COM111 Lecture Schedule 2

COM111 Lecture Schedule 2

The Computer System, Computer Organization and Architecture, Central Processing Unit, Inside a Computer

Computer System

            Every computer needs to be instructed exactly what to do and how to do. The instructions given to computers are called as programs. The parts of the computers are classified into two major categories such as hardware (All Physical parts) and software (All information or data).

Hardware:

The physical parts that make up a computer (CPU, input, output and storage) are known as hardware. Any hardware device connected to the computer or any part of the computer outside the CPU and working memory is known as peripheral. Examples of peripherals are keyboards, mouse and monitors.

Software:

            The user issues instructions and the CPU acts in accordance with the instructions. The sets of instructions, which control the sequence of operations, are known as programs, and collectively programs are called software.

Computer Organization and Architecture

A computer is designed using four basic units:

·       Central Processing Unit

·       Input Unit

·       Output Unit

·       Storage/Memory Unit

Central Processing Unit (CPU):

            The CPU, is also known as a processor, is the brain of the computer system that processes data (input) and converts it into meaningful information (output). It is referred to as the administrative section of the computer system. CPU works with data in discrete form that is either 1 or 0. In addition, it contro0ls the usage of the main memory to store data and instructions, and controls the sequence of operations. The CPU itself has three subsystems, The i)arithmetic /logic unit ii)the control unit and iii)the registers. The three subsystems work together to provide operational capabilities to a computer.

Arithmetic/logic Unit (ALU): Arithmetic/logic Unit (ALU) contains the electronic circuitry that executes and performs all the arithmetic(add, subtract) and logical operations(and, or) on the data made available to it. ALU comprises of two units: Arithmetic Unit(AU) and Logic Unit(LU).

Arithmetic Unit(AU): The AU contains the circuitry that is responsible for performing the actual computing and carrying out arithmetic calculations such as addition , subtraction, Multiplication and Division. It can perform these operations at a very high speed.

Logic Unit(LU): The LU enables the CPU to make logical operations based on the instructions provided to it. These operations are logical comparisons between data items. The LU can compare numbers, letters or special characters and then take action based on the result of the comparison. Logical operations of the LU test for three conditions:

·        Equal-to condition: In a test for this condition, the ALU compares two values to determine if they are equal.

·        Less than condition: To test this condition ,the ALU compares two values to determine if one is less than the other.

·        Greater than condition: To test this condition  the ALU compares two values to determine if one is greater than the other.

Control Unit: This unit checks the correctness of the sequence of operations. It also controls the I/O devices and directs the overall functioning of the other units of the computer.

Registers: These are the special-purpose, high-speed temporary memory units that can hold varied information such as data, instructions, addresses and intermediate results of calculations. The registers can be considered as the CPU’s working memory, an additional storage location that provides the advantage of speed.

INPUT UNIT:

            An input unit accepts instructions and data from the user with help of input devices such as keyboard, mouse, light pen etc. The input unit converts the data and instructions into the form that the computer can understand. After this, the input unit supplies the converted instructions and data to the computer for further processing.

OUTPUT UNIT:

            The output unit performs just opposite to that of input unit. It accepts the output(which is in machine coded form)produced by the computer, converts them into the user understandable form and supplies the converted results to the user with the help of an output device.

STORAGE/MEMORY UNIT:

            The storage unit of a computer comprises two types of memory/storage. They are primary memory and secondary memory.

Primary Memory:

            The primary memory, also called the main memory, is the part of a computer holds the instructions and data currently being processed by the CPU, the intermediate results produces during the course of calculations and the recently processed data. While the instructions and data remain in the main memory, the CPU can access them directly and quickly. However, the primary memory is quite expensive and has a limited storage capacity.

Secondary Memory:

            Due to the limited size of the primary memory, a computer employs the secondary memory, which is extensively used for storing data and instructions. It is less expensive and has higher storage capacity than the primary memory. Some commonly used secondary storage devices are floppy disk, hard disks and tape drives.

Input/output Devices

The user interacts with the computer via I/O unit. The Input unit accepts data from the user and the Output unit provides the processed data i.e. the information to the user.

Input Devices

Input device is a hardware device that sends information to the computer.

Mouse: Mouse is a pointer device. The mouse allows an  individual to control a pointer in a graphical user interface (GUI).  Utilizing a mouse a user has the ability to per-form various functions such as opening a program or file and does not require the user to memorize commands.
Digital camera: A type of camera that stores the pictures or video it takes in electronic format instead of to film.
Web Cam: A camera connected to a computer that allows anyone connected to the Internet to view still pictures or motion video of a user.
Joystick: A computer joystick allows an individual to easily navigate an object in a game such as navigating a plane in a flight simulator.
Keyboard: One of the main input devices used on a computer, a computer keyboard looks very similar to the keyboards of electric typewriters, with some additional keys.. QWERTY, AZERTY, Dvorak are the dif­ferent types of keyboards.
Microphone Sometimes abbreviated as mic, a mi­crophone is a hardware peripheral that allows computer users to input audio into their computers.
Scanner Input device that allows a user to take an image and/or text and convert it into a digital file, allowing the computer to read and/or display the scanned object

Output Device

Any peripheral that receives and/or displays output from a computer. Below are some examples of different types of output devices commonly found on a computer.

Monitor A monitor is a video display screen. Monitor is also called as Visual Display Unit (VDU) or Video Display Terminal (VDT). CRT (Cathode Ray Tube), LCD (Liquid Crystal Display), LED (Light Emitting Diodes), TFT-LCD (Thin Film Technology LCD) are the different types of displays.
CRT (Cathode Ray Tube) Monitors are built very similarly to older (tube) television sets. They are heavy, bulky, take up a lot of desk space, and emit radiation.	LCD (Liquid Crystal Display) Monitors are thin and flat. They are light, compact, take up very little desk space emit no known radiation.
Printer A printer is an output device responsible for taking computer data and generating a hard copy of that data. Inkjet printers, Laser printers, dot matrix are the different types of the printers.
Projector Take the display of a computer screen and project a large version of it onto a flat surface.
Speakers Connected to a computer’s sound card that outputs sounds generated by the computer.

How does a Computer Work?

            A Computer can perform three basic steps to complete any task: input, processing and output. A task is assigned to a computer in a set of step-by-step instructions, which is known as a program. A computer functions in the following manner:

STEP:1

            The Computer accepts the input. The computer input is whatever entered or fed into a computer system . Some examples of input include the words and symbols in a document, numbers for a calculation, instructions for completing a process and so on.

STEP:2

            The computer processes the data. During this stage, the computer follows the instructions using the data that have been input. Examples of processing include calculations, sorting lists of words or numbers and so on.

STEP:3

            The computer produces output. Computer output is the information that has been produced by a computer. Some examples of Computer output includes reports, documents, graphs and so on.        

Inside a Computer:

Computing machines are complex devices made from numerous electronic devices made from numerous electronic components. Many of these components are small, sensitive, and expensive and operate with other components to provide better performance to the computing machines. Therefore, to ensure better performance and increase in the life of these components, they are placed inside a metal enclosure called the system case or cabinet. The system case is a metal plastic box that houses the main components of the computer. It protects the electronic hardware against the heat, light, temperature etc. Roles of system case are:

Structure: The system case provides rigid structure to the components.

Protection: The system case protects the inside of the system from physical damage and electrical interface.

Cooling: The system case provides a cooling system to the vital components.

Organization and Expandability: The system case is a key to the organization of physical systems. If a system case is poorly designed, up gradation or expansion of a peripheral is limited.

Status Display: The system case contains lights or LEDs that provide varied information pertaining to the working of the system to the user. The system case encloses all the components including the motherboard, processors, memory, power supply, expansion slots, cables, removable drives etc.,

Power Supply(SMPS): Power Supply or switch-mode power supply is a transformer and voltage control device that converts incoming AC to DC and then supplies DC to all the components of the computer.

Motherboard: Motherboard also known as system board, is a large multilayered printed circuit board inside a computer. The motherboard contains CPU, BIOS ROM chip, RAM slots and underlying circuitry the CMOS.

BIOS: The BIOS comprises of startup instructions inside the ROM.

CMOS: The motherboard includes a separate block of memory called the Complementary Metal-oxide silicon chip that consumes very low power. This chip is kept alive by a battery even when the computer’s power is off. The most important data which is kept in the CMOS battery is the system time and date.

Storage Devices: Disk drives are the important components present inside the system case. These drives are used to read and write information to and from the processors. The three common diskdrives located inside a system case are the hard drive, floppy drive and CD-ROM.

Processors: The Processors often called as the CPU is the central component of the computer. It is referred to brain of the Computer responsible for carrying out operations in an efficient and effective manner.