Maharashtra HSC IT Commerce cheat sheet

Data is raw unorganised facts; information is processed data that supports decisions; knowledge applies information with experience.

IPOS cycle: Input → Process → Output → Storage. Every computing task can be decomposed into these four stages.

Hardware categories: input devices, output devices, CPU (ALU + Control Unit + registers), primary memory (RAM/ROM), secondary storage.

RAM is volatile and holds currently running programs; ROM is non-volatile and holds firmware such as BIOS. Cache sits between CPU and RAM for speed.

Units: 1 nibble = 4 bits, 1 byte = 8 bits, 1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.

Number systems: binary base 2, octal base 8, decimal base 10, hexadecimal base 16. Hex digits A–F represent 10–15.

Binary to decimal: multiply each bit by 2 raised to its position from the right, starting at 2^0. Decimal to binary: repeatedly divide by 2 and read remainders bottom-up.

Software types: system software (OS, utilities, device drivers) versus application software (general-purpose like word processors, and customised/tailor-made).

Open source software publishes source code for modification (e.g., Linux, LibreOffice); proprietary software restricts source access under licence.

An operating system is system software acting as an interface between user and hardware, managing processes, memory, files, devices and security.

Functions: process management, memory management, file management, device management, security, and providing a 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 (hard vs soft).

Distributed OS coordinates multiple networked computers as one system; multiprocessing OS uses two or more CPUs in one machine.

GUI provides icons, windows and menus; CLI accepts typed commands (e.g., DOS, Bash). GUI is easier for novices; CLI is faster and scriptable.

Mobile OS examples: Android (Linux kernel based), iOS. Desktop examples: Windows, Linux distributions, macOS.

Multitasking switches the CPU rapidly between processes; multithreading runs multiple threads inside one process sharing its memory.

A file system organises data into files and directories; FAT, NTFS and ext4 differ in journaling, permissions and maximum volume size.

Booting: POST runs hardware checks, then the bootloader loads the kernel into RAM and hands control to the OS.

HTML structure: , , (title, meta, linked CSS) and (visible content). Tags are paired except void elements like
, ,

Core tags: headings

,

Attributes always sit in the opening tag as name="value"; href sets link target, src sets resource path, alt gives alternative text for accessibility.

CSS syntax: selector { property: value; }. Inline style uses the style attribute; internal CSS sits in

Selector types: element (p), class (.note), id (#header), descendant (div p), grouping (h1, h2), and pseudo-classes such as :hover and :first-child.

The box model, inside out: content → padding → border → margin. width/height apply to content unless box-sizing: border-box is set.

Cascade order of precedence: inline style beats internal and external; among equal specificity the later rule wins; !important overrides normal declarations.

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

Flexbox: display:flex on the container, then justify-content for main-axis alignment and align-items for cross-axis alignment.

IoT architecture layers: sensing/perception (sensors, actuators) → network (Wi-Fi, Bluetooth, LoRa, 5G) → middleware/data processing → application layer.

IoT characteristics: connectivity, sensing, actuation, heterogeneity, huge scale, and dynamic change. Examples: smart home, wearables, smart agriculture, connected vehicles.

Cloud service models: IaaS supplies virtual machines and storage; PaaS supplies a runtime and development platform; SaaS supplies ready applications (email, CRM).

Cloud deployment models: public, private, community and hybrid. Essential traits are on-demand self-service, broad network access, resource pooling, rapid elasticity, measured service.

AI subfields: machine learning, deep learning (multi-layer neural networks), natural language processing, computer vision, robotics and expert systems.

AI types by capability: narrow/weak AI (task-specific, current systems), general AI, and strong/super AI (hypothetical).

ML learning types: supervised (labelled data, classification/regression), unsupervised (clustering, association), and reinforcement (reward-based trial and error).

5G key parameters: peak data rate up to 20 Gbps, latency around 1 ms, high device density (about 1 million devices per km²).

5G enablers: enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC), and massive machine-type communication (mMTC).

Variable declarations: var is function-scoped and hoisted as undefined; let and const are block-scoped; const forbids reassignment but not mutation of object contents.

Data types: number, string, boolean, null, undefined, object, symbol, bigint. typeof null returns "object"; arrays and functions are objects.

Functions are first-class: they can be stored in variables, passed as arguments (callbacks) and returned. Arrow functions (a, b) => a + b do not bind their own this.

DOM selection: document.getElementById, querySelector, querySelectorAll. Events attach with addEventListener("click", handler); the handler receives an event object.

Event flow: capture phase travels down to the target, then bubbling travels up. stopPropagation halts further flow; preventDefault cancels the default browser action.

Array methods: push/pop change the end, shift/unshift change the start; map transforms, filter selects, reduce accumulates, forEach iterates without returning a new array.

Template literals use backticks and ${expression} interpolation, and support multi-line strings.

JSON.parse converts a JSON string to an object; JSON.stringify converts an object to a JSON string. Both throw or drop data on invalid input.

Promises have three states: pending, fulfilled, rejected; .then handles success, .catch handles failure, and async/await is syntactic sugar over promises.

PHP tags: embed server code in HTML; PHP files usually use the .php extension and are executed on the server, outputting plain HTML to the browser.

Variables start with $ (e.g., $name) and are loosely typed. Strings concatenate with the dot operator: $a . $b.

Superglobals: $_GET (query string), $_POST (form body), $_REQUEST (both), $_SESSION, $_COOKIE, $_SERVER, $_FILES.

Form handling: method="post" sends data in the request body; method="get" appends it to the URL. Use isset($_POST['field']) before reading a value.

Sessions: session_start() must be called before output; store data in $_SESSION; session_destroy() clears the session.

Cookies: setcookie(name, value, expiry) must run before any HTML output; cookies live client-side, sessions store data server-side.

Database connection with MySQLi: $conn = new mysqli($host, $user, $pass, $db); check $conn->connect_error; run $conn->query($sql); fetch rows with fetch_assoc().

Prepared statements separate SQL from data using placeholders, preventing SQL injection: $stmt = $conn->prepare("SELECT * FROM t WHERE id=?"); then bind_param and execute.

String and array functions: strlen, str_replace, strtolower, implode, explode, count, in_array, and foreach ($arr as $key => $value).

DBMS advantages over flat files: reduced redundancy, controlled consistency, concurrent access, backup/recovery, and data independence.

Relational model terms: relation = table, tuple = row/record, attribute = column/field, degree = number of columns, cardinality = number of rows.

Keys: primary key uniquely identifies a row and cannot be NULL; foreign key references another table's primary key; candidate keys are possible primary keys.

DDL commands define structure: CREATE, ALTER, DROP, TRUNCATE. DML commands manipulate data: SELECT, INSERT, UPDATE, DELETE.

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

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

Joins: INNER returns matching rows only; LEFT returns all left rows plus matches; RIGHT mirrors it; FULL returns all rows from both sides.

Constraints: NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK, DEFAULT. They enforce validity at the database level.

Normalisation: 1NF removes repeating groups; 2NF removes partial dependency on part of a composite key; 3NF removes transitive dependency on non-key attributes.

E-commerce models: B2B (business to business), B2C (business to consumer), C2C (consumer to consumer via marketplaces), and B2G/G2C variants.

E-commerce transaction phases: pre-sale (search, catalogue), sale (order, payment), and post-sale (delivery, support, returns).

Payment mechanisms: credit/debit cards, net banking, UPI, digital wallets, and cash on delivery. Payment gateways encrypt card data in transit.

E-commerce benefits: wider reach, 24×7 operation, lower overhead; challenges: security of payments, delivery logistics, returns, and trust.

CIA triad: Confidentiality (only authorised access), Integrity (data unaltered), Availability (systems reachable when needed).

Malware categories: virus (attaches to files), worm (self-replicates over networks), trojan (disguised as legitimate), ransomware (encrypts data for payment), spyware (secretly collects data).

Attack types: phishing (fake messages harvesting credentials), pharming (DNS redirection), man-in-the-middle, DoS/DDoS (flooding a service), SQL injection, and social engineering.

Defences: strong passwords with MFA, updated antivirus and firewalls, HTTPS/TLS encryption, regular backups, and never sharing OTPs or passwords.

Cyber law in India: the Information Technology Act, 2000 governs electronic records, digital signatures and cyber offences; sections cover unauthorised access and data tampering.