Alisha Mahajan is teaching live on Unacademy Plus
1. Anatomy of a Digital Computer 1.1 Introduction We should keep in mind that a computer is a programmable machine. The two main characteristics of a computer are (i) it responds to a specific set of instructions in a well- defined manner. (ii) It can execute a pre-recorded list of instructions (a program). Modern computers are electronic and digital. The actual machinery - wires, transistors and circuits is called hardware; the instructions and data are called software.
All general purpose computers require the following hardware components: (i) Central Processing Unit (CPU): The 'brain' of the computer, the component that actually executes instructions. (ii) Memory : It enables a computer to store, at least temporarily, data and programs. (ii) Input device : Usually a keyboard or mouse is used to read data and programs into the computer.
(iv) Output device: A display screen, printer, etc. that lets you see what the computer has accomplished (v) Mass storage device: It allows a computer to permanently store large amounts of data. Common mass storage devices include disk drive and tape drive. In addition to these components, many others make it possible for the basic components of a computer to worlk together efficiently
1.2 Objectives After going through this lesson, you will be in a position to: identify the basic components of a computer and their working .explain the importance of various units of a computer learn how these units work together to accomplish a given job
1.3 Functions and Components of a Computer To function properly, the computer needs both hardware and software. Hardware consists of the mechanical and electronic devices, which we can see and touch. The software consists of programs, the operating system and the data that reside in the memory and storage devices. A computer does mainly the following four functions: Receive input -Accept data/information from outside through various input devices like the keyboard, mouse, scanner, etc. Process information-Perform arithmetic or logical operations on data/information.
. Produce output-Communicate information to the outside world through output devices like monitor, printer, etc. .Store information-Store the information in storage devices like hard disk, floppy disks, CD, etc These four basic functions are responsible for everything that computers do. The hardware components of the computer specialize in any one of these functions.
Computer hardware falls into two categories: processing hardware and the peripheral devices. The Processing hardware consists of the Central Processing Unit (CPU), and as its name implies, is where the data processing is done. Peripheral devices allow people to interact with the CPU. Together, they make it possible to use the computer for a variety of task
Central Processing Unit (CPU) This part of the computer that executes program instructions is known as the processor or Central Processing Unit (CPU). In a microcomputer, the CPU is based on a single electronic component, the microprocessor chip, within the system unit or system cabinet. The system unit also includes circuit boards, memory chips, ports and other components. A microcomputer's system cabinet will also house disk drives, hard disks, etc., but these are considered separate from the CPU. The CPU has two parts -The Control Unit (CU) and the Arithmetic Logic Unit (ALU). In a microcomputer, both are on a single microprocessor chip
Arithmetic Logic Unit (ALU) Arithmetic Logic Unit, usually called the ALU, performs two types of operations arithmetical and logical. Arithmetical operations are the fundamental mathematical operations consisting of addition, subtraction, multiplication and division. Logical operations consist of comparisons. That is two pieces of data are compared to see whether one is equal to, less than, or greater than the other.
Memory Memory - also known as the primary storage or main memory - is a part of the Micro computer that holds data and instructions. Part of the contents of the memory is held only temporarily, that is, it is stored only as long as the micro computer is turned on. When you turn the machine off, the contents are lost. The capacity of the memory to hold data and program instructions varies in different computers. The original IBM PC could hold approximately several thousand characters of data or instructions only. But modern microcomputers can hold millions or even billions of characters in their memory.
Registers Computers also have several additional storage locations called registers. These appear in the Control Unit and ALU and make processing more efficient. Registers are a sort of special hi-speed storage areas that hold data and instructions temporarily during processing. They are parts of the Control Unit and ALU rather than the memory. Their contents can, therefore be handled much faster than the contents of the memory.
Addresses To locate the characters of data or instructions in the main memory, the computer stores them in locations known as addresses. A unique number designates each address. Addresses can be compared to post office mailboxes. Their numbers remain the same, but contents continuously change.
4. The control unit recognizes this signal and routes the signal to an address in memory - say address 7. 5. After completing the above instruction, the next instruction tells the user, "Enter 2nd Number." 6. The user types the number 4 on the keyboard. An electronic signal is sent to the CPU 7. The control unit recognizes this signal and routes it to memory address 8. 8. The next program instruction is executed - "Multiply 1st and 2nd Numbers."
1.4.1 Key board The keyboard is very much like a standard typewriter keyboard with a few additional keys. The basic QWERTY layout of characters is maintained to make it easy for the trained typist to use the system. The additional keys are included to perform certain special functions such as loading a program, edition a text, etc. These are knowrn as function keys that vary in number from system to system.
1.4.5 Bar Code Reader These devices are generally available in super markets, bookshops, etc. Bar-code readers are photoelectric scanners that read the bar codes or vertical zebra striped marks, printed on product containers. Supermarkets use a bar code system called the Universal Product Code (UPC). The bar code identifies the product to the supermarket's computer which has a description and the latest price of the product. The computer automatically tells the Point of Sales (POS) terminal what the price is.
1.4.6 Digitiging Tablet This is an input device that enables you to enter drawings and sketches into a computer. A digitiging tablet consists of an electronic tablet and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons. A pen (also called a stylus) looks like a simple ballpoint pen but uses an electronic head instead of ink. Thee tablet contains electronic field that enables it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer. Digitiging tables are also called digitizers, graphics tables, touch tables or simply tables.
1.4.7 Scanner Scanner is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use. A scanner works by digitizing an image dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen and manipulated by programs. Optical scanners do not distinguish text from illustrations, they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages.
1.4.9 Light Pen Light pen is an input device that utilizes a light-sensitive detector to select objects on a display screen. 1.4.10 Speech input devices Speech or voice input devices convert a person's speech into digital form. These input devices, when combined with appropriate software, form voice recognition systems. These systems enable users to operate microcomputers using voice commands.
Intext Questions 1.1 1. What are the four basic functions performed by the computer?
Explain 2. What is a scanner briefly.
3. Choose the correct answer: (a) The task of performing arithmetic and logical operations is performed by. (i) ALU (ii) Editor (ii) storage (iv) output
(c) The process of producing results from the data for getting useful information is called (i) output (ii) input (iii) processing (iv) storage