Information Technology

BLOCK DIAGRAM OF COMPUTER: http://www.slideshare.net/Qsrealm/block-diagram-of-a-computer

IO DEVICES:  http://www.slideshare.net/Qsrealm/io-devices

OUTPUT DEVICES:  http://www.slideshare.net/Qsrealm/output-devices-14119854

Block Diagram of Computer

Block diagram of a computer

•  INPUT UNIT
• • Computer receives data and instructions through the Input Unit.
• • The input unit consists of one or more input devices.
• • Input devices include: 
• Keyboard
• Mouse
•  Joystick
•  Scanner
•  FUNCTIONS OF INPUT UNIT
• • Accept the data and instructions from the outside world.
• • Convert it to a form that the computer can understand.
• • Supply the converted data to the computer system for further processing.
•  OUTPUT UNIT
• • Computer provides information and results of computation to the outside world through the Output Unit.
• • The output unit consists of one or more output devices.
• • Output devices include:
• Monitor
• Printer
•  FUNCTIONS OF OUTPUT UNIT
• • Accept the results produced by the computer. (These are in a coded form.)
• • Convert it to a form that the outside world can understand. (OR, Converts it into human readable form.)
• • Supply the converted results to the outside world.
•  CENTRAL PROCESSING UNIT CPU
• • It is the brain of the computer.
• • The ALU and the Control Unit (CU) of a computer system are jointly known as the central processing unit.
• • CPU performs actual processing of data, according to instructions from programs.
•  3 MAIN PARTS OF CPU
• • CONTROL UNIT (CU)
• • ARITHMETIC LOGIC UNIT (ALU)
• • REGISTERS• ( Registers are small high speed storage areas. )
•  FUNCTIONS OF CPU
• • It performs all calculations.
• • It takes all decisions.
• • It controls all units of the computer.
•  CONTROL UNIT
• • It controls all other units in the computer.
• • It is the central nervous system of the computer that controls and synchronizes its working.
•  FUNCTIONS OF CONTROL UNIT
• • It instructs the input unit, where to store the data after receiving it from the user.
• • It controls the flow of data and instructions from the storage unit to ALU.
• • It also controls the flow of results from the ALU to the storage unit.
• • The control unit determines the sequence in which computer programs and instructions are executed.
• • The control unit is also capable of shutting down the computer when the power supply detects abnormal conditions.
•  ARITHMETIC LOGIC UNIT
• • All calculations are performed in the Arithmetic Logic Unit (ALU) of the computer.
• • Whenever calculations are required, the control unit transfers the data from memory to ALU. Once the computations are done, the results are transferred to the memory by the control unit and then it is send to the output unit for displaying results.
•  FUNCTIONS OF ALU
• • It performs all arithmetic operations (addition, subtraction, multiplication, and division).
• • It performs all logic operations (Logic operations test various conditions encountered during processing and allow for different actions to be taken based on the results. )
• • It does comparison and takes decision.
•  STORAGE UNIT
• • The storage unit of the computer holds data and instructions that are entered through the input unit, before they are processed.
•  • Storage devices are divided into two categories: – 
• Primary memory or Main memory
• Secondary memory
•  FUNCTIONS OF STORAGE UNIT
• • It received the data and instructions required for processing from the input unit.
• • It stores the intermediate results.
• • It stores the final results before these results are released to the output unit.
• • It saves data for later use.  

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DIFFERENCES BETWEEN PRIMARY AND SECONDARY MEMORIES

Primary Memory	Secondary Memory
These are semiconductor memories.	These are magnetic and optical memories.
They are characterized as volatile random access memories (RAM) or non-volatile memories (ROM).	They are non-volatile.
They contain program and data that is currently being used by micro processor.	These are used to for bulk storage.
These memories are fast enough to interact with the microprocessor.	Slower than primary memories.
These are costlier as compared to secondary memory.	These are cheaper comparatively.
Also known as Main Memory	Also known as Backup Memory or Auxiliary Memory.
It is implemented by RAM and ROM.	E.g. Tapes, Floppies, Hard Discs, CD ROMs, DVDs

 
Differences Between Compiler and Interpreter:

COMPILER	INTERPRETER
It converts all the program into machine code at a time.	It converts the program line by line into machine code.
Debugging is slow because it removes errors of whole program at a time.	Debugging if fast because it removes errors line by line.
It takes less time to convert the whole program into machine code.	It takes more time to convert the whole program in machine code.
It converts the program only after all types of errors are removed from the program.	Every time error is found, it checks the whole program again line by line.
It produces the object code after compilation.	No object code is produced.
Program execution is fast.	Program execution is relatively slow.