Thursday, 13 December 2012

Computer network

A computer network, or simply a network, is a collection of computers and other hardware interconnected by communication channels that allow sharing of resources and information.[1] Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network. A network is a group of devices connected to each other. Networks may be classified into a wide variety of characteristics, such as the medium used to transport the data, communications protocol used, scale, topology, benefit, and organizational scope.

Communications protocols define the rules and data formats for exchanging information in a computer network, and provide the basis for network programming. Well-known communications protocols include two Ethernet, a hardware and link layer standard that is ubiquitous in local area networks, and the Internet protocol suite, which defines a set of protocols for internetworking, i.e. for data communication between multiple networks, as well as host-to-host data transfer, and application-specific data transmission formats.

Computer networking is sometimes considered a sub-discipline of electrical engineering, telecommunications, computer science, information technology or computer engineering, since it relies upon the theoretical and practical application of these disciplines.


Computer networks:

Facilitate communications 
    Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.
Permit sharing of files, data, and other types of information
    In a network environment, authorized users may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.
Share network and computing resources
    In a networked environment, each computer on a network may access and use resources provided by devices on the network, such as printing a document on a shared network printer. Distributed computing uses computing resources across a network to accomplish tasks.

May be insecure
    A computer network may be used by computer hackers to deploy computer viruses or computer worms on devices connected to the network, or to prevent these devices from normally accessing the network (denial of service).
May interfere with other technologies
    Power line communication strongly disturbs certain forms of radio communication, e.g., amateur radio. It may also interfere with last mile access technologies such as ADSL and VDSL.
May be difficult to set up
    A complex computer network may be difficult to set up. It may also be very costly to set up an effective computer network in a large organization or company. 

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Tuesday, 11 December 2012

Theory of Computation

In theoretical computer science and mathematics, the theory of computation is the branch that deals with whether and how efficiently problems can be solved on a model of computation, using an algorithm. The field is divided into three major branches: automata theory, computability theory and computational complexity theory.

In order to perform a rigorous study of computation, computer scientists work with a mathematical abstraction of computers called a model of computation. There are several models in use, but the most commonly examined is the Turing machine. Computer scientists study the Turing machine because it is simple to formulate, can be analyzed and used to prove results, and because it represents what many consider the most powerful possible "reasonable" model of computation (see Church–Turing thesis). It might seem that the potentially infinite memory capacity is an unrealizable attribute, but any decidable problem solved by a Turing machine will always require only a finite amount of memory. So in principle, any problem that can be solved (decided) by a Turing machine can be solved by a computer that has a bounded amount of memory.


The theory of computation can be considered the creation of models of all kinds in the field of computer science. Therefore mathematics and logic are used. In the last century it became an independent academic discipline and was separated from mathematics.
Some pioneers of the theory of computation were Alonzo Church, Alan Turing, Stephen Kleene, John von Neumann and Claude Shannon.


Automata theory

Automata theory is the study of abstract machines (or more appropriately, abstract 'mathematical' machines or systems) and the computational problems that can be solved using these machines. These abstract machines are called automata. Automata comes from the Greek word (Αυτόματα)which means that something is doing something by itself. Automata theory is also closely related to formal language theory, as the automata are often classified by the class of formal languages they are able to recognize. An automaton can be a finite representation of a formal language that may be an infinite set.

Computability theory

Computability theory deals primarily with the question of the extent to which a problem is solvable on a computer. The statement that the halting problem cannot be solved by a Turing machine is one of the most important results in computability theory, as it is an example of a concrete problem that is both easy to formulate and impossible to solve using a Turing machine. Much of computability theory builds on the halting problem result.
Another important step in computability theory was Rice's theorem, which states that for all non-trivial properties of partial functions, it is undecidable whether a Turing machine computes a partial function with that property.
Computability theory is closely related to the branch of mathematical logic called recursion theory, which removes the restriction of studying only models of computation which are reducible to the Turing model. Many mathematicians and computational theorists who study recursion theory will refer to it as computability theory.

Computational complexity theory

Complexity theory considers not only whether a problem can be solved at all on a computer, but also how efficiently the problem can be solved. Two major aspects are considered: time complexity and space complexity, which are respectively how many steps does it take to perform a computation, and how much memory is required to perform that computation.
In order to analyze how much time and space a given algorithm requires, computer scientists express the time or space required to solve the problem as a function of the size of the input problem. For example, finding a particular number in a long list of numbers becomes harder as the list of numbers grows larger. If we say there are n numbers in the list, then if the list is not sorted or indexed in any way we may have to look at every number in order to find the number we're seeking. We thus say that in order to solve this problem, the computer needs to perform a number of steps that grows linearly in the size of the problem.

To simplify this problem, computer scientists have adopted Big O notation, which allows functions to be compared in a way that ensures that particular aspects of a machine's construction do not need to be considered, but rather only the asymptotic behavior as problems become large. So in our previous example we might say that the problem requires  steps to solve.
Perhaps the most important open problem in all of computer science is the question of whether a certain broad class of problems denoted NP can be solved efficiently. This is discussed further at Complexity classes P and NP.


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Friday, 10 August 2012

Basic Computer Structure and Knowledge Basic Computer Structure

1. Logical Structure of a computer includes:

  •  BIOS (The Basic Input Output System)
  •  CPU (The Processor)
  •  Memory / RAM (Temporary Storage)
  •  Hard Disk (Permanent Storage)
  •  Input / Output Device
  •  Communication Channel (Eg. USB)
  •  Bus (High Speed Internal Communication)
  •  Other Add-on Device…
Example of a Computer Structure


  •  Basic Input Output System
  •  Store all the parameter before the OS Load (Example are Hard Disk Size, Memory   Speed, Turn on or turn off the build in device  such as Sound Card, USB, printer etc)
  • Usually stored in Flash Memory

One of the BIOS Screen Dump

Identify the Component - CPU

  •    Central Processing Unit
  •   .It is the core of a computer.  Responsible for all the   calculation and part of the video.
  •  Usually in the Speed of GHz
  •  1G around 1,000 MHz
  •  1M = 1Million Instruction / second Some Expensive CPU have   more build in memory (Cache   Memory)

How to Choose a CPU 

  •  Mainly AMD / Intel Dominate the Market.
  • .In the current market you have several categories of   microprocessors to choose for your desktop   computers: Xeon, Pentium IV, Celeron, Dual Core,  Quad Core, Athlon, and AMDX64 etc.
  • .Price vs. Performance: There is typically no good correlation between these two factors, especially at the top speeds. Average users should not purchase the top-speed on the market. The price difference is not worthy of the performance difference.
  • . Based on your budget, find a suitable CPU.

Memory / RAM

  •  RAM – Random Access Memory
  •  Act as a temporary Storage.
  •  EDO > SDRAM > DDR > DDR2 
  •  All data stored in memory are volatile. (Need electricity to keep the data)
  •  Memory Size is around 256M / 512M / 1G / 2G per memory module
  •  Basic Configuration is around 512M RAM

Hard Disk (ATA / SATA / SCSI)

  •  Used to stored data permanently.
  •  Different Type of Hard Disk Size (3.5”,  2.5”,  1.8”, Micro Drive)
  •  Different Interface : ATA / SATA / SCSI(Speed : ATA < SATA < SCSI)
  •  Different Speed (Mechanical)(4,200rpm / 5,400rpm /7,200rpm / 10,000 rpm )

Hard Disk (ATA / SATA / SCSI) – Cond.

  • Different Build in Memory Size(2M / 8M / 16M etc
  •  Different Capacity(80G to 500G or even 1T)
  •  Small Size Hard Disk are more popular as they are portable size.

Main Board / Mother Board (MB)

  •  Provide a platform to connecting all the devices.(Keyboard / Mouse / Power / CPU / Memory / Hard Disk / Floppy Disk / Display Card etc)
  •  Many Main Board has already build in Sound Card / Network Card or even display card.

I/O Device & Interface

  •  ATA / SATA /SCSI (For Hard Disk)
  •  Parallel Port or LPT Port (For Printer)
  •  COM Port (For Modem)
  •  RJ45 Socket (For Network)
  •  PS/2 (For Keyboard / Mouse)
  •  D-Sub / DVI (For Monitor)
  •  USB (All compatible device)

Power Supply
  •  Power Supply Convert the  A.C. Voltage to Lower D.C. Voltage which is suitable for Computer.
  •  Power Supply can be classified by their loading (Watt).
  •  Different type of socket for different device.Case
  • Case is used to place the main board and the power supply.
  • Most case have  external USB connection.

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