(A) Write a note, how data is stored on a 'Hard Disk'. (B) How an 'Optical Fiber' is constructed? How is it helpful in transmitting the electromagnetic radiations? (C) Write a comprehensive note on 'Balanced Diet'. (D) What is 'Artificial Intelligence'? How is it helpful for humanity?

(A) How data is stored on a hard disk

A hard disk drive (HDD) is a non-volatile storage device that stores data magnetically, so it retains the data without power.

Structure: it has one or more rigid circular platters coated with a magnetic material, mounted on a spindle that spins at high speed, commonly 5,400 or 7,200 rpm. A read/write head on a moving actuator arm floats just above each surface. A controller manages all of these operations.

Writing: computers represent data as binary digits. To store them, the head produces a small magnetic field that sets the magnetic direction of tiny regions on the platter. The pattern of these directions encodes the 0s and 1s.

Reading: as the platter spins, the head senses the magnetised regions and changes them back into electrical signals.

Organisation: the surface is divided into concentric tracks, and each track is divided into sectors, the smallest storage unit, typically 512 bytes or 4 KB. The file system keeps a record of where each file is stored. The contents remain in place until overwritten. Solid-state drives, by contrast, store data electrically in flash memory and have no moving parts.

(B) Optical fibre

Construction: an optical fibre is a thin strand, about as thick as a human hair, made of very pure glass or plastic, with three layers:

Core: the central part that carries the light, having a higher refractive index. Cladding: the surrounding layer of lower refractive index, which keeps light in the core. Protective coating: a polymer buffer that shields the fibre from damage and moisture. Many such fibres are bundled together with strengthening fibres and an outer jacket to form a cable.

How it transmits electromagnetic radiation: light, usually infrared radiation from a laser or LED, enters the core. When it hits the core-cladding boundary at more than the critical angle, it undergoes total internal reflection, so it stays within the core and travels long distances even around gentle bends.

It carries signals with very low loss and huge bandwidth, is immune to electromagnetic interference and is hard to tap. Data is converted into light pulses at one end and back into electrical signals at the other. This is why it forms the backbone of the internet and undersea cables.

(C) Balanced diet

A balanced diet provides all essential nutrients in the right amount and proportion to maintain health, energy and normal growth. It varies with age, sex, activity, pregnancy and illness.

Components

Carbohydrates: the main energy source, from whole grains, rice, potatoes and fruit. Proteins: for growth and repair, from pulses, meat, fish, eggs and dairy. Fats: for concentrated energy and absorbing vitamins A, D, E and K, preferably from unsaturated sources such as vegetable oils and nuts. Vitamins and minerals: for immunity, bones, blood and metabolism, from fruit, vegetables and dairy. Fibre: for digestion, from whole grains, vegetables and fruit. Water: for transport, temperature control and all body processes.

As a broad guide, about 45 to 65% of energy can come from carbohydrates, 10 to 35% from protein and 20 to 35% from fat, while limiting sugar, salt, saturated fat and trans fat.

Benefits: it supports growth and immunity, maintains a healthy weight, and reduces the risk of diabetes, heart disease and some cancers. Imbalance causes malnutrition in both forms: undernutrition, such as stunting and anaemia, which is a serious problem in Pakistan, and overnutrition, leading to obesity.

(D) Artificial intelligence

Artificial intelligence (AI) is the field of computer science concerned with building systems that perform tasks normally requiring human intelligence, such as learning, reasoning, understanding language and recognising images. Modern AI relies largely on machine learning, in which systems learn from data.

How it helps humanity

Health: it supports disease detection from scans, drug discovery and personalised treatment. Education: it enables adaptive tutoring and translation. Agriculture: it helps with crop monitoring and targeted water and fertiliser use. Disaster and climate: it improves weather forecasts and flood warnings, and analyses satellite data. Accessibility: it provides speech recognition and tools for people with disabilities. Productivity and safety: it automates dangerous or repetitive work and helps detect fraud.

These benefits depend on responsible use, since AI also raises concerns about bias, privacy, misinformation and jobs.