGICGATES

A logic gate performs a logical operation on one or more logic inputs and produces a single logic

output. The logic normally performed is Boolean logic and is most commonly found in digital

circuits. Logic gates are primarily implemented electronically using diodes or transistors, but can

also be constructed using electromagnetic relays, fluidics, optics, molecules, or even mechanical

elements. A logic level is represented by a voltage or current, (which depends on the type of

electronic logic in use). Each logic gate requires power so that it can source and sink currents to

achieve the correct output voltage. In logic circuit diagrams the power is not shown, but in a full

electronic schematic, power connections are required.

7.VIRTUALMEMORY

In computing, virtual memory is a memory management technique developed for multitasking

Kernals. This technique virtualizes a computer architectures various forms of computer data

storage(such as random access memory and Disk storage), allowing a program to be designed as

though there is only one kind of memory, "virtual" memory, which behaves like directly

addressable read/write memory (RAM).

Systems that employ virtual memory:

Use hardware memory more efficiently than do systems without virtual memory.

Make the programming of applications easier:

By hiding fragmentation.

By delegating to the kernel the burden of managing the memory hierarchy.
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8. INSTRUCTION EXECUTION CYCLE

In order to execute an instruction program, the control unit has to issue and coordinate a series of

micro-instructions. These micro-instructions form the fetch-execute cycle. The operation of theCPU is usually described in terms of the Fetch-Execute cycle.

Fetch-Execute Cycle The cycle raises many interesting questions, e.g.

Fetch theInstruction What is an Instruction? Where is the Instruction? Why does it

need to be fetched? Isn't it okay where it is? How does the

computer keep track of instructions? Where does it put the

instruction it has just fetched?

Increment the Program

Counter

What is the Program Counter? What does the Program Counter

count? Increment by how much? Where does the Program

Counter point to after it is incremented?

Decode the Instruction Why does the instruction need to be decoded? How does it get

decoded?

Fetch the Operands What are operands? What does it mean to fetch? Is this fetching

distinct from the fetching in Step 1 above? Where are the

operands? How many are there? Where do we put the operands

after we fetch them?

Perform the Operation Is this the main step? Couldn't the computer simply have done

this part? What part of the CPU performs this operation?

Store the results What results? Where from? Where to?

Repeat forever Repeat what? Repeat from where? Is it really an infinite loop?

Why? How do these steps execute any instructions at all?

9.COMPILER

A compiler is a computer program (or set of programs) that transforms source code written in a

programming language (the source language) into another computer language (the target


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language, often having a binary form known as object code.) The most common reason for

wanting to transform source code is to create an executable program.

The name "compiler" is primarily used for programs that translate source code from a high-level

programming language to a lower level language (e.g., assembly language or machine code). If

the compiled program can run on a computer whose CPU or operating system is different from

the one on which the compiler runs, the compiler is known as a cross-compiler.

A compiler is likely to perform many or all of the following operations: lexical analysis,

preprocessing, parsing, semantic analysis (Syntax-directed translation), code generation, and

code optimization.

10. OPERATING SYSTEM

An operating system (OS) is a set of programs that manage computer hardware resources and

provide common services for application software. The operating system is the most important

type ofsystem software in a computer system. A user cannot run an application program on the

computer without an operating system, unless the application program is self booting.

Time-sharing operating systems schedule tasks for efficient use of the system and may also

include accounting for cost allocation of processor time, mass storage, printing, and other

resources.For hardware functions such as input and output and memory allocation, the operating system

acts as an intermediary between application programs and the computer hardware, although the

application code is usually executed directly by the hardware and will frequently call the OS or

be interrupted by it. Operating systems are found on almost any device that contains a

computerfrom cellular phones and video game consoles to supercomputers and web servers.

The basic functions that an Operating System should provide include :

CPU and Process Management

Memory Management

I/O Management

Information And Storage Management

Network Management

User Interface
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Program Execution

Security

Device Management

Resource Allocation and Accounting

11. BIOS

BIO (basic input/output system) is the program a personal computer's microprocessor uses to

get the computer system started after you turn it on.

It also manages data flow between the computer's operating system and attached devices

such as the hard disk, video adapter, keyboard, mouse, and printer. BIOS is an integral part

of your computer and come with it when you bring it home. (In contrast, the operating

system can either be preinstalled by the manufacturer or vendor or installed by the user.)

BIOS is a program that is made accessible to the microprocessor on an erasable

programmable read-only memory (EPROM) chip. When computer is turned on, the

microprocessor passes control to the BIOS program, which is always located at the same

place on EPROM.

When BIOS boots up (starts up) your computer, it first determines whether all of the

attachments are in place and operational and then it loads the operating system (or key parts

of it) into your computer's random access memory (RAM) from your hard disk or diskette

drive. With BIOS, your operating system and its applications are freed from having to

understand exact details (such as hardware addresses) about the attached input/output

devices. When device details change, only the BIOS program needs to be changed.

Sometimes this change can be made during your system setup. In any case, neither your

operating system nor any applications you use need to be changed.

Although BIOS is theoretically always the intermediary between the microprocessor and I/O

device control information and data flow, in some cases, BIOS can arrange for data to flow

directly to memory from devices (such as video cards) that require faster data flow to be

effective.


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12. BYTE

A byte is a set of 8 bits that represent a single character in the computer's memory. Do not

confuse this term with "bite," as in taking a bite of a cookie, because that is totally different.

While bits are often used to measure data transfer speeds, bytes are used to measure file

sizes, hard disk space, and computer memory. Larger amounts of data are measured in units

such as megabytes, gigabytes, and terabytes.

For example, one kilobyte is equal to 1,024 bytes.In most computer systems, a byte is a unit

of data that is eight binary digits long.

A byte is the unit most computers use to represent a character such as a letter, number, or

typographic symbol (for example, "g", "5", or "?").

A byte can also hold a string of bits that need to be used in some larger unit for application

purposes (for example, the stream of bits that constitute a visual image for a program that

displays images or the string of bits that constitutes the machine code of a computer

program).

In some computer systems, four bytes constitute a word, a unit that a computer processor.

13. REGISTER MEMORY

Registers are memories located within the Central Processing Unit (CPU). They are few in

number (there are rarely more than 64 registers) and also small in size, typically a register is less

than 64 bits; 32-bit and more recently 64-bit are common in desktops.

The contents of a register can be read or written very quickly however, often an order of

magnitude faster than main memory and several orders of magnitude faster than disk memory.

Different kinds of register are found within the CPU. General Purpose Registers are available

for general use by the programmer. Unless the context implies otherwise well use the term

"register" to refer to a General Purpose Register within the CPU. Most modern CPUs have

between 16 and 64 general purpose registers. Special Purpose Registers have specific uses and

are either non-programmable and internal to the CPU or accessed with special instructions by the

programmer. Examples of such registers that we will encounter later in the course include: the


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Program Counter register (PC), the Instruction Register (IR), the ALU Input & Output registers,

the Condition Code (Status/Flags) register, the Stack Pointer register (SP). The size (the number

of bits in the register) of the these registers varies according to register type. The Word Size of

an architecture is often (but not always!) defined by the size of the general purpose registers.

In contrast to main memory and disk memory, registers are referenced directly by specific

instructions or by encoding a register number within a computer instruction. At the

programming (assembly) language level of the CPU, registers are normally specified with

special identifiers (e.g. R0, R1, R7, SP, PC)

As a final point, the contents of a register are lost if power to the CPU is turned off, so registers

are unsuitable for holding long-term information or information that is needed for retention after

a power-shutdown or failure. Registers are however, the fastest memories, and if exploited can

result in programs that execute very quickly.

14. RISC (REDUCED INSTRUCTION SET COMPUTER)

RISC is a class of computer architectures featuring a small number of primitive instructions, a

constant hardware instruction length (in bits), and no memory accesses except by load" and

store" instructions. The objective of a RISC architecture is to reduce the number of clock

periods per (integer) instruction to 1 for most executions, in order to maximizeperformance.

The following characteristics are typical of RISC architectures. Although none of these are

required for anarchitecture to be called RISC, this list does describe most current RISC

architectures, including the SPARC design.

Singlecycle execution: Most instructions are executed in a single machine cycle.

Hardwired control with little or no microcode: Microcode adds a level of complexity and

raises the number of cycles per instruction.

Load/Store, register-to-register design: All computational instructions involve registers.Memory accesses are made with only load and store instructions.

Simple fixed-format instructions with few addressing modes: All instructions are the

same length (typically 32 bits) and have just a few ways to address memory.

Pipelining: The instruction set design allows for the processing of several instructions at

the same time.


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Highperformance memory: RISC machines have at least 32 generalpurpose registers

and large cache memory.

Migration of functions to software: Only those features that measurably improve

performance are implemented in hardware. Software contains sequences of simple

instructions for executing complex functions rather than complex instructions

themselves, which improves system efficiency.

More concurrency is visible to software: For example, branches take effect after

execution of the following instruction, permitting a fetch of the next instruction during

execution of the current instruction.

The real keys to enhanced performance are single-cycle execution and keeping the cycle time as

short as possible. Many characteristics of RISC architectures, such as load/store and register-to-

register design, facilitate single-cycle execution. Simple fixed-format instructions on the other

hand, permit shorter cycles by reducing decoding time.

15. BOOTING

To boot a computer is to load an operating system into the computer's main memory or random

access memory (RAM). Once the operating system is loaded, it's ready for users to run

applications. Sometimes there is an instruction to "reboot" the operating system. This simply

means to reload the operating system. Booting or loading an operating system is different than

installing it, which is generally an initial one-time activity. When you install the operating

system, you may be asked to identify certain options or configuration choices. At the end of

installation, your operating system is on your hard disk ready to be booted (loaded) into random

access memory, the computer storage that is closer to the microprocessor and faster to work with

than the hard disk. Typically, when an operating system is installed, it is set up so that when youturn the computer on, the system is automatically booted as well. If you run out of storage

(memory) or the operating system or an application program encounters an error, you may get an

error message or your screen may "freeze". In these events, you may have to reboot the operating

system.


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16. CISC (COMPLEX INSTRUCTION SET COMPUTER)

A complex instruction set computer is a computer where single instructions can execute several

low-level operations (such as a load from memory, an arithmeticoperation, and a memory store)and/or are capable of multi-step operations or addressing modes within single instructions.

Examples of CISC instruction set architectures are System/360 through z/Architecture, PDP-11,

VAX, Motorola 68k, and x86.

CISC characteristics:

Memory accesses and address arithmetic are tightly bound to instructions

Rely on few registers, more memory references

Note that memory hasn't kept pace with processor clock rate

many instructions that access memory directly

large number of addressing modes

variable length instruction encoding

support for misaligned accesses

17. INTERLEAVED MEMORY

When memory consists of several memory modules, some address bits will select the module,

and the remaining bits will select a row within the selected module.

When the module selection bits are the least significant bits of the memory address we call

the resulting memory a low-orderinterleaved memory.

When the module selection bits are the most significant bits of the memory address we call

the resulting memory a high-order interleaved memory.

Interleaved memory can yield performance advantages if more than one memory module can be

read/written at a time:-

(I) for low-order interleave if we can read the same row in each module. This is good for a

single multi-word access of sequential data such as program instructions, or elements in a

vector,
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(ii) for high-order interleave, if different modules can be independently accessed by different

units. This is good if the CPU can access rows in one module, while at the same time, the

hard disk (or a second CPU) can access different rows in another module.

18. BYTE ORDERING

The ordering of bytes within a multi-byte data item defines the endian-ness of the architecture.

In BIG-ENDIAN systems the most significant byte of a multi-byte data item always has the

lowest address, while the least significant byte has the highest address.

In LITTLE-ENDIAN systems, the least significant byte of amulti-byte data item always has the

lowest address, while the most significant byte has the highest address.

In the following example, table cells represent bytes, and the cell numbers indicate the address of

that byte in main memory. Note: by convention we draw the bytes within a memory word left-to-

right for big-endian systems, and right-to-left for little-endian systems.

Word

Address

Big-Endian Word

Address

Little-Endian

0 0 1 2 3 0 3 2 1 0

4 4 5 6 7 4 7 6 5 4

8 8 9 10 11 8 11 10 9 8

12 12 13 14 15 12 15 14 13 12

MSB -> LSB MSB > LSB

19. INSTRUCTION

Instruction isthe binary code that causes a computer's hardware to perform a specific task. It is

also calleda hardware instruction.Instructionis a line of an assembly-language program that the


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assembler translates into a hardware instruction. In assembly language an instruction is coded in

a rigid format, such as

operation operand1,operand2,operand3

where the operands are registers, memory locations or numerical constants. An assembly-

language program consists of a sequence of directives, declarations and instructions. Instructions

are available in the Instruction set architecture of a computer system to the assembler

programmer. Computers that share the same instruction set architecture need not have the same

clock frequency, peripheral devices, or operating system.

Machine instructions are classified into the following three categories:

data transfer operations (memory, register, register, register)

arithmetic logic operations (add, sub, and, or, xor, shift, etc)

program control operations (branch, call, interrupt)

20. COMPUTER BUS

A bus, in computing, is a set of physical connections (cables, printed circuits, etc.) which can be

shared by multiple hardware components in order to communicate with one another.

The purpose of buses is to reduce the number of "pathways" needed for communication between

the components, by carrying out all communications over a single data channel. This is why the

metaphor of a "data highway" is sometimes used.

If only two hardware components communicate over the line, it is called a hardware port (such

as a serial port or parallel port). A bus is characterised by the amount of information that can be
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transmitted at once. This amount, expressed in bits, corresponds to the number of physical lines

over which data is sent simultaneously. A 32-wire ribbon cable can transmit 32 bits in parallel.

The term "width" is used to refer to the number of bits that a bus can transmit at once.

In reality, each bus is generally constituted of 50 to 100 distinct physical lines, divided into three

subassemblies:

The address bus (sometimes called the memory bus) transports memory addresses which

the processor wants to access in order to read or write data. It is a unidirectional bus.

The data bus transfers instructions coming from or going to the processor. It is a

bidirectional bus.

The control bus (or command bus) transports orders and synchonisation signals coming

from the control unit and travelling to all other hardware components. It is a bidirectional

bus, as it also transmits response signals from the hardware.

21. PROCESSOR

A processor adds, subtracts, multiplies and divides numbers, tests inequalities, etc. The central

processing unit (CPU) is the executive part of the computer, following the instructions of

programs to the letter. In some computers one or more peripheral processors control routine tasks

such as I/O in order toreduce the load on the CPU. A processor is usually classified as 4-, 8-, 16-

or 32-bit, depending on the width of its data bus.

22. CHIPSET

A chipset is the component which routes data between the computer's buses, so that all the

components which make up the computer can communicate with each other. The chipset

originally was made up of a large number of electronic chips, hence the name. It generally has

two components:

The NorthBridge (also called the memory controller) is in charge of controlling transfers

between the processor and the RAM, which is way it is located physically near the

processor. It is sometimes called the GMCH, forrGraphic and Memory Controller Hub.
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The SouthBridge (also called the input/output controller or expansion controller)

handles communications between peripheral devices. It is also called the ICH (I/O

Controller Hub). The tem bridge is generally used to designate a component which

connects two buses.

23. ACCUMULATOR

In a computer's central processing unit (CPU), an accumulator is a register in which

intermediate arithmetic and logic results are stored. Without a register like an accumulator, it

would be necessary to write the result of each calculation (addition, multiplication, shift, etc.) to

main memory, perhaps only to be read right back again for use in the next operation. Access to

main memory is slower than access to a register like the accumulator because the technology

used for the large main memory is slower (but cheaper) than that used for a register.

The characteristic which distinguishes one register as being the accumulator of a computer

architecture is that the accumulator (if the architecture were to have one) would be used as an

implicit operand for arithmetic instructions. For instance, a CPU might have an instruction like:

ADD memaddress
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This instruction would add the value read from the memory location at memaddress to the value

from the accumulator, placing the result in the accumulator. The accumulator is not identified in

the instruction by a register number; it is implicit in the instruction and no other register can be

specified in the instruction. Some architectures use a particular register as an accumulator in

some instructions, but other instructions use register numbers for explicit operand specification

24. INSTRUCTION PIPELINING

In computers, a pipeline is the continuous and somewhat overlapped movement ofinstruction to

the processor or in the arithmetic steps taken by the processor to perform an instruction.

Pipelining is the use of a pipeline. Without a pipeline, a computer processor gets the first

instruction from memory, performs the operation it calls for, and then goes to get the next

instruction from memory, and so forth. While fetching (getting) the instruction, the arithmetic

part of the processor is idle. It must wait until it gets the next instruction. With pipelining, the

computer architecture allows the next instructions to be fetched while the processor is

performing arithmetic operations, holding them in a buffer close to the processor until each

instruction operation can be performed. The staging of instruction fetching is continuous. The

result is an increase in the number of instructions that can be performed during a given time

period.

Computer processor pipelining is sometimes divided into an instruction pipeline and an

arithmetic pipeline. The instruction pipeline represents the stages in which an instruction is

moved through the processor, including its being fetched, perhaps buffered, and then executed.

The arithmetic pipeline represents the parts of an arithmetic operation that can be broken down

and overlapped as they are performed. Pipelines and pipelining also apply to computer memory

controllers and moving data through various memory staging places.

25. ASSOCIATIVE MEMORY

An associative memory is a content addressable structure that maps a set of input patterns to a set

of output patterns. A content addressable structure refers to a memory organization where the
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content is accessed by its content as opposed to an explicit address in the traditional computer

memory system. The associative memory is of two types: auto associative and hetero associative.

An auto associative memory retrieves a previously stored pattern that most closely

resembles the current pattern.

In hetero associative memory, the retrieved pattern is in general different from the

input pattern not only in content but possibly also in type and format.

26. DATA MINING

Data mining (the analysis step of the Knowledge Discovery in Databases process, or KDD), a

relatively young and interdisciplinary field of computer science is the process of discovering new

patterns from large data sets involving methods from statistics and artificial intelligence but

also database management. In contrast to for example machine learning, the emphasis lies on the

discovery ofpreviously unknown patterns as opposed to generalizing known patterns to new data.

Generally, data mining (sometimes called data or knowledge discovery) is the process of

analyzing data from different perspectives and summarizing it into useful information -

information that can be used to increase revenue, cuts costs, or both. Data mining software is one

of a number of analytical tools for analyzing data. It allows users to analyze data from many

different dimensions or angles, categorize it, and summarize the relationships identified.Technically, data mining is the process of finding correlations or patterns among dozens of fields

in large relational databases.

27. RELATIONALDATABASE

The Relational model was first introduces by Dr. Edgar Frank Codd, an oxford-trained

Mathematician, while working in IBM Research Centre in 1970s. He represented this idea in aclassical paper (A Relational Model of Data for Large Shared Data banks) and attracted

immediate attention due to its simplicity and mathematical foundations. The Relational model is

considered one of the most popular developments in the database technology because it can be

used for representing most of the real world objects and the relationships between them.


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Relational Model Terminology

Relation Table

Tuple Row, Record

Attribute Column, Field

Domain Set of Legal Values

Cardinality Number of Rows

Degree Number of Columns

Primary Key Unique Identifier

Foreign Key Identifier used to reference another table

28. DISTRIBUTEDDATABASE

A Distributed database is a single logical database that is spread physically across

computers in multiple locations that are connected by a data communication links. In distributed database the user at any location can access data anywhere in the network as if

the data were all stored at the users own location.

The software that manages the distributed database and provides an access mechanism that

makes this distribution transparent to the user is known as Distributed Database.

Management System (DDBMS):- By the term transparent we mean that the user will be

aware of one relational database schema, it doesnt matter where the data is located or how

the query is executed.

29. QUERY

A query with respect to DBMS relates to user commands that are used to interact with a data

base. The query language can be classified into data definition language and data manipulation

language. The query consists of keywords and data variable which are required for the result.


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30. DBA

DBA is a person or group of persons who is responsible for management of the database.

DBA is a highly skilled person with strong technical background to monitor various

operations such as creating, modifying and maintaining which help in handling three levels

Of the database.

DBA has most of the powers such as defining schemas, storage structures and access

Method strategies, physical organization, authorization and integrity constraints etc.

DBA are the top level authority among all the persons connected to the database.

The main responsibilities of DBA are:

Deciding the information content of the database.

Define the storage structure and access strategies.

Defines external schemas for the users.

Defines integrity constraints specifications.

Granting of authorization for data access.

Define strategy for backup and recovery.

Installing and upgrading the DBMS and the application tools.

Monitoring and optimizing the performance of the database.

Plans the future storage requirements for the database system.

31. RELATIONAL KEYS

The word "key" is much used and abused in the context of relational database design. In pre-

relational databases (hierarchical, networked) and file systems (ISAM, VSAM, et al) "key" oftenreferred to the specific structure and components of a linked list, chain of pointers, or other

physical locator outside of the data. It is thus natural, but unfortunate, that today people often

associate "key" with a RDBMS "index". We will explain what a key is and how it differs from an

index.


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There are only three types of relational keys

Candidate Key

As stated above, a candidate key is any set of one or more columns whose combined values

are unique among all occurrences (i.e., tuples or rows). Since a null value is not guaranteed

to be unique, no component of a candidate key is allowed to be null.

There can be any number of candidate keys in a table Relational pundits are not in

agreement whether zero candidate keys is acceptable, since that would contradict the

(debatable) requirement that there must be a primary key.

Primary Key

The primary key of any table is any candidate key of that table which the database designer

arbitrarily designates as "primary". The primary key may be selected for convenience,

comprehension, performance, or any other reasons. It is entirely proper (albeit often

inconvenient) to change the selection of primary key to another candidate key.

Alternate Key

The alternate keys of any table are simply those candidate keys which are not currently

selected as the primary key. According to {Date95} "... exactly one of those candidate keys

[is] chosen as the primary key [and] the remainder, if any, are then called alternate keys."

An alternate key is a function of all candidate keys minus the primary key.

32. ENTITY RELATIONSHIP DIAGRAM

An entity-relationship (ER) diagram is a specialized graphic that illustrates the relationships

between entities in a database. ER diagrams often use symbols to represent three different types

of information. Also Known As: ER Diagram, E-R Diagram, entity-relationship model.

Such a diagram consists of the following major components:

Rectangles, which represent entity sets

Ellipses, which represent attributes

Diamonds, which represent relationship sets

Lines, which link attributes to entity sets and entity sets to relationship sets

Double ellipses, which represent multivalued attributes

Dashed ellipses, which denote derived attributes


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Double lines, which indicate total participation of an entity in a relationship set

Double rectangles, which represent weak entity sets

Examples:

Consider the example of a database that contains information on the residents of a city. The ER

diagram shown in the image above contains two entities -- people and cities. There is a single

"Lives In" relationship. In our example, due to space constraints, there is only one attribute

associated with each entity. People have names and cities have populations. In a real-world

example, each one of these would likely have many different attributes.

33. DATABASE REPLICATION

Database replication can be used on many database management systems, usually with a

master/slave relationship between the original and the copies. The master logs the updates, which

then ripple through to the slaves. The slave outputs a message stating that it has received the

update successfully, thus allowing the sending (and potentially re-sending until successfully

applied) of subsequent updates. Multi-master replication, where updates can be submitted to any

database node, and then ripple through to other servers, is often desired, but introduces

substantially increased costs and complexity which may make it impractical in some situations.

The most common challenge that exists in multi-master replication is transactional conflict

prevention or resolution. Most synchronous or eager replication solutions do conflict prevention,

while asynchronous solutions have to do conflict resolution. For instance, if a record is changed

on two nodes simultaneously, an eager replication system would detect the conflict before

confirming the commit and abort one of the transactions. A lazy replication system would allow

both transactions to commit and run a conflict resolution during resynchronization. The


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resolution of such a conflict may be based on a timestamp of the transaction, on the hierarchy of

the origin nodes or on much more complex logic, which decides consistently on all nodes.

Database replication becomes difficult when it scales up. Usually, the scale up goes with two

dimensions, horizontal and vertical: horizontal scale up has more data replicas, vertical scale up

has data replicas located further away in distance. Problems raised by horizontal scale up can be

alleviated by a multi-layer multi-view access protocol. Vertical scale up is running into less

trouble since internet reliability and performance are improving.

34. NORMALIZATION:

In the design of a relational database management system (RDBMS), the process of organizing

data to minimize redundancy is called normalization. The goal of database normalization is to

decompose relations with anomalies in order to produce smaller, well-structured relations.

Normalization usually involves dividing large tables into smaller (and less redundant) tables and

defining relationships between them. The objective is to isolate data so that additions, deletions,

and modifications of a field can be made in just one table and then propagated through the rest of

the database via the defined relationships.

35. CLIENT/SERVER

Client/server describes the relationship between two computer programs in which one

program, the client, makes a service request from another program, the server, which fulfils

the request.

Although the client/server idea can be used by programs within a single computer, it is a

more important idea in a network. In a network, the client/server model provides a

convenient way to interconnect programs that are distributed efficiently across different

locations. In the usual client/server model, one server, sometimes called a daemon, is

activated and awaits client requests.


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The clients make requests to the server and the server responds to the requests.

36. COMMIT

In Oracle changes you make to your data are not permanent until you tell Oracle to make

them so. This is accomplished using a SQL statement known as Commit.

A Commit ends your transaction and makes the changes you have made permanent.

The syntax is:

SQL>COMMIT;

The following points should be remembered while using COMMIT statement.

Whenever you execute a DDL statement (such as CREATE TABLE etc.) an implicit commit

statement is generated before and after it is executed, even if the DDL fails. This is not in the

case of DML statements.

The Commit statement that one user issues have no effect on another users database

changes.

37. DATABASE

Database can be defined as A well organized collection of data that are related in a

meaningful way which can be accessed by different users but stored only once.


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Consider an example of telephone directory in which names/surnames of a person is arranged

in an alphabetical order. So it becomes easier to search any phone number corresponding to a

particular name. If this ordering is not done in an organized manner then it is very difficult to

search a phone number of a particular person, so this shows why databases are needed.

Features of data in a Database

It should be well organized.

It should be related.

It should be integrated or in other words it should be correct.

It should represent the relationship with the real world.

It should be shared among different users as well as applications. It should be stored permanently so that it can be used later on.

It should be available when and where it is needed i.e. it should be accessible.

It should be secured from the unauthorized users access.

It should be stored only once and can be used again and again whenever it is required.

It should be flexible to change.

38. DATA DICTIONARY

Data dictionary is a respiratory of description of data in the database.

It contains information about Data Names of the tables, names of attributes of each

table, length of attributes etc. Relationship between database transactions and data items

referenced by them which is useful in determining which transactions are effected when

certain data definitions are changed.

Constraints on the data i.e. range of values permitted.

Detailed information on physical database design.

Description of database users, their responsibilities and access rights.

Every Oracles database has a data dictionary; it is catalog of your entire Oracle database objects.

As you create users, tables constraints and other database objects, Oracle automatically

maintains a catalog of items stored in the data base.


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Some of the examples are:

USER_ CONSTRAINTS: The view used to see the constraints associated with the table.

USER_TABLES: This view used to show information about the tables owned by the

user.

ALL_TABLES: this view is used to show information that you own and also the tables

that you have been granted.

ALL_USERS: this view is used to show all the usernames, User_ID and their date of

creation.

39. DATA INDEPENDENCE

Data independence means that the application is independent of the storage structure and

access strategy of data.

In other words, the ability to modify the schema definition in one level should not affect the

schema definition in the next higher level. Data independence is the type of data transparency

that matters for a centralized DBMS.

It refers to the immunity of user applications to make changes in the definition and

organization of data.

Physical data independence deals with hiding the details of the storage structure from user

applications. The application should not be involved with these issues, since there is no

difference in the operation carried out against the data.

The data independence and operation independence together gives the feature of data

abstraction. There are two levels of data independence.

Two types of Data Independence:

Physical Data Independence: The capacity to change the conceptual schema without

having to change the external schemas and their application programs.

Logical Data Independence :The capacity to change the internal schema without having

to change the conceptual schema.


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40. DBMS

It is a collection of programs that enables user to create and maintain a database. In other words

it is general-purpose software that provides the users with the processes of defining, constructing

and manipulating the database for various applications. A Database Management System

(DBMS) is a set ofcomputer programs that controls the creation, maintenance, and the use of the

database with computer as a platform or of an organization and its end users. It allows

organizations to place control of organization-wide database development in the hands of

database administrators (DBAs) and other specialists. A DBMS is a system software package

that helps the use of integrated collection of data records and files known as databases. It allows

different user application programs to easily access the same database. DBMSs may use any of a

variety ofdatabase models, such as the network model or relational model. In large systems, aDBMS allows users and other software to store and retrieve data in a structured way. Instead of

having to write computer programs to extract information, user can ask simple questions in a

query language. It helps to specify the logical organization for a database and access and use the

information within a database. It provides facilities for controlling data access, enforcing data

integrity, managing concurrency controlled, and restoring database. A DBMS is a set ofsoftware

programs that controls the organization, storage, management, and retrieval ofdata in a database.

DBMSs are categorized according to their data structures or types.

41. VIEWS

A view may be thought of as a virtual table, that is, a table that does not really exist in its own

right but is instead derived from one or more underlying base table. In other words, there is no

stored file that direct represents the view instead a definition of view is stored in data dictionary.

Growth and restructuring of base tables is not reflected in views. Thus the view can insulate

users from the effects of restructuring and growth in the database. Hence accounts for logical

data independence.

Views can provide advantages over tables:

Views can represent a subset of the data contained in a table

Views can join and simplify multiple tables into a single virtual table
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Views can act as aggregated tables, where the database engine aggregates data (sum,

average etc) and presents the calculated results as part of the data

Views take very little space to store; the database contains only the definition of a view,

not a copy of all the data it presents

Depending on the SQL engine used, views can provide extra security

Views can limit the degree of exposure of a table or tables to the outer world.

42. DATA MODEL

A data is an abstract model that describes how data is represented and accessed. Data models

formally define data elements and relationships among data elements for a domain of interest.

Data model explicitly determines the meaning of data, which in this case is known as structured

data (as opposed to unstructured data, for example an image, a binary file or a natural language

text, where the meaning has to be elaborated). Typical applications of data models include

database models, design of information systems, and enabling exchange of data. Usually data

models are specified in a data modeling language. A data model can be sometimes referred to as

a data structure, especially in the context of programming languages. Data models are often

complemented by function models, especially in the context ofenterprise models.

A data model is a way finding tool for both business and IT professionals, which uses a set of

symbols and text to precisely explain a subset of real information to improve communication

within the organization and thereby lead to a more flexible and stable application environment.

Communication and precision are the two key benefits that make a data model important to

applications that use and exchange data. A data model is the medium which project team

members from different backgrounds and with different levels of experience can communicate

with one another. Precision means that the terms and rules on a data model can be interpreted

only one way and are not ambiguous

The main aim of data models is to support the development of information systems by providing

the definition and format of data. According to West and Fowler (1999) "if this is done
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consistently across systems then compatibility of data can be achieved. If the same data

structures are used to store and access data then different applications can share data.

43. TRANSACTION

A transaction is a unit of program execution that accesses and possibly updates various data

items. Usually, a transaction is initiated by a user program written in a high-level data

manipulation language or programming language (for example, SQL, COBOL, C, C++, or Java),

where it is delimited by statements (or function calls) of the form begin transaction and end

transaction. The transaction consists of all operations executed between the begin transaction and

end transaction.

To ensure integrity of the data, we require that the database system maintain the following

properties of the transactions:

Atomicity. Either all operations of the transaction are reflected properly in the database, or

none are.

Consistency. Execution of a transaction in isolation (that is, with no other transaction

executing concurrently) preserves the consistency of the database.

Isolation. Even though multiple transactions may execute concurrently, the system guarantees

that, for every pair of transactions Ti and Tj , it appears to Ti that either Tj finished executionbefore Ti started, or Tj started execution after Ti finished. Thus, each transaction is unaware of

other transactions executing concurrently in the system.

Durability. After a transaction completes successfully, the changes it has made to the database

persist, even if there are system failures.

These properties are often called the ACID properties; the acronym is derived from the first

letter of each of the four properties.

44. SQL

SQL (Structured Query Language) is a standard interactive and programming language for

getting information from and updating a database. Although SQL is both an ANSI and an ISO

standard, many database products support SQL with proprietary extensions to the standard
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language. Queries take the form of a command language that lets you select, insert, update, find

out the location of data, and so forth. There is also a programming interface.

The SQL language has several parts:

Data-definition language (DDL). The SQL DDL provides commands for defining relation

schemas, deleting relations, and modifying relation schemas.

Interactive data-manipulation language (DML). The SQL DML includes a query language

based on both the relational algebra and the tuple relational calculus. It includes also commands

to insert tuples into, delete tuples from, and modify tuples in the database.

View definition. The SQL DDL includes commands for defining views.

Transaction control. SQL includes commands for specifying the beginning and ending of

transactions.

Embedded SQL and dynamic SQL. Embedded and dynamic SQL define how SQL statements

can be embedded within general-purpose programming languages, such as C, C++, Java, PL/I,

Cobol, Pascal, and Fortran.

Integrity. The SQL DDL includes commands for specifying integrity constraints that the data

stored in the database must satisfy. Updates that violate integrity constraints are disallowed.

Authorization. The SQL DDL includes commands for specifying access rights to relations and

views.

45. DECISION SUPPORT SYSTEM

Decision support is methodology (or series of methodologies) designed to extract information

from data and to use such information as a basis for decision making

Decision support system (DSS) is

Arrangement of computerized tools used to assist managerial decision making within

business

Usually requires extensive data massaging to produce information

Used at all levels within organization

Often tailored to focus on specific business areas

Provides ad hoc query tools to retrieve data and to display data in different formats


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46. ENTITY

It is a 'thing' in the real world with an independent existence. An entity is something that has a

distinct, separate existence, though it need not be a material existence. In particular, abstractions

and legal fictions are usually regarded as entities. In general, there is also no presumption that an

entity is animate. Entities are used in system developmental models that display communications

and internal processing of, say, documents compared to order processing. An entity could be

viewed as a set containing subsets. In philosophy, such sets are said to be abstract objects.

Sometimes, the word entity is used in a general sense of a being, whether or not the referent has

material existence; e.g., is often referred to as an entity with no corporeal form, such as a

language. It is also often used to refer to ghosts and other spirits. Taken further, entity sometimes

refers to existence or being itself.

An entity may be a physical object such as a house or a car, an event such as a house sale or a car

service, or a concept such as a customer transaction or order. Although the term entity is the one

most commonly used, following Chen we should really distinguish between an entity and an

entity-type. An entity-type is a category. An entity, strictly speaking, is an instance of a given

entity-type. There are usually many instances of an entity-type. Because the term entity-type is

somewhat cumbersome, most people tend to use the term entity as a synonym for this term.

An entity with an attribute

47. DATABASE SCHEMA

Databases change over time as information is inserted and deleted. The collection of information

stored in the database at a particular moment is called an instance of the database. The overall

design of the database is called the database schema. Schemas are changed infrequently, if at all.
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Database systems have several schemas, partitioned according to the levels of abstraction. The

physical schema describes the database design at the physical level, while the logical schema

describes the database design at the logical level.A database may also have several schemas at

the view level, sometimes called subschemas, that describe different views of the database. Of

these, the logical schema is by far the most important, in terms of its effect on application

programs, since programmers construct applications by using the logical schema. The physical

schema is hidden beneath the logical schema, and can usually be changed easily without

affecting application programs. Application programs are said to exhibit physical data

independence if they do not depend on the physical schema, and thus need not be rewritten if the

physical schema changes.

48. INDEX

An index can be created in a table to find data more quickly and efficiently.The users cannot see

the indexes, they are just used to speed up searches/queries.

SQL CREATE INDEX Syntax

Creates an index on a table. Duplicate values are allowed:

CREATE INDEX index_name ON table_name (column_name)

SQL CREATE UNIQUE INDEX Syntax

Creates a unique index on a table. Duplicate values are not allowed:

CREATE UNIQUE INDEX index_name ON table_name (column_name)

49. CONCURRENCY CONTROL

When many people attempt to modify data in a database at the same time, a system of controls

must be implemented so that modifications made by one person do not adversely affect those of

another person. This is called concurrency control.


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Concurrency control theory has two classifications for the methods of instituting concurrency

control:

Pessimistic concurrency control

A system of locks prevents users from modifying data in a way that affects other users.

After a user performs an action that causes a lock to be applied, other users cannot perform

actions that would conflict with the lock until the owner releases it. This is called

pessimistic control because it is mainly used in environments where there is high

contention for data, where the cost of protecting data with locks is less than the cost of

rolling back transactions if concurrency conflicts occur.

Optimistic concurrency control

In optimistic concurrency control, users do not lock data when they read it. When a user

updates data, the system checks to see if another user changed the data after it was read. If

another user updated the data, an error is raised. Typically, the user receiving the error

rolls back the transaction and starts over. This is called optimistic because it is mainly used

in environments where there is low contention for data, and where the cost of occasionally

rolling back a transaction is lower than the cost of locking data when read.

50. HIERARCHICAL DATABASE MODEL

A hierarchical database model is a data model in which the data is organized into a tree-like

structure. The structure allows representing information using parent/child relationships: each

parent can have many children, but each child has only one parent (also known as a 1-to-many

relationship). All attributes of a specific record are listed under an entity type.

Example of an hierarchical model:

In a database an entity type is the equivalent of a table. Each individual record is represented as a

row, and each attribute as a column. Entity types are related to each other using 1:Nmappings,
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also known as one-to-many relationships. This model is recognized as the first database model

created by IBM in the 1960s.

51. FTP

File Transfer Protocol is a standard network protocol used to transfer files from one host to

another over a TCP-based network, such as the Internet. FTP is built on client-server architecture

and utilizes separate control and data connections between the client and server.FTP users may

authenticate themselves using a clear-text sign-in protocol but can connect anonymously if the

server is configured to allow it.

As a user, you can use FTP with a simple command line interface (for example, from the

Windows MS-DOS Prompt window) or with a commercial program that offers a graphical user

interface. Your Web browser can also make FTP requests to download programs you select from

a Web page. Using FTP, you can also update (delete, rename, move, and copy) files at a server.

You need to logon to an FTP server. However, publicly available files are easily accessed using

anonymous FTP.

52. TOPOLOGY

The physical topology of a network refers to the configuration of cables, computers, and other

peripherals. Physical topology should not be confused with logical topology which is the method

used to pass information between workstations.
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There are many types of topologies depending upon their architecture:

Bus Topology

Star Topology

Ring Topology

Mesh Topology

Hybrid Topology

53. TRANSMISSION MEDIA

A transmission medium (plural transmission media) is a material substance that can propagate

energy waves. For example, the transmission medium for sound received by the ears is usually

air, but solids and liquids may also act as transmission media for sound.The term transmission

medium also refers to a technical device that employs the material substance to transmit or guide

waves. Thus, an optical fiber or a copper cable is a transmission medium.

A transmission medium can be classified as a:

Linear medium, if different waves at any particular point in the medium can be superposed.

Bounded medium, if it is finite in extent, otherwise unbounded medium; Uniform medium or homogeneous medium, if its physical properties are unchanged at

different points;

Isotropic medium, if its physical properties are the same in different directions.

54. TWISTED PAIR CABLE

Twisted pair cabling is a type of wiring in which two conductors (the forward and return

conductors of a single circuit) are twisted together for the purposes of canceling out electro

magnetic interference (EMI) from external sources; for instance, electromagnetic radiation from

unshielded twisted pair (UTP) cables, and crosstalkbetween neighboring pairs. It was invented

by Alexander Graham Bell.
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A type of cable that consists of two independently insulated wires twisted around one another.

The use of two wires twisted together helps to reduce crosstalkand electromagnetic induction.

While twisted-pair cable is used by older telephone networks and is the least expensive type

oflocal-area network (LAN) cable, most networks contain some twisted-pair cabling at some

point along the network. Other types of cables used for LANs include coaxial cables and fiber

optic cables.

55. ASYNCHRONOUS TRANSMISSION

In Asynchronous transmission, data is transmitted character by character at irregular

intervals. That is, a sender sends a character at any convenient manner and receiver accepts

it.

For instance, transmission of data from a terminal to a computer is asynchronous because

during data entry by an operator, time between successive keystrokes varies.

To enable a receiver to recognize a character when it arrives, a transmitter frames each

character by putting a start bit before it and one or two( depending upon system) stop bits

after it.

Asynchronous transmission is well suited to many input devices. Its advantage is that it does

not require any local storage at sender or receiver end, because transmission takes place

character by character. Hence, it is cheaper to implement.

56. TCP/IP
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TCP- (Transmission Internet Protocol) is responsible for verifying the correct delivery of data

from client to server. Data can be lost in the intermediate network. TCP adds support to detect

errors or lost data and to trigger retransmission until the data is correctly and completely

received.

IP- (Internet protocol) is responsible for moving packet of data from node to node. IP forwards

each packet based on a four byte destination address (the IP number). The Internet authorities

assign ranges of numbers to different organizations. The organizations assign groups of their

numbers to departments. IP operates on gateway machines that move data from department to

organization to region and then around the world.

57. BITRATE

Bit rate, as the name implies, describes the rate at which bits are transferred from one location to

another. In other words, it measures how much data is transmitted in a given amount of time. Bit

rate is commonly measured in bits per second (bps), kilobits per second (Kbps), or megabits per

second (Mbps). For example, a DSL connection may be able to download data at 768 kbps,

while a Fire wire 800 connection can transfer data up to 800 Mbps.

Bit rate can also describe the quality of an audio or video file. For example, an MP3 audio file

that is compressed at 192 Kbps will have a greater dynamic range and may sound slightly more

clear than the same audio file compressed at 128 Kbps. This is because more bits are used to

represent the audio data for each second of playback. Similarly, a video file that is compressed at

3000 Kbps will look better than the same file compressed at 1000 Kbps. Just like the quality of

an image is measured in resolution, the quality of an audio or video file is measured by the bit

rate.

58. GOPHER

A system that pre-dates the World Wide Web for organizing and displaying files on Internet

servers. A Gopher server presents its contents as a hierarchically structured list of files. With the


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ascendance of the Web, many gopher databases were converted to Web sites which can be more

easily accessed via Web search engines.

The Gopher protocol is a TCP/IP application layer protocol designed for distributing,

searching, and retrieving documents over the Internet .Strongly oriented towards a menu-

document design, the Gopher protocol was a predecessor of (and later, an alternative to) the

World Wide Web.

59. ATM

Stands for "Asynchronous Transfer Mode". Most people know of ATMs as automated teller

machines -- those friendly boxes that allow you to withdraw cash from your bank or credit

account while charging you a ridiculous surcharge for the service. In the computer world,

however, ATM has a different meaning. Asynchronous Transfer Mode is a networking

technology that transfers data in packets or cells of a fixed size.

ATM uses 53-byte cells (5 bytes for the address header and 48 bytes for the data). These

extremely small cells can be processed through an ATM switch (not an automated teller

machine) fast enough to maintain data transfer speeds of over 600 mbps. The technology was

designed for the high-speed transmission of all forms of media from basic graphics to full-

motion video. Because the cells are so small, ATM equipment can transmit large amounts of data

over a single connection while ensuring that no single transmission takes up all the bandwidth. It

also allows Internet Service Providers (ISPs) to assign limited bandwidth to each customer.

While this may seem like a downside for the customer, it actually improves the efficiency of the

ISP's Internet connection, causing the overall speed of the connection to be faster for everybody.

60. DATATRANSFERRATE

The data transfer rate is commonly used to measure how fast data is transferred from one

location to another. For example, a hard drive may have a maximum data transfer rate of 480


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Mbps, while your ISP may offer an Internet connection with a maximum data transfer rate of

only 1.5 Mbps.

Data transfer rates are typically measured in bits per second (bps) as opposed to bytes per

second, which can be understandably confusing. Because there are eight bits in a byte, a

sustained data transfer rate of 80 Mbps is only transferring 10MB per second. While this is

confusing for consumers, Internet service providers must enjoy measuring data transfer rates in

bps since it makes their Internet access speeds sound 8 x faster than they really are.

61. EXTRANET

Extranets are networks that connect companies with customers and partners.

In Extranet a company has to work with the other like-minded organizations on the

network, so that it is accessible to specific people or groups outside the organization.

Extranets require more security and technical consideration because they have to send

private information securely over public networks.

Extranets provides a safe way to allow transactional business-to-business activities.

Extranet is more complex and costly to set up and requires efficient internal systems.

Example of Extranet:-

Different banks are providing the facility of ATM (Automatic Teller Machine) cards with VISA

facility means one can make use of HDFC ATM in ICICI ATM machine anywhere in the world.

62. INTRANET

An Intranet is a network within an organization uses technology similar to internet that

enables users to find, use, share documents and web pages.

Corporations use intranet to communicate with employees.

In large companies, Intranet is being used by employees to obtain and share work-related

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learning tools and learn about company news. Any message from company broadcast to all

computers.

Intranets use traditional Internet protocols TCP/IP and HTTP to transfer data.

Advantages of Intranet:-

Intranet is based on Internet technologies and protocols. That means Intranet can make

use of all the facilities of Internet.

Intranet information is accessible using GUI based interface provided by web browsers.

You can use the browsers such as Internet Explorer and Netscape Navigator.

Intranets are easier and less expensive to setup and maintain than traditional networks.

Documents on Intranet are written in HTML. One can produce HTML documents using

Microsoft Word by saving the document as a web page.

Since Intranets are based on Internet technology, they can also incorporate graphics,

sound and video, e-mail, newsgroups facilities.

Staff will find it simpler and more intuitive to use because it is accessed through a web

browser provides an easy, point and click interface.

An Intranet does not mean interconnection of a lot of people. Depending on your

business need, it could link just 3 or 4 people in your organization.

63. MULTIPLEXER

In telecommunications and computer networks, multiplexing (also known as muxing) is a

method by which multiple analog message signals or digital data streams are combined into one

signal over a shared medium. The aim is to share an expensive resource. For example, in

telecommunications, several telephone calls may be carried using one wire. Multiplexing

originated in telegraphy, and is now widely applied in communications.

The multiplexed signal is transmitted over a communication channel, which may be a physical

transmission medium. The multiplexing divides the capacity of the low-level communication

channel into several higher-level logical channels, one for each message signal or data stream to
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be transferred. A reverse process, known as demultiple

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