CCC Notes in English

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CCC Notes in English

CCC Notes in English

MEMORY SYSTEM IN A COMPUTER

There are two kinds of computer memory: primary and secondary. Primary memory is accessible directly by the processing unit. RAM is an example of primary memory You can store and retrieve data much faster with primary memory compared to secondary memory. Secondary memory such as Floppy disks, Magnetic disk, CD, etc., is located outside the computer.

1.  Random Access Memory (RAM): The primary storage is referred to as random access memory (RAM) because it is possible to randomly select and use any location of the memory directly store and retrieve data. Each of RAM’s locations stores one byte of information. As soon as the computer is switched off the contents of the primary memory is lost. So now we can say that RAM is volatile memory.

Computer Memory

Fig. : RAM

2.  Read Only Memory (ROM): There is another memory in computer, which is called Read Only Memory (ROM). Again it is the ICs inside the PC that form the 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 personal computer. The ROM can only be read by the CPU but it cannot be changed.

The basic input/output (BIOS) program is stored in the ROM that examines and initializes various equipment attached to the PC when the switch is made ON. The memories, which do not loose their content on failure of power supply, are known as non-volatile memories. ROM is non-volatile memory.

3.   PROM There is another type of primary memory in computer, which is called Programmable Read Only Memory (PROM).

4.  EPROM: This stands for Erasable Programmable Read Only Memory, which over come the problem of PROM & ROM.

5.   Cache Memory: The speed of CPU is extremely high compared to the access time of main memory. Therefore the performance of CPU decreases due to the slow speed of main memory. To decrease the mismatch in operating speed, a small memory chip is attached between CPU and Main memory whose access time is very close to the
processing speed of CPU. It is called CACHE memory.

SECONDARY STORAGE

1. Hard Disk Drive: The hard drive is the data center of the computer. This is where the software is installed, and it’s also where your documents and other files are stored. The hard drive is long-term storage, which means the data is still saved even if you turn the computer off or unplug it.

When you run a program or open a file, the computer copies some of the data from the hard drive onto the RAM so that it can access the data more easily. When you save a file, the data is copied back to the hard drive. The faster the hard drive is, the faster your computer can start up and load programs.

Hard Disk Drive

Fig. : Hard Disk Drive

2. Magnetic Tape: Magnetic tapes are used for large computers like mainframe computers where large volume of data is stored for a longer time. In PC also you can use tapes in the form of cassettes.

Magnetic Tape

Fig. : Magnetic Tape

3. Floppy Disk: It is similar to magnetic disk. They are 5.25 inch or 3.5 inch in diameter. The capacity of a 5.25-inch floppy is 1.2 mega bytes whereas for 3.5 inch floppy it is 1.44 mega bytes.

Floppy Disk

Fig. : Floppy Disk

4. Optical Disk: Compact Disk/ Read Only Memory (CD-ROM): CD-ROM disks are made of reflective metals. CD-ROM is written during the process of manufacturing by high power laser beam. Here the storage density is very high, storage cost is very low and access time is relatively fast. 

Each disk is approximately 4 1/2 inches in diameter and can hold over 600 MB of data. As the CD-ROM can be read only we cannot write or make changes into the data contained in it.

Unit of Computer Memory:

Bit is the smallest unit of data storage in computers

                        1 Bit                =          1 Character

                        1 Nibble          =          4 Bits

                        1 Byte             =          8 Bits

                        1 Kilo Byte     =          1024 Byte

                        1 Mega Byte   =          1024 Kilo Byte (KB)

                        1 Giga Byte     =          1024 Mega Byte (MB)

INPUT DEVICES

1. Keyboard: – This is the standard input device attached to all computers. The layout of keyboard is just like the traditional typewriter.

Keyboard

Fig. : Key Board

2. Mouse: – Mouse is an input device shown in Fig. 2.8 that is used with your personal computer. It rolls on a small ball and has two or three buttons on the top. When you roll the mouse across a flat surface the screen censors the mouse in the direction of mouse movement.

Mouse

Fig. : Mouse

3. Scanner: If we want to input a picture the keyboard cannot do that. Scanner is an optical device that can input any graphical matter and display it back. The common optical scanner devices are Magnetic Ink Character Recognition (MICR), Optical Mark Reader (OMR) and Optical Character Reader (OCR).

Scanner

 Fig. : Scanner

Magnetic Ink Character Recognition (MICR): – This is widely used by banks to process large volumes of cheques and drafts. Cheques are put inside the MICR. As they enter the reading unit the cheques pass through the magnetic field which causes the read head to recognise the character of the cheques.

Optical Mark Reader (OMR): This technique is used when students have appeared in objective type tests and they had to mark their answer by darkening a square or circular space by pencil. These answer sheets are directly fed to a computer for grading where OMR is used.

Optical Character Recognition (OCR): – This technique unites the direct reading of any printed character.
Suppose you have a set of hand written characters on a piece of paper. You put it inside the scanner of the computer. This pattern is compared with a site of patterns stored inside the computer. Whichever pattern is matched is called a
character read. Patterns that cannot be identified are rejected. OCRs are expensive though better the MICR.

OUTPUT DEVICES

1. Visual Display Unit: The most popular input/output device is the Visual Display Unit (VDU). It is also called the monitor.

2. Terminals: It is a very popular interactive input-output unit. It can be divided into two types: hard copy terminals and soft copy terminals. A hard copy terminal provides a printout on paper whereas soft copy terminals provide visual copy on monitor.

3. Printer: It is an important output device which can be used to get a printed copy of the processed text or result on paper.

Types of Printer: There are different types of printers that are designed for different types of applications. Depending on their speed and approach of printing, printers are classified as impact and non-impact printers.

1. Impact Printer: Impact printers use the familiar typewriter approach of hammering a typeface against the paper and inked ribbon. Dot-matrix printers are of this type.

2. Non- Impact Printer: Non-impact printers do not hit or impact a ribbon to print. They use electro-static
chemicals and ink-jet technologies. Laser printers and Ink-jet printers are of this type.

Printer

                                                                                        Fig. :  Printer

Also Read: CCC Study material in English, Computer Basic Knowledge

 

HARDWARE/SOFTWARE

WHAT IS HARDWARE?

Hardware are those parts of computer to which we can see, fell as well as touch. These parts of computer are called hardware. For example Monitor, Keyboard, mouse, CD/DVD etc.

Computer Hardware

Fig. :  HARDWARE

WHAT IS SOFTWARE?

As you know computer cannot do anything without instructions from the user. In order to do any specific job you have to give a sequence of instructions to the computer. This set of instructions is called a computer program. Software refers to the set of computer programs.

Computer Software

Fig. : Software

TYPES OF SOFTWARE

Computer software is normally classified into two broad categories.

• Application Software
• System software

1. Application Software: Application Software is a set of programs to carry out operations for a specific application. These software help the user to perform day to day task.