4 bits (b) = 1 nibble

8 bits (b) = 1 byte (B)

1024 bytes (B) = 1 kilobyte (KB)

1024 kilobyte (KB) = 1 megabyte (MB)

1024 megabyte (MB) = 1 gigabyte (GB)

1024 gigabyte (GB) = 1 terabyte (TB)

1024 terabyte (TB) = 1 petabyte (PB)

1024 petabyte (PB) = 1 exabyte (EB)

1024 exabyte (EB) = 1 zettabyte (ZB)

1024 zettabyte (ZB) = 1 yottabyte (YB)

• Cache-
  

  Advantages
  1. Faster than main memory
  2. Consumes less access time than main memory
  3. Stores the program that can be executed within a short period of time
  4. Stores data for temporary use

  Disadvantages
  1. Limited capacity
  2. Very expensive

• Primary Memory (Main Memory)-
  

  It is a volatile memory with low capacity, in which data can be lost, when power is switched off.
  Characteristics:
  1. These are semiconductor memories
  2. It is also known as Main Memory
  3. Usually volatile memory
  4. Data is lost when data is switched off
  5. It is the working memory of the computer
  6. Faster than secondary memory
  7. Computer cannot run without primary memory

• Secondary Memory (External Memory)-
  

  It is a non-volatile memory, where data remains, even after the power is switched off.
  Characteristics:
  1. These are magnetic & optical memories
  2. It is also known as Backup Memory
  3. It is a non-volatile memory
  4. Data is permanently stored even after power is switched off
  5. It is used for storage of data in computer
  7. Computer may run without secondary memory
  8. Slower than primary memory

Non-Impact Printers:

• Leaser Printer-
  

  Advantages
  1. Very high speed
  2. Very high quality output
  3. Good graphics quality
  4. Supports more fonts & different character size

  Disadvantages
  1. Expensive
  2. Cannot be used to produce multiple copies of a document ina single printing

• Inkjet Wheel-
  

  Advantages
  1. High quality printing
  2. More reliable

  Disadvantages
  1. Expensive as the cost per page is high
  2. Slow as compared to laser printer

• Monitors:
  

There are 2 kinds of screen used in monitor:
1. Cathode Ray Tube (CRT):
     Disadvantages:
a. High power consumption
b. Large in size
2. Flat Panel Display:
      2 kinds:
      1. Emissive Display:
           Converts electrical energy into light. Example: LED (Light Emitting Diodes)
      2. Non-Emissive Display:
           Converts light from some other sources into graphics pattern. Example: LCD (Liquid Crystal Device)

• Printers

• Keyboard

• Mouse

• Joy Stick

• Light pen:
  

  It is used to select a displayed menu item or draw pictures on monitor.

• Track Ball:
  

  It is used in laptop or notebook in place of a mouse.

• Scanner

• Digitizer:
  

  It is also known as tablet or graphics tablet, which can convert graphics & pictorial data into binary inputs.

• Microphone

• Magnetic Ink Card Reader (MICR):
  

  It is generally used in banks as there are large number of cheques to be processed every day. The bank’s code number and cheque number are printed on the cheques with a special type of ink that contains particles of magnetic material that are machine readable.

• Optical Character Reader (OCR):
  

  It is used to scan text optically, character by character, converting them into machine readable code, and stores the text in the system memory.

• Bar Code Reader

• Optical Mark Reader (OMR):
  

  It is especially used for checking answer sheets in examinations, having multiple choice questions.

Output Unit

It consists of devices, which help us to get information from the computer.

CPU

Central Processing Unit. It is the brain of the computer, which performs all kinds of processing operations. It consists of:

• Arithmetic & Logic Unit (ALU):
  It consists of arithmetic & logic section
  Arithmetic section performs all kinds of arithmetic operations, like addition, subtraction, multiplication, division and other complicated arithmetic operations.
  Logic section performs all kinds of logical operations, like comparison, selection merging of data and others.

• Memory Unit (MU):
  Also called storage unit. It does the following work:

1. It stores all the data and the instructions required for processing.
2. It stores intermediate results of processing.
3. It stores the final results of processing before these results are released to an output device.
4. All inputs and outputs are transmitted through the main memory.

• Control Unit (CU):
  It controls the operations of all parts of the computer. Its function includes:

1. It is responsible for controlling the transfer of data and instructions among other units of a computer.
2. It manages and coordinates all the units of the computer.
3. It obtains the instructions from the memory, interprets them, and directs the operation of the computer.
4. It communicates with input/output devices for transfer of data or results from storage.
5. It does not store data.

Programming Language

It is a kind of language, which consists of a set of instruction to provide a particular result as output. Categories:

1. Machine Language:
   Also known as machine code or object code. It is coded in the form of binary and hexadecimal numbers, which a computer can understand.
2. Assembly Language:
   Also known as assembly code. It is a low-level language, which is often used by microprocessors and consists of symbolic representation of machine code.
3. High Level Language:
   Also known as HLL. These are user friendly programming languages, like C, C++, JAVA, which are generally used by human operators or programmers to solve a given problem. They require compiling/interpreting.
4. System Language:
   These languages are designed for writing system software, which requires a different approach when compared with application software.
5. Scripting Language:
   These are HLL, which do not require any kind of compiling, like JavaScript.

Evolution Of Internet

It started from the year 1969, when the concept of internet was originated.

• The origin of Internet devised from the concept of Advanced Research Project Agency Network (ARPANET).
• ARPANET was developed by United States Department of Defence.
• Basic purpose of ARPANET was to provide communication among the various bodies of government.
• Initially, there were only four nodes, formally called Hosts.
• In 1972, the ARPANET spread over the globe with 23 nodes located at different countries and thus became known as Internet.  
• By the time, with invention of new technologies such as TCP/IP protocols, DNS, WWW, browsers, scripting languages, Internet provided a medium to publish and access information over the web.

Advantages

• Online communication with other people from any location.
• Search for any kind of information.
• It also serves as a medium of entertainment
• It allows us to use many services like:
  1.  Internet banking
  2.  Online shopping
  3.  Matrimonial services
  4.  Online ticket booking
  5.  Data sharing
  6.  Email

Disadvantages

• Chances of disclosure of personal information.
• Spamming, which corresponds to unwanted information in bulk.
• Virus attack.
• Misconception to many people due to certain unauthenticated information.

Hardware

Physical components of a computer, which can be touched & seen.

1. Input Device: Keyboard and mouse
2. Output Device: Monitor and printer
3. Secondary Storage Device: Hard disk, CD and DVD
4. Internal Storage Device: CPU, motherboard and RAM

Hardware & Software Relationship

• Hardware and software are mutually dependent on each other. Both of them must work together to make a computer produce a useful output.
• Software cannot be utilized without supporting hardware.
• Hardware without a set of programs to operate upon cannot be utilized and is useless.
• To get a particular job done on the computer, relevant software should be loaded into the hardware.
• Hardware is a one-time expense.
• Software development is very expensive and is a continuing expense.
• Different software applications can be loaded on a hardware to run different jobs.
• A software acts as an interface between the user and the hardware.
• If the hardware is the ‘heart’ of a computer system, then the software is its ‘soul’. Both are complementary to each other.