Notes By Tanuja Banerjee, Computer teacher St. Anne’s Girls” High School
This chapter in Computer Class 7 Computer Hardware deals with the physical components called Hardware–The students will have a fair idea of the basic physical components that make the computer, uses of the components and their nomenclature.
Computer is derived from the word ‘Compute’ which means to calculate.
Computer Hardware– All physical parts of the computer that form the computer system are called computer hardware. Hardware can be touched and felt or in other words hardware devices are tangible.
Hardware components of computer system are-
- Input Devices
- Output Devices
- Processing unit
Input Device
The device through which we enter raw data in computer is called Input Device. Example- Keyboard, Mouse, Light pen, Joystick, microphone, Webcam, Scanners etc.
Sir Christopher Latham Sholes is regarded as inventor of QWERTY Keyboard layout.
Dr.Engelbart is the inventor of computer mouse.
Output Device
Output devices are used to display the data that we input into a computer and the results, which we get after processing. Examples- Monitors, Printers, Plotters, 3D printers, Speakers, Headphones, Braille display, Speech Generating Device (SGD), Projectors etc.
Processing Unit
CPU is a part of computer system , which basically does everything. It stores , manipulates and executes the instructions. That is why CPU is also called Brain of Computer.
CPU has three parts-
- Control Unit
- Arithmetic Logical Unit
- Memory Unit
Control Unit
CU controls the flow of data. It receives the instructions, decodes them and passes them to the ALU for execution. If required it passes the data to Memory Unit for storage. As it co-ordinates all the functions, it is considered as Central Nervous System.
Arithmetic Logical Unit-
It performs arithmetic and logical operation.
Memory Unit-
It is the store house of computer. Data and instructions are placed here before being executed and the results are also stored after execution. Memory is of two types-
- Internal Memory / Primary Memory/ Main Memory
- External Memory
Internal Memory-
It is also called Primary Memory or Main memory. It is the built in memory to store data and instructions while the computer is working. The data stored in internal memory is erased when the computer is turned off. Control Unit can access it directly.
Primary memory is of two types-
- RAM– Full form of RAM is Random Access Memory. Whatever information we enter into the computer that exists in RAM. Control Unit accesses the RAM randomly and not sequentially from the first memory location. This makes storage and retrieval very fast. RAM is volatile in nature. Data gets erased when power is switched off. We can read write both from RAM.
- ROM– Full form of ROM is Read Only Memory. We can read only from ROM but can’t write. It is non-volatile memory as it stores information permanently which cannot be altered. The primary use of ROM is during the booting procedure.
External Memory-
Primary memory is fast but expensive and volatile. So another type of cheap memory was developed that could store large amount of data. It is also called auxiliary memory where data can be stored permanently for future use.
Common storage devices-
- Floppy Disk- It is a small magnetic disk covered with a plastic casing. They can store small amounts of data. Another name of floppy disk is diskette. Because of low storage capacity, it is not in use now.
- CD- Full form of CD is Compact Disk. These are circular disks that use optical rays, usually lasers, to read and write data. Its storage space is about 700 MB. They are portable and cheap.
- DVD- DVD stands for Digital Versatile Disk. It is also circular shaped. The storage capacity of DVD varies from 4.1 GB to 17 GB of data.
- Flash Drive- It is a small lightweight, removable and rewritable flash memory data storage device. It is also called Pen drive, Thumb drive or USB drive. It was first invented in 1998 by Dov Moran.
- Hard Disk Drive- The hard disk drive is a high capacity storage device that uses magnetic disks to store data. It is usually connected inside the CPU.
- Blue-ray Disk- It is an optical storage media used to store high definition video and other multimedia files. BD uses shorter wavelength blue- violet laser to read and write data. BDs can store upto 128 GB data.
Difference between Primary and Secondary Memory-
S.N |
Primary Memory |
Secondary Memory |
| 1. | It is volatile | It is non- volatile |
| 2. | It is not portable | It is portable |
| 3. | Smaller storage capacity | Larger storage capacity |
| 4. | Example- RAM | Example- Pen drive, CD, DVD, Hard disk etc. |
Difference between RAM and ROM-
S.N |
RAM |
ROM |
| 1. | Full form of RAM is Random Access Memory | Full form of ROM is Read Only Memory |
| 2. | RAM is temporary or volatile in nature | ROM is permanent in nature |
| 3. | We can read- write both from RAM | We can read only but can’t write in ROM |
