Chapter 3 Computer Hard ware Mathematics Department

A computer performs basically five major operations : it accepts data or instructions by any way of input, it stores data, it can process data as required by the user, it gives results in the form of output, and it controls all operations inside a computer Mathematics Department

Computer Hardware Refers to the physical components Not one device but a system of many devices Major types of components include: Central Processing Unit Main memory Secondary storage devices Input devices Output devices

Organization of a Computer System Central Processing Unit Input Device Output Device Main Memory Secondary Storage

The CPU Fetches instructions from main memory Carries out the operations commanded by the instructions Each instruction produces some outcome A program is an entire sequence of instructions Instructions are stored as binary numbers Binary number - a sequence of 1’s and 0’s

Main Memory Commonly known as random access memory, or just RAM Holds instructions and data needed for programs that are currently running RAM is usually a volatile type of memory Contents of RAM are lost when power is turned off

Secondary Storage A nonvolatile storage medium Contents retained while power is off Hard disk drives are most common Records data magnetically on a circular disk Provides fast access to large amounts of data Optical devices store data on CD’s as pits USB flash memory devices High capacity device plugs into USB port Portable, reliable, and fits easily in a pocket

Input Devices Any type of device that provides data to a computer from the outside world For example: Keyboard Mouse Scanner

Output Devices Any type of device that provides data from a computer to the outside world Examples of output data: A printed report An image such as a picture A sound Common output devices include: Monitor (display screen) Printer

CPU Components Two typical components of a CPU are: The arithmetic logic unit (ALU), which performs arithmetic and logical operations. The control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary. Mathematics Department

ALU The actual processing of the data and instruction are performed by Arithmetic Logical Unit The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison. Data is transferred to ALU from storage unit when required Mathematics Department

Control Unit (CU) The Control Unit acts like the supervisor It extracts instructions from memory and decodes and executes them, and sends the necessary signals to the ALU to perform the operation needed. The control unit determines the sequence in which computer programs and instructions are executed. Processing of programs stored in the main memory, interpretation of the instructions and issuing of signals for other units of the computer to execute them. Mathematics Department

MEMORY There are two kinds of computer memory: primary and secondary. Primary memory is accessible directly by the processing unit. RAM (Random access memory) is an example of primary memory As soon as the computer is switched off the contents of RAM is lost. You can store and retrieve data much faster with primary memory compared to secondary memory Mathematics Department

Primary memory is more expensive than secondary memory. Secondary memory such as floppy disks ,hard magnetic disk, etc., is located inside and outside the computer. Primary memory is more expensive than secondary memory. The size of primary memory is less than that of secondary memory. Primary memory is faster than secondary memory. Mathematics Department

Read Only Memory (ROM) There is another memory in computer, which is called Read Only Memory (ROM). The storage of program and data in the ROM is permanent. The ROM stores some standard processing programs supplied by the manufacturers to operate the computer. The ROM can only be read by the CPU but it cannot be changed. Mathematics Department

PROM is another type of primary memory in computer, which is called Programmable Read Only Memory (PROM). You know that it is not possible to modify or erase programs stored in ROM, but it is possible for you to store your program in PROM chip. Once the programmes are written it cannot be changed and remain intact even if power is switched off. Programs or instructions written in PROM or ROM cannot be erased or changed. Mathematics Department

When the EPROM is in use information can only be read. EPROM: Erasable Programmable Read Only Memory, which over come the problem of PROM & ROM. EPROM chip can be programmed time and again by erasing the information stored earlier in it. When the EPROM is in use information can only be read. Mathematics Department