Maharashtra HSC IT Science cheat sheet

Data is raw unprocessed facts; information is processed data that supports decisions; knowledge applies experience to information.

Bit = binary digit (0 or 1); 1 byte = 8 bits; 1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.

Number system bases: binary 2, octal 8, decimal 10, hexadecimal 16; hex digits are 0-9 and A-F.

Binary to decimal: multiply each bit by 2 raised to its position (rightmost = 2^0) and sum; 1101 = 13.

Decimal to binary: repeatedly divide by 2 and read remainders bottom-to-top; decimal to octal/hex divide by 8/16 instead.

Group binary bits in fours from the right to convert to hex (1101 0110 = D6); group in threes for octal.

Logic gates: AND outputs 1 only if all inputs are 1; OR outputs 1 if any input is 1; NOT inverts; XOR outputs 1 for odd number of 1s.

Hardware is physical (CPU, RAM, I/O devices); software is logical (system software such as OS and utilities, application software such as editors and browsers).

CPU cycle = fetch, decode, execute, store; ALU performs arithmetic and logic, control unit sequences instructions, registers hold current data.

An operating system is system software that manages hardware, provides an interface to the user, and allocates CPU, memory, and I/O resources.

Functions: process management, memory management, file management, device management, security, and user interface.

Batch OS runs jobs in groups without interaction; time-sharing OS gives each user a time slice; real-time OS guarantees response within a deadline.

Single-user OS serves one user at a time; multi-user OS allows concurrent users; multiprogramming keeps several jobs in memory, multiprocessing uses more than one CPU.

Process states: new, ready, running, waiting (blocked), terminated; a process moves ready to running when the scheduler dispatches it.

Scheduling goals: maximize CPU utilization and throughput, minimize turnaround time, waiting time, and response time.

FCFS is non-preemptive and suffers the convoy effect; SJF gives minimum average waiting time but needs burst-time knowledge; round robin is preemptive with a fixed time quantum.

Deadlock needs four conditions together: mutual exclusion, hold and wait, no preemption, circular wait; breaking any one prevents it.

GUI uses windows, icons, menus, and pointer; CLI accepts typed commands; a file is a named collection of related records stored on secondary storage.

HTML defines structure; CSS defines presentation; a tag is written as and an element is the opening tag, content, and closing tag together.

Required document skeleton: , , (metadata, ), then <body> for visible content.</p>

Heading tags

is a paragraph;
and

Lists:

unordered with bullets,
ordered with numbering, definition list with term and description;
1. is the list item.

Links use text; target="_blank" opens a new tab; internal links use #id to jump to an element.

Images use ; alt text is required for accessibility and displays when the image fails to load.

Tables use

Forms use

CSS rule syntax: selector { property: value; }; selectors include element (p), class (.note), id (#main), and descendant (div p); class is reusable, id is unique.

IoT is a network of physical devices with sensors and actuators that collect and exchange data over the internet without human intervention.

Typical IoT architecture layers: sensing (devices), network (connectivity), and application (services and analytics).

Examples: smart home appliances, wearable health monitors, smart agriculture soil sensors, connected vehicles, industrial machine monitoring.

Cloud computing delivers computing resources on demand over a network; essential traits are on-demand self-service, broad network access, resource pooling, rapid elasticity, measured service.

Service models: IaaS supplies virtual machines and storage, PaaS supplies a development and runtime platform, SaaS supplies ready applications through a browser.

Deployment models: public cloud (open to all), private cloud (single organization), hybrid cloud (combination), community cloud (shared by related organizations).

AI is the simulation of human intelligence by machines; machine learning learns patterns from data rather than explicit rules; deep learning uses multi-layer neural networks.

AI subfields: natural language processing, computer vision, robotics, expert systems, speech recognition; training data quality determines model accuracy.

5G is the fifth-generation mobile network: peak data rates around 20 Gbps, latency near 1 ms, and high device density; features are enhanced mobile broadband, ultra-reliable low-latency communication, and massive machine-type communication.

JavaScript can be embedded with in the head or body, or linked externally with .

var is function-scoped and hoisted; let and const are block-scoped, and const must be initialized and cannot be reassigned.

Data types: number, string, boolean, null, undefined, object; typeof returns the type name; == compares after type conversion, === compares value and type.

Functions are declared as function name(params){...} or as expressions and arrow functions; return sends a value back to the caller.

DOM access: document.getElementById(), document.querySelector(), document.getElementsByClassName(); textContent or innerHTML changes content.

Events attach with element.addEventListener('click', handler) or inline onclick; common events are click, change, submit, mouseover, keyup.

Arrays use zero-based indexing; push adds to the end, pop removes the last, length gives the count; objects store key: value pairs read with dot or bracket notation.

CSS box model from inside out: content, padding, border, margin; box-sizing: border-box makes width include padding and border.

CSS positioning values: static (default), relative (offset from normal position), absolute (relative to nearest positioned ancestor), fixed (relative to viewport), sticky.

Media queries use @media (max-width: 600px) {...} to apply rules only when the condition holds, enabling responsive layouts.

PHP is a server-side scripting language; code runs on the web server and the browser receives only the generated HTML output.

PHP blocks open with ; statements end with a semicolon; variables start with $ and need no type declaration.

Strings: single quotes take text literally; double quotes interpolate variables; the dot operator (.) concatenates strings.

Arrays: indexed arrays use numeric keys starting at 0; associative arrays use named keys; foreach($arr as $key => $value) iterates over both.

Superglobals: $_GET for query-string data, $_POST for form-body data, $_REQUEST for both, $_SESSION for session data, $_COOKIE for cookies, $_SERVER for server details.

Form handling pattern: method="post" on the form, then read $_POST['field']; use isset() to check existence and htmlspecialchars() to prevent XSS.

MySQL connection with mysqli: $conn = new mysqli($host,$user,$pass,$db); then $conn->query($sql) to run SQL and $conn->close() to disconnect.

Sessions: call session_start() before any output, store values in $_SESSION, and destroy them with session_destroy() on logout.

include includes a file and continues on failure with a warning; require stops execution with a fatal error if the file is missing; include_once and require_once prevent duplicates.

A database is an organized collection of related data; a DBMS is software that stores, retrieves, and manages that data; RDBMS stores data in related tables.

Primary key uniquely identifies each row and cannot be null; foreign key references a primary key in another table and enforces referential integrity.

Candidate key is any column set that can uniquely identify a row; the chosen candidate key becomes the primary key; alternate keys are the remaining candidates.

Normalization: 1NF removes repeating groups (atomic values), 2NF removes partial dependency on part of a composite key, 3NF removes transitive dependency on non-key columns.

DDL defines structure: CREATE, ALTER, DROP, TRUNCATE; DML manipulates rows: INSERT, UPDATE, DELETE, SELECT; DCL controls rights: GRANT, REVOKE; TCL handles transactions: COMMIT, ROLLBACK.

SELECT syntax order: SELECT columns FROM table WHERE condition GROUP BY columns HAVING condition ORDER BY columns ASC|DESC.

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

Operators: =, <>, >, <, BETWEEN, IN, LIKE (with % and _ wildcards), IS NULL; logical AND, OR, NOT combine conditions.

Joins: INNER JOIN returns matching rows only; LEFT JOIN keeps all left rows with NULLs for unmatched right columns; RIGHT JOIN mirrors it.

DELETE removes rows and can be rolled back; DROP removes the table structure itself; TRUNCATE empties all rows quickly and cannot use WHERE.

The Information Technology Act, 2000 is India's primary cyber law; it was amended in 2008 and gives legal recognition to electronic records and digital signatures.

Section 43 covers unauthorized access, damage, and disruption of computers; Section 66 covers computer-related offences including identity theft (66C) and cheating by personation (66D).

Section 66E punishes violation of privacy by capturing or publishing private images; Section 67 covers publishing obscene material in electronic form.

Section 72 deals with breach of confidentiality and privacy; Section 65 covers tampering with computer source documents.

Cyber crime categories: hacking, phishing, identity theft, cyberstalking, ransomware, denial-of-service, data breach, and financial fraud.

Malware types: virus attaches to files, worm self-replicates across networks, trojan disguises itself as useful software, spyware covertly collects data, ransomware encrypts data for payment.

Phishing uses fake messages or sites to steal credentials; pharming redirects to fake sites via DNS manipulation; social engineering manipulates people rather than systems.

Security goals are confidentiality, integrity, and availability (CIA triad); authentication verifies identity, authorization controls permitted actions.

Firewall filters network traffic by rules; antivirus detects known malicious patterns; encryption converts plaintext to ciphertext using a key; digital signature verifies authenticity and integrity.