ICT Fundamentals: Hardware, Software, Networks & Cyber Safety

Data-transfer units are counted in bits per second and use decimal prefixes: 1 kbps = 1,000 bps, 1 Mbps = 10⁶ bps, 1 Gbps = 10⁹ bps. Because 1 byte = 8 bits, a connection of 8 Mbps moves 1 MB per second (taking MB decimally). Worked example. How long does a 250 MB lecture video take to download on a 20 Mbps line? Convert the file to bits: 250 MB × 8 = 2,000 megabits. Divide by speed: 2,000 Mb ÷ 20 Mbps = 100 seconds ≈ 1 min 40 s. Check by the shortcut: 20 Mbps = 2.5 MB/s, and 250 ÷ 2.5 = 100 s. Second example. A 1.5 GB file on a 100 Mbps link: 1.5 GB = 1,500 MB = 12,000 Mb; 12,000 ÷ 100 = 120 s = 2 minutes. Real downloads take longer because the advertised figure is bandwidth (capacity) while the achieved figure is throughput, reduced by latency, sharing and protocol overhead.

Binary ↔ decimal. Place values in base 2 are 1, 2, 4, 8, 16, 32 … from the right. 10110₂ = 1×16 + 0×8 + 1×4 + 1×2 + 0×1 = 16 + 0 + 4 + 2 + 0 = 22₁₀. Reverse direction, 45₁₀ → binary by repeated division by 2, writing remainders: 45 ÷ 2 = 22 r 1; 22 ÷ 2 = 11 r 0; 11 ÷ 2 = 5 r 1; 5 ÷ 2 = 2 r 1; 2 ÷ 2 = 1 r 0; 1 ÷ 2 = 0 r 1. Read the remainders upwards: 101101₂. Check: 32 + 8 + 4 + 1 = 45 ✓. Octal ↔ decimal. Base 8 uses digits 0–7 with place values 1, 8, 64, 512. 157₈ = 1×64 + 5×8 + 7×1 = 64 + 40 + 7 = 111₁₀. And 100₁₀ → octal: 100 ÷ 8 = 12 r 4; 12 ÷ 8 = 1 r 4; 1 ÷ 8 = 0 r 1 → read upwards 144₈. Check: 64 + 32 + 4 = 100 ✓.

Hexadecimal ↔ decimal. Base 16 uses 0–9 and A = 10, B = 11, C = 12, D = 13, E = 14, F = 15, with place values 1, 16, 256, 4096. 3A7₁₆ = 3×256 + 10×16 + 7×1 = 768 + 160 + 7 = 935₁₀. Reverse, 250₁₀ → hex: 250 ÷ 16 = 15 r 10; 15 ÷ 16 = 0 r 15; remainders upwards are 15, 10 → FA₁₆. Check: 15×16 + 10 = 240 + 10 = 250 ✓. Binary ↔ octal and hex by grouping — no arithmetic needed. Take 110101101₂. For octal, group in threes from the right: 110 | 101 | 101 → 6 | 5 | 5 → 655₈. For hex, group in fours from the right, padding the left with zeros: 0001 | 1010 | 1101 → 1 | A | D → 1AD₁₆. Both equal 256 + 128 + 32 + 8 + 4 + 1 = 429₁₀ — three names for one number. This grouping is exactly why programmers write memory addresses and colour codes (#FF0000) in hex: each hex digit is a tidy four bits.

• System software runs the machine and serves other programs: the operating system, device drivers, utilities (antivirus, disk defragmenter, compression, backup) and language translators — a compiler converts a whole high-level program to machine code before running it (C, C++), an interpreter translates and runs line by line (Python, JavaScript), an assembler converts assembly language. Application software does the user's work: word processors, spreadsheets, browsers, media players, LMS platforms such as Moodle. Firmware is software stored permanently in ROM (BIOS/UEFI). Middleware connects applications to each other or to a database.
• Functions of an operating system: (1) process management — scheduling the CPU among running programs; (2) memory management — allocating RAM and running virtual memory; (3) file management — directories, names, permissions; (4) device management — controlling hardware through drivers and spooling print jobs; (5) security — logins, access control; (6) user interface — CLI (command line) or GUI. Types: batch, multiprogramming, time-sharing/multitasking, multi-user, real-time (aircraft, ATMs — response within a deadline), distributed, embedded, mobile. Examples: Windows, macOS, Linux (kernel by Linus Torvalds, 1991), Android (Google, built on the Linux kernel), iOS, Chrome OS; India's BOSS (Bharat Operating System Solutions, C-DAC).
• Open-source versus proprietary software. Open source publishes its source code and licenses anyone to study, modify and redistribute it (GNU GPL, Apache, MIT licences) — Linux, LibreOffice, Firefox, Apache web server, MySQL, Python, Moodle, VLC. The movement descends from Richard Stallman's GNU project (1983) and the Free Software Foundation (1985); the term "open source" and the Open Source Initiative date from 1998; FOSS = Free and Open Source Software. Proprietary software keeps the code secret and licenses only its use — Microsoft Windows and Office, Adobe Photoshop, Oracle Database. Two half-way cases: freeware is free to use but closed (Adobe Acrobat Reader); shareware is a time- or feature-limited trial. Note that "free" in FOSS means freedom, not price — commercial support for Linux is sold.

• By reach: PAN (a few metres — Bluetooth, about 10 m), LAN (a room, building or campus; Ethernet or Wi-Fi; owned by one organisation; the fastest), MAN (a city — cable TV network, a municipal Wi-Fi), WAN (country to globe; leased lines, satellite, undersea fibre; the internet is the largest WAN). Media: twisted-pair copper (Cat 5e/6 with RJ-45 plugs), coaxial cable, optical fibre (light pulses — highest bandwidth, immune to electrical interference); wireless — radio, microwave, infrared, satellite, Wi-Fi (IEEE 802.11), Bluetooth (802.15), NFC (about 4 cm — contactless payment).
• Topologies (the shape of the wiring): bus — one backbone cable, cheap, a single break stops everything; star — every node to a central hub or switch, the most common LAN layout, a node failure is harmless but a hub failure is fatal; ring — each node to two neighbours, data circulates one way by token passing; mesh — every node linked to every other, most reliable and most expensive, needing n(n − 1) ÷ 2 links (for 6 nodes: 6 × 5 ÷ 2 = 15 cables; for 10 nodes: 10 × 9 ÷ 2 = 45); tree — stars joined to a bus backbone; hybrid — any combination.
• Devices, in order of intelligence: a repeater regenerates a weakening signal; a hub copies every incoming packet to all ports (dumb, Layer 1); a switch reads the MAC address and forwards only to the right port (Layer 2); a bridge joins two LAN segments; a router reads the IP address and forwards packets between different networks, choosing the best path (Layer 3) — the box in your home that joins your LAN to the ISP; a gateway translates between different protocol families; a modem (modulator-demodulator) converts digital signals to analog for a telephone or cable line and back; an access point gives wireless devices a way onto a wired LAN; a NIC (network interface card) is the port in each computer, carrying its unique 48-bit MAC address.

Addressing. An IPv4 address is 32 bits, written as four decimal numbers 0–255 separated by dots (192.168.1.1), giving 2³² ≈ 4.3 billion addresses — exhausted, hence IPv6: 128 bits, written as eight groups of four hexadecimal digits separated by colons (2001:0db8:85a3::8a2e:0370:7334), giving 2¹²⁸ ≈ 3.4 × 10³⁸ addresses. 127.0.0.1 is the loopback (your own machine); 192.168.x.x and 10.x.x.x are private ranges used inside LANs. The MAC address is a 48-bit hardware identity (six hex pairs, 00:1A:2B:3C:4D:5E) fixed in the NIC; the IP address is a logical, changeable location. DNS resolves names to IP addresses through a hierarchy: root → top-level domain (TLD) → second-level domain → subdomain. Generic TLDs: .com, .org, .net, .edu, .gov; country-code TLDs: .in, .uk, .us; India's second-level categories: .ac.in (academic), .gov.in (government), .nic.in (NIC), .edu.in, .co.in, .res.in (research).

URL anatomy — worked example. Take https://www.ugc.gov.in:443/pdfnews/report.pdf?year=2020#page3. Reading left to right: https is the scheme/protocol (the rules for fetching); :// separates it; www is the subdomain (host name); ugc is the second-level domain (the organisation); gov.in is the top-level domain (a government body in India); :443 is the port (443 is the default for HTTPS, 80 for HTTP, so it is normally omitted); /pdfnews/report.pdf is the path to the resource on the server; ?year=2020 is the query string (parameters after "?", joined by "&"); #page3 is the fragment (a position inside the page). The domain name proper is ugc.gov.in, and the hierarchy reads right to left: .in → gov → ugc → www. Everything after the domain is case-sensitive on most servers; the domain itself is not.

The TCP/IP model has four layers — Application, Transport, Internet, Network Access — while the older reference OSI model has seven: Physical, Data Link, Network, Transport, Session, Presentation, Application (mnemonic: "Please Do Not Throw Sausage Pizza Away"). Internet vs intranet vs extranet was covered earlier; two further families matter. Web generations: Web 1.0 (1990s) — static, read-only pages; Web 2.0 (term popularised by Tim O'Reilly, 2004) — read-write, user-generated content, blogs, wikis, social media, tagging; Web 3.0 — the semantic web: machine-readable meaning, AI, personalisation, decentralised/blockchain services. Cloud computing delivers computing as a metered service over the internet in three models: IaaS — raw virtual machines, storage and networks (Amazon EC2, Azure VMs); PaaS — a ready development and hosting platform (Google App Engine, Heroku); SaaS — finished applications used in a browser (Gmail, Google Docs, Office 365, Moodle Cloud). Deployment is public, private, hybrid or community; the Government of India's cloud is MeghRaj (GI Cloud, 2014). Rule of thumb: IaaS rents the building, PaaS rents a furnished office, SaaS rents a desk with the work already set up.

E-mail anatomy. The first networked e-mail was sent by Ray Tomlinson in 1971, who chose the @ sign to separate the local part (user name) from the domain; the domain part is case-insensitive. A message has a header — From, To, CC (carbon copy, visible to all), BCC (blind carbon copy, hidden from all others), Subject, Date, Message-ID — a body, an optional signature block, and attachments, which are carried by MIME (Multipurpose Internet Mail Extensions), the standard that lets a text-only protocol carry images and documents; providers cap attachment size at a few tens of megabytes, so large files go as cloud links. Spam is unsolicited bulk mail, filtered by keyword, sender-reputation and Bayesian filters; Reply answers the sender, Reply All answers everyone in To and CC (never BCC), Forward passes the mail to a new person. A mailing list or listserv distributes one message to many subscribers; a newsgroup is a threaded public discussion board.

• The phishing family is social engineering — attacking the person, not the machine. Phishing: a fraudulent e-mail or fake website imitating a bank, university or portal to harvest passwords, OTPs and card numbers. Spear phishing: aimed at one named person; whaling: aimed at a senior executive. Vishing (voice): the same fraud by phone call — "your KYC has expired". Smishing (SMS): by text message with a shortened link. Pharming: poisoning DNS so that a correctly typed address lands on a fake site. Tell-tales: urgency, a mismatched sender domain, a link whose visible text differs from its real address, requests for OTP or PIN, which no genuine bank ever makes.
• Safeguards. A firewall filters traffic between a trusted network and the internet by rules — packet-filtering (by address and port), stateful (tracks connections), application/proxy (inspects content); it may be hardware or software (Windows Defender Firewall). Encryption turns plaintext into ciphertext: symmetric uses one shared key (AES — fast, key must be exchanged secretly); asymmetric uses a public key to encrypt and a private key to decrypt (RSA — the basis of HTTPS and digital signatures); a hash (SHA-256) is a one-way fingerprint used to check integrity and store passwords. HTTPS/TLS encrypts the browser-to-server channel; end-to-end encryption means even the service provider cannot read the message. A strong password is long (12+ characters), mixes cases, digits and symbols, avoids dictionary words and personal data, is unique per site and ideally a passphrase kept in a password manager. Two-factor authentication (2FA) combines two of the three factors — something you know (password/PIN), something you have (phone OTP, hardware token, smart card), something you are (fingerprint, face, iris); an OTP alone is one factor, password + OTP is two. Add regular updates and patches, antivirus, the 3-2-1 backup rule (three copies, two media, one off-site) and HTTPS-only browsing.

The IT Act, 2000 was enacted on 9 June 2000 on the model of the UNCITRAL Model Law on Electronic Commerce (1996); it gave legal recognition to electronic records and digital signatures, created the Controller of Certifying Authorities (CCA, Sec. 17) and the adjudicating machinery, and amended the IPC, Evidence Act and RBI Act. Digital signature versus electronic signature. A digital signature (Sec. 2(1)(p) and Sec. 3) is one specific technique: the sender's software makes a hash of the document and encrypts it with the sender's private key; the receiver decrypts with the sender's public key and recomputes the hash — a match proves both authenticity (who signed) and integrity (nothing changed). It rests on an asymmetric cryptosystem and a Digital Signature Certificate (DSC) issued by a licensed Certifying Authority. An electronic signature (Sec. 3A, inserted by the 2008 amendment) is the broad category — any reliable technique listed in the Second Schedule, including Aadhaar-based eSign using e-KYC and OTP. So every digital signature is an electronic signature, but not every electronic signature is digital; a scanned image of a handwritten signature is neither, because it proves nothing about integrity.