Computer Knowledge — Tier-II Module Essentials

Hardware is every physical part you can touch; software is the set of instructions. The classic exam question simply asks you to sort a list of devices into input, output or both. Learn these three buckets and you will never lose that mark.

• Input devices: keyboard, mouse, joystick, trackball, light pen, scanner, webcam, microphone, graphics tablet, and the four readers — OMR (Optical Mark Reader, used for objective answer sheets), OCR (Optical Character Reader, converts printed text to editable text), MICR (Magnetic Ink Character Reader, used on bank cheques) and barcode/QR reader. A biometric fingerprint sensor is also input.
• Output devices: monitor (also called VDU), printer, plotter (large engineering drawings), speaker, headphone, projector. Printers split into impact (dot-matrix, line printer — noisy, can make carbon copies) and non-impact (inkjet, laser, thermal — quieter, sharper). DPI measures print resolution.
• Both input and output: touch screen, modem, network interface card, hard disk and pen drive (they accept and return data), multi-function printer with a built-in scanner, headset with microphone.
• Common ports: USB (universal, hot-swappable), HDMI (digital audio + video), VGA (older analog display), RJ-45 (wired Ethernet), 3.5 mm audio jack, PS/2 (legacy keyboard and mouse). A port is a socket; a bus is the internal pathway that carries data, addresses and control signals.

Memory divides into primary (main) memory, which the CPU can address directly, and secondary (auxiliary) memory, which stores data permanently but must be loaded into primary memory before use. Primary memory is fast, small and expensive per byte; secondary memory is slow, large and cheap. The full speed ladder, fastest first, is: registers → cache → RAM → SSD/hard disk → optical disc → magnetic tape.

On secondary storage capacities, remember the standard figures: a CD holds about 700 MB, a single-layer DVD about 4.7 GB, and a single-layer Blu-ray about 25 GB. A hard disk drive (HDD) stores data magnetically on rotating platters with read/write heads; a solid state drive (SSD) uses flash memory with no moving parts, so it is faster and shock-resistant. Magnetic tape allows only sequential access and survives mainly for archival backup.

A computer stores everything as bits (binary digits, 0 or 1). Four bits make a nibble, eight bits make a byte, and one byte holds exactly one character in ASCII. Because addressing is binary, every step up the unit ladder multiplies by 1024 = 2¹⁰, not by 1000 — that single fact is the most frequently tested line in the whole module.

Four number systems appear in the syllabus: binary (base 2, digits 0–1), octal (base 8, digits 0–7), decimal (base 10) and hexadecimal (base 16, digits 0–9 then A=10, B=11, C=12, D=13, E=14, F=15). To go from any base to decimal, multiply each digit by the base raised to its place value and add. To go from decimal to any base, divide repeatedly by the base and read the remainders bottom to top.

1. Binary to decimal. (1101)₂ = 1×8 + 1×4 + 0×2 + 1×1 = 13. Similarly (10110)₂ = 16 + 0 + 4 + 2 + 0 = 22.
2. Decimal to binary. For 25: 25÷2 leaves 1, 12÷2 leaves 0, 6÷2 leaves 0, 3÷2 leaves 1, 1÷2 leaves 1. Reading upwards, 25 = (11001)₂, and the check is 16 + 8 + 1 = 25. For 60 the same method gives (111100)₂, since 32 + 16 + 8 + 4 = 60.
3. Hexadecimal to decimal. (2F)₁₆ = 2×16 + 15 = 47. And (3C)₁₆ = 3×16 + 12 = 60, which matches the binary answer above.
4. Octal to decimal. (57)₈ = 5×8 + 7 = 47 — the same value as (2F)₁₆, a neat reminder that the number is one thing and its representation another.
5. Binary to hexadecimal, the fast way. Group the bits into nibbles of four from the right and convert each nibble separately: (10101100)₂ = 1010 | 1100 = A | C = (AC)₁₆. Verify in decimal: 128 + 32 + 8 + 4 = 172, and 10×16 + 12 = 172. ✔
6. A landmark pair worth memorising. (255)₁₀ = (FF)₁₆ = (11111111)₂, because eight bits can hold 2⁸ = 256 values, that is 0 to 255. This is why one byte of extended ASCII covers 256 characters.

• System software runs the machine itself: the operating system, device drivers, utility programs and language translators. It is the layer the user rarely opens deliberately.
• Application software does the user work. General purpose packages serve everyone — word processor, spreadsheet, presentation, browser, media player. Specific purpose or customised packages serve one job — railway reservation, payroll, hospital management, school ERP.
• Firmware sits in between: software permanently written into hardware, such as the BIOS stored in ROM that runs the POST (Power-On Self Test) and then loads the operating system.
• Utility software maintains the system: antivirus, disk defragmenter, disk cleanup, backup and restore, file compression such as ZIP, and file managers. Utilities are system software, not applications — a favourite one-line trap.
• Open source versus proprietary. Open-source software gives you the source code with freedom to study, modify and redistribute — Linux, LibreOffice, Mozilla Firefox, Apache, MySQL, GIMP. Proprietary or licensed software keeps the source code closed — Microsoft Windows, MS Office, Adobe Photoshop, Tally. Freeware is free to use but not necessarily open source, and shareware is free only for a trial period.

The operating system is the interface between user, application and hardware. Its six textbook functions are process management, memory management, file management, device management, security and providing the user interface. Examples: Windows, Linux, Unix, macOS for computers and Android, iOS for phones; MS-DOS was the older command-line system. A GUI works through windows, icons, menus and a pointer, while a CLI needs typed commands. Multiprogramming keeps several programs in memory; multitasking lets one user run several tasks; time-sharing gives many users a slice of CPU time in turn; a real-time OS guarantees a response deadline, as in air-traffic control.

MS Word is a word processor; its default file extension is .docx. Formatting lives on the Home tab (font, size, bold, alignment, bullets, line spacing); Insert carries tables, pictures, page numbers and header and footer; Mailings carries mail merge, which combines one letter template with a data list to produce many personalised letters; Review carries spelling and grammar (also F7), word count, thesaurus (Shift+F7), comments and Track Changes, which records every insertion and deletion so a reviewer can accept or reject them. Layout handles margins, orientation and columns; References handles table of contents, footnotes and citations.

• MS Excel — the file, the sheet, the cell. A workbook (.xlsx) contains worksheets; each cell is named by its column letter and row number, as in B7. A modern worksheet has 1,048,576 rows and 16,384 columns, the last being XFD. Every formula must begin with an equals sign.
• Relative, absolute and mixed referencing. A1 is relative and shifts when you copy the formula; $A$1 is absolute and never shifts; $A1 and A$1 are mixed, locking only the column or only the row. The F4 key cycles a reference through these four states while you edit.
• Core functions. SUM adds a range; AVERAGE gives the mean; COUNT counts only numeric cells while COUNTA counts every non-empty cell including text, and COUNTBLANK counts empty ones; MAX and MIN give extremes; IF takes the form IF(condition, value if true, value if false); VLOOKUP searches the leftmost column of a table and returns a value from a column to its right, given as IF-like arguments lookup value, table range, column number and an optional exact-or-approximate flag.
• Charts and views. Use a pie chart for the share of parts in one whole, a line chart for a trend over time, a column or bar chart for comparison across categories, and a scatter chart for the relation between two variables. Charts are inserted from the Insert tab. Freeze Panes on the View tab keeps the heading row or column visible while you scroll — do not confuse it with Split, which creates independent panes. Common error values are #DIV/0! for division by zero, #NAME? for a misspelt function, #REF! for a deleted reference and #VALUE! for the wrong data type.
• MS PowerPoint. Files are .pptx. The Slide Master stores the common design — change a font there and every slide changes at once. Transitions are the effects that play when you move from one slide to the next; Animations are the effects applied to objects inside a single slide. F5 starts the show from the first slide and Shift+F5 from the current slide; Esc ends it. Slide Sorter view shows thumbnails for reordering, and Rehearse Timings records how long you spend per slide.

• Network by geographical spread. LAN covers one building or campus and is the fastest and cheapest; MAN covers a city, as a cable-television or municipal fibre network does; WAN spans states and countries, and the Internet is the largest WAN of all. A PAN is a personal network of a few metres, as with Bluetooth.
• Topologies. In a bus topology every node shares one backbone cable, so a break in the backbone stops everything. In a star topology every node connects to a central hub or switch — the most common layout today, easy to troubleshoot, but the hub is a single point of failure. A ring passes data node to node in one direction. A mesh connects every node to every other, giving the highest reliability at the highest cost. Tree and hybrid combine these.
• Connecting devices. A hub broadcasts to all ports; a switch sends the frame only to the intended port; a router joins two different networks and chooses paths; a bridge joins two segments of the same network; a gateway connects networks using different protocols; a modem modulates and demodulates signals between digital and analog form.
• Addressing and naming. An IP address identifies a machine: IPv4 is 32 bits written as four numbers from 0 to 255, and IPv6 is 128 bits, created because IPv4 addresses ran short. DNS (Domain Name System) translates a readable domain name into that IP address — it is the phone book of the Internet. A URL has the form protocol, then domain name, then path. Top-level domains include .com for commercial, .org for organisations, .edu, .gov, .net and the country code .in, with .ac.in and .nic.in used in India.
• Browser versus search engine — the most missed distinction. A browser is software installed on your device that displays web pages: Chrome, Firefox, Edge, Safari, Opera. A search engine is a website you visit through a browser to find pages: Google, Bing, Yahoo, DuckDuckGo. Chrome is not a search engine and Google Search is not a browser.
• Bandwidth, ISP, cookies and cloud. Bandwidth is the data-carrying capacity of a link, measured in bits per second and its multiples Kbps, Mbps and Gbps — note that it measures capacity, not speed of light. An ISP (Internet Service Provider) sells you the connection. Cookies are tiny text files a website stores in your browser to remember your session and preferences; they are not malware, though tracking cookies raise privacy concerns. Cloud computing delivers computing over the Internet in three service models — IaaS (raw servers and storage), PaaS (a platform to build on) and SaaS (finished software such as web mail) — and three deployment models, public, private and hybrid.

On e-mail, an address has the form user name, then the @ sign, then the domain. To carries the primary recipients. CC (carbon copy) sends a copy that every recipient can see. BCC (blind carbon copy) sends a copy whose address no other recipient can see — the correct choice when you mail a hundred candidates and must not leak their addresses to one another. Attachments have a size limit set by the mail service, so large files are shared as cloud links instead. Unsolicited bulk mail is spam and is filtered into a junk folder. Reply answers the sender, Reply All answers everyone in To and CC, and Forward sends the message on to someone new. Drafts hold unsent mail, and Outbox holds mail waiting to go out.

• Phishing, vishing and smishing are all social engineering — fooling a human instead of breaking a machine. Phishing uses a fake e-mail or website that looks like your bank; vishing uses a voice call claiming to be from the bank or a KYC officer; smishing uses an SMS with a malicious link. In all three, the fraudster wants your password, card number, CVV or OTP. No bank, no exam body and no government office ever asks for an OTP.
• Firewall is a hardware or software barrier that inspects traffic entering and leaving a network and blocks whatever violates the rules. It is a gatekeeper, not a virus remover. Antivirus software scans, detects, quarantines and removes malware, and is useful only when its virus definitions are kept updated.
• Encryption converts readable plaintext into unreadable ciphertext with a key. Symmetric encryption uses the same key at both ends; asymmetric or public-key encryption uses a public key to lock and a private key to unlock. A digital signature applies the sender private key to a message digest, and so provides authentication, integrity and non-repudiation. In India, digital signature certificates are issued by licensed Certifying Authorities supervised by the Controller of Certifying Authorities.
• Password and account hygiene. A strong password is long, mixes upper case, lower case, digits and symbols, avoids dictionary words, names and dates of birth, and is different on every site. Add two-factor authentication, where a password is combined with a second factor such as an OTP, an authenticator app or a fingerprint, so a stolen password alone is useless. Never bank on public Wi-Fi, log out of shared computers, and check for the HTTPS padlock before entering credentials.

A database is an organised collection of related data, and a DBMS is the software that stores, retrieves and protects it — Oracle, MySQL, PostgreSQL, Microsoft SQL Server and MS Access are the usual examples. In the relational model, proposed by E. F. Codd, data sit in tables: a row is a record or tuple, a column is a field or attribute. A primary key uniquely identifies each row and can never be null or duplicated; a foreign key in one table points to the primary key of another and thus links them; a candidate key is any column set that could serve as the primary key. Queries are written in SQL, whose DDL commands CREATE, ALTER and DROP change structure while DML commands SELECT, INSERT, UPDATE and DELETE work on data.

On file handling, remember that a folder (directory) contains files and other folders, and the path is its address on the disk. Deleting a file sends it to the Recycle Bin, from which it can be restored; Shift+Delete removes it permanently. Cut, copy and paste operate through the clipboard, a temporary holding area. A shortcut icon only points to a file, so deleting the shortcut leaves the original untouched.

• Digital India rests on three vision areas — digital infrastructure as a utility for every citizen, governance and services on demand, and digital empowerment of citizens — delivered through nine pillars that include Broadband Highways, Universal Access to Mobile Connectivity, the Public Internet Access Programme, e-Kranti, Information for All, Electronics Manufacturing, IT for Jobs and Early Harvest Programmes.
• Flagship platforms. DigiLocker stores verified documents such as mark sheets and driving licences in a cloud account whose copies are legally at par with originals; UMANG gathers hundreds of government services into one app; MyGov is the citizen-engagement platform; BharatNet lays optical fibre to gram panchayats; e-Sign allows Aadhaar-based online signing.
• Digital payments and identity. Aadhaar is the 12-digit unique identity issued by UIDAI; UPI, built by the National Payments Corporation of India, lets money move instantly between bank accounts using a virtual payment address, and BHIM is its reference app. The JAM trinity — Jan Dhan bank account, Aadhaar and Mobile — is what makes Direct Benefit Transfer possible.
• Models of e-governance. G2C serves citizens (paying a bill, booking a ticket, filing a return); G2B serves business (licences, tenders, GST filing, the GeM portal); G2G connects one government office to another (inter-departmental data sharing); G2E serves employees (pay slips, service records, leave applications).