Kerala Plus Two Computer Applications (DHSE) cheat sheet

Decimal to binary: repeatedly divide by 2, collect remainders from last to first; e.g., 25₁₀ = 11001₂.

Binary to decimal: sum each bit times its positional weight 2ⁿ, starting from n=0 at the rightmost bit.

Octal uses digits 0–7; group binary bits in threes from the radix point: 110101₂ = 65₈.

Hexadecimal uses 0–9 and A–F; group binary bits in fours: 10101111₂ = AF₁₆.

1's complement: flip every bit. 2's complement: flip every bit then add 1; equals 1's complement + 1.

Subtraction via 2's complement: A − B = A + (2's complement of B), discard the final carry out of the MSB.

n bits represent unsigned integers 0 to 2ⁿ−1; signed 2's complement range is −2ⁿ⁻¹ to 2ⁿ⁻¹−1.

1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB; a nibble is 4 bits, a byte is 8 bits.

ASCII-7 encodes 128 characters; extended ASCII uses 8 bits (256); Unicode (UTF-8/UTF-16) covers all scripts.

Von Neumann architecture: CPU (ALU + control unit + registers), memory, input/output, and a shared bus; instructions and data share memory.

Primary memory is volatile (RAM) or ROM; secondary storage (HDD/SSD/optical) is non-volatile and slower but larger.

Cache (L1/L2/L3) is faster and smaller than RAM; registers are fastest; access time order: register < cache < RAM < secondary.

System software = OS + utilities + language translators (compiler, interpreter, assembler); application software is task-specific.

Compiler translates the whole program before execution; interpreter translates and executes line by line; assembler converts assembly to machine code.

OS functions: process management, memory management, file system management, device I/O management, and user interface.

Multiprogramming keeps several jobs in memory; multitasking time-slices the CPU; multiprocessing uses two or more CPUs.

Open-source examples: Linux, GNU, BSD; proprietary examples: Windows, macOS. Firmware such as BIOS/UEFI is stored in ROM/flash.

Plug and Play and device drivers let the OS detect and control hardware without manual resource configuration.

Transmission modes: simplex (one direction only), half-duplex (both directions, not simultaneously), full-duplex (both simultaneously).

Topologies: bus (single backbone), star (central hub/switch), ring (closed loop), mesh (n(n−1)/2 links), tree (hierarchical).

OSI has 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, Application (bottom to top).

TCP/IP model layers: Network Access (Link), Internet, Transport, Application.

IPv4 address = 32 bits written as four dotted decimal octets; IPv6 = 128 bits written in hexadecimal groups.

Private IPv4 ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16; loopback is 127.0.0.1.

Bandwidth is capacity in bits per second; latency is delay; a protocol is the agreed set of rules for exchange.

Guided media: twisted pair, coaxial, fibre optic. Unguided media: radio, microwave, infrared, satellite.

Switching types: circuit switching (dedicated path), packet switching (store-and-forward packets), message switching.

URL parts: protocol://host:port/path?query#fragment; e.g., https://example.com/page?id=1.

DNS maps domain names to IP addresses; the resolver queries root, TLD, and authoritative name servers.

HTTP is stateless request/response; HTTPS = HTTP over TLS on port 443; HTTP default port 80.

Email protocols: SMTP sends (port 25), POP3 retrieves (port 110), IMAP synchronises (port 143).

FTP uses ports 20 (data) and 21 (control); SSH uses port 22; Telnet uses port 23.

A cookie is a small text file stored by the browser; a session stores state on the server and identifies the client by a session ID.

Web browsers render HTML/CSS/JS; web servers (Apache, Nginx) serve resources; search engines index the web via crawlers.

ISP = Internet Service Provider; backbone networks interconnect ISPs; a gateway/router forwards packets between networks.

IPv4 vs IPv6: IPv4 is 32-bit and exhaustible; IPv6 is 128-bit with built-in address autoconfiguration.

HTML document skeleton: , , , ; belongs in <head>.</p>

Headings

paragraph;
line break;

Links: text; target="_blank" opens a new tab; mailto: launches the mail client.

Lists:

unordered,
ordered,
1. item; // definition list.

Tables:

Forms:

CSS syntax: selector { property: value; }; selectors include element, .class, #id, and descendant (a b).

CSS inclusion: inline style attribute, internal

Box model: content → padding → border → margin; box-sizing: border-box includes padding and border in width.

Word processor features: text entry/editing, formatting, spell/grammar check, find & replace, tables, mail merge, print preview.

Character formatting changes font, size, bold/italic/underline, colour; paragraph formatting changes alignment, indents, spacing, line spacing.

Alignment options: left, centre, right, justify; line spacing values include single, 1.5, double, and exact points.

Styles apply consistent formatting; the Navigation pane and outline view use heading styles to build a table of contents.

Mail merge combines a main document with a data source to produce personalised letters/labels.

Track Changes records edits; comments annotate without changing text; Compare merges two versions.

Headers/footers repeat on every page; section breaks allow different headers, orientation, or page numbering per section.

Tables in word processors support merged cells, borders/shading, and formulas such as =SUM(ABOVE).

PDF export preserves layout across devices; .docx is the editable format, .txt keeps plain text only.

Cell reference types: relative A1, absolute $A$1, mixed $A1 or A$1; $ locks the row or column during copy/fill.

Formula starts with =; operators: + − * / ^ and comparison = <> > < >= <=; text concatenation uses &.

Functions: SUM, AVERAGE, COUNT, COUNTA, MAX, MIN, IF(condition, true, false), ROUND, and nested IFs.

Lookup functions: VLOOKUP(value, table, col_index, FALSE) for exact match; HLOOKUP searches the first row.

COUNT counts numeric cells; COUNTA counts non-empty cells; COUNTIF counts cells matching a criterion.

A chart plots selected ranges; column/bar compare categories, line shows trends, pie shows proportions.

Sorting orders rows by one or more keys; filtering hides rows not matching criteria; conditional formatting changes appearance by rule.

Presentations: slide layouts and masters control placeholders; transitions apply between slides; animations apply to objects.

Slide show shortcuts: F5 start from beginning, Shift+F5 start from current slide, Esc end; speaker notes are not shown to the audience.

Relational model: relation (table), tuple (row), attribute (column), domain (allowed values), degree (number of attributes), cardinality (number of tuples).

Keys: super key, candidate key, primary key (unique + NOT NULL), alternate key, foreign key (references a primary key), composite key.

Integrity: entity integrity (no NULL primary key), referential integrity (foreign key values must exist in the referenced table), domain integrity.

Normalisation: 1NF atomic values; 2NF no partial dependency on part of a composite key; 3NF no transitive dependency.

SQL categories: DDL (CREATE, ALTER, DROP), DML (INSERT, UPDATE, DELETE), DQL (SELECT), DCL (GRANT, REVOKE), TCL (COMMIT, ROLLBACK).

SELECT columns FROM table WHERE condition GROUP BY column HAVING condition ORDER BY column [ASC|DESC];

Aggregate functions: COUNT, SUM, AVG, MIN, MAX; WHERE filters rows before grouping, HAVING filters groups after grouping.

Joins: INNER JOIN returns matching rows; LEFT/RIGHT OUTER JOIN keeps unmatched rows from one side; CROSS JOIN is the Cartesian product.

Constraints: PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, CHECK, DEFAULT; ALTER TABLE adds or drops them.

Algorithm properties: finiteness, definiteness, input, output, effectiveness; a flowchart uses standard symbols (oval start/end, parallelogram I/O, rectangle process, diamond decision).

Control structures: sequence, selection (if/if-else/switch), iteration (while, do-while, for).

while checks the condition before the body (may run zero times); do-while checks after (runs at least once).

Searching: linear search is O(n); binary search requires sorted data and is O(log n).

Sorting: bubble, selection, insertion are O(n²) comparisons; merge sort and quicksort average O(n log n).

Time complexity order: O(1) < O(log n) < O(n) < O(n log n) < O(n²) < O(2ⁿ).

Recursion solves a problem by calling itself with a smaller input and needs a base case to terminate.

Variables hold values in memory; a constant cannot be reassigned; a parameter passes data into a function.

Trace tables record variable values after each step to verify an algorithm by hand.

C program structure: #include directives, function prototypes, int main(void) { ... return 0; }.

Data types: char (1 byte), int (usually 4), float (4), double (8); sizeof gives size in bytes.

Formats: %d int, %f float/double, %c char, %s string, %lf double in scanf; & is required for scanf variables except arrays.

Operators: arithmetic + − * / %, relational == != < >, logical && || !, assignment =, increment ++/--, ternary ?:.

Integer division truncates: 7/2 = 3; 7%2 = 1; use float casts for fractional results.

Control: if/else if/else, switch (integer/char cases with break), for(init; test; update), while, do-while.

Arrays are zero-indexed: int a[5] holds a[0]..a[4]; strings are char arrays ending with the null character '\0'.

Functions: return_type name(parameters) { ... }; pass by value copies the argument; use pointers for pass by reference.

Pointers store addresses: int *p = &x; *p dereferences; malloc/free manage dynamic memory.

E-governance services include online certificates, land records, tax filing, and public grievance portals.

E-learning uses LMS platforms, MOOCs, and video lectures; blended learning combines online and classroom instruction.

E-commerce models: B2B, B2C, C2C, C2B, and G2C for government services.

Telemedicine delivers remote consultation and diagnostics; e-health stores electronic health records.

Digital India, Ayushman Bharat, and UPI are Indian initiatives; UPI enables instant bank-to-bank mobile payments.

IT-enabled services (ITES) include BPO, KPO, call centres, and data processing; they create employment and foreign exchange.

Digital divide refers to unequal access to ICT across regions and groups; ICT can widen or narrow it depending on policy.

Automation and AI change job roles; reskilling and digital literacy are policy responses.

Intellectual property in ICT covers software copyright, patents, and trademarks; unauthorised copying is infringement.

CIA triad: confidentiality (secrecy), integrity (accuracy), availability (access when needed).

Malware types: virus (attaches to files), worm (self-replicates over networks), trojan (disguised), ransomware (encrypts and demands payment), spyware (collects data).

Phishing tricks users into revealing credentials via fake messages; pharming redirects to fake sites via DNS or hosts manipulation.

Authentication factors: something you know (password), something you have (OTP/token), something you are (biometrics).

Encryption converts plaintext to ciphertext with a key; symmetric uses one shared key, asymmetric uses a public/private key pair.

Firewalls filter network traffic by rules; antivirus scans for known malware signatures; updates patch vulnerabilities.

Cyber laws in India: IT Act 2000 (amended 2008) covers electronic records, digital signatures, and cyber offences; IPC sections apply to conventional crimes.

Ethical practice: do not access systems without authorisation, do not plagiarise or pirate software, respect privacy and netiquette.

Strong passwords are long, mixed, and unique; enable two-factor authentication; back up data to recover from ransomware.