Maharashtra HSC Computer Technology (Vocational) cheat sheet

Von Neumann architecture: CPU (ALU + control unit + registers), memory, input, output, and buses connecting them; instructions and data share the same memory.

CPU cycle: Fetch → Decode → Execute → Store (write-back); clock speed in GHz sets how many cycles per second, not how much work per cycle.

Memory hierarchy by speed and cost: registers > cache (L1/L2/L3) > RAM > SSD/HDD > optical/tape; capacity and access time move in opposite directions.

Primary memory is volatile (RAM: SRAM in cache, DRAM in main memory); ROM is non-volatile and holds firmware/BIOS bootstrap code.

Secondary storage: HDD uses magnetic platters and is measured in RPM; SSD uses flash NAND, has no moving parts, and gives lower latency.

Ports and buses: USB, HDMI, VGA, SATA, PCIe; USB is hot-swappable and supplies power; HDMI carries digital video and audio together.

Input devices convert real-world data to digital form (keyboard, mouse, scanner, mic); output devices do the reverse (monitor, printer, speaker); a touchscreen is both.

Units: 1 byte = 8 bits; 1 KB = 1024 B, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB (binary prefixes).

OS roles: process management, memory management, file system management, device (I/O) management, and providing the user interface.

Batch vs time-sharing vs real-time OS: batch runs jobs without interaction, time-sharing gives many users interactive slices, RTOS guarantees response deadlines.

GUI vs CLI: a command line accepts typed commands (e.g., dir, copy, del) and can be scripted; a GUI uses windows, icons, menus, and a pointer.

File name = base name + extension; the extension suggests the type (.txt text, .docx document, .jpg image, .mp3 audio, .mp4 video, .exe executable, .html web page).

Path types: absolute path starts from the root (e.g., C:\Users\Name\file.txt); relative path is resolved from the current working directory.

Common file operations: create, open, read, write, append, rename, copy, move, delete; deleting to a recycle bin is recoverable, permanent delete (Shift+Del) is not.

File attributes and permissions: read-only, hidden, system, archive; permissions are usually granted per user/group as read, write, execute.

Disk utilities: formatting prepares a volume, defragmentation rearranges HDD fragments, and disk cleanup removes temporary files; defragmentation is not needed for SSDs.

Bases in use: binary (2), octal (8), decimal (10), hexadecimal (16); hexadecimal digits A–F stand for 10–15.

Binary to decimal: multiply each bit by 2 raised to its position power (rightmost position = 0) and add; e.g., 1011₂ = 8+0+2+1 = 11₁₀.

Decimal to binary: repeatedly divide by 2 and read remainders bottom-to-top; for fractions, repeatedly multiply the fractional part by 2 and read integer parts top-to-bottom.

Binary ↔ octal: group bits in threes from the radix point; binary ↔ hexadecimal: group in fours; pad with zeros on the outer sides only.

Hexadecimal to decimal: multiply each digit by 16 raised to its position power and add; e.g., 2F₁₆ = 2×16 + 15 = 47₁₀.

1's complement: invert every bit; 2's complement: invert every bit then add 1. 2's complement represents negatives and has a single zero.

Signed 8-bit range in 2's complement is −128 to +127; the leftmost bit is the sign bit (0 = positive, 1 = negative).

Binary arithmetic rules: 0+0=0, 0+1=1, 1+1=10 (carry 1), 1+1+1=11; subtraction is done by adding the 2's complement of the subtrahend.

BCD encodes each decimal digit in 4 bits; n bits give 2ⁿ distinct codes, so k bits can represent 2ᵏ values.

Basic gates: AND (Y = A·B, output 1 only if all inputs 1), OR (Y = A+B, output 1 if any input 1), NOT (Y = A′, inverter).

Universal gates: NAND and NOR can each implement AND, OR, and NOT alone, so any circuit can be built from either one.

XOR: Y = A⊕B is 1 when inputs differ; XNOR is its complement and is 1 when inputs are equal.

Boolean identities: A+0=A, A·1=A, A+1=1, A·0=0, A+A=A, A·A=A, A+A′=1, A·A′=0, (A′)′=A.

De Morgan's theorems: (A+B)′ = A′·B′, and (A·B)′ = A′+B′; used to convert between AND/OR forms.

Distributive and absorption laws: A·(B+C) = A·B + A·C; A + A·B = A; A·(A+B) = A.

Truth table rows = 2ⁿ for n input variables; a canonical SOP term (minterm) is 1 for exactly one input combination.

K-map grouping: group 1s in sizes 1, 2, 4, 8, … in powers of two, groups may wrap around edges, and each group must be as large as possible.

Combinational circuits (adders, multiplexers, decoders) depend only on present inputs; sequential circuits (flip-flops, counters, registers) also depend on stored state.

Program development cycle: problem definition → algorithm/flowchart → coding → compilation/interpretation → testing and debugging → documentation and maintenance.

Algorithm properties: finite (terminates), definite (each step unambiguous), has input/output, and is effective; a flowchart draws it with standard symbols.

Flowchart symbols: oval = start/stop, parallelogram = input/output, rectangle = process, diamond = decision, arrow = flow direction.

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

Variable = named memory location holding a value that can change; constant keeps a fixed value; identifier rules usually forbid starting with a digit or using reserved words.

Data types: integer, float/real, character, string, boolean; type conversion may be implicit (coercion) or explicit (casting).

Operators: arithmetic (+, −, *, /, %), relational (<, >, ==, !=), logical (AND, OR, NOT), assignment (=); precedence runs arithmetic → relational → logical.

Array: a collection of same-type elements stored in contiguous locations and accessed by index, usually starting at 0.

Function/procedure: a named reusable block with parameters and a return value (function) or none (procedure); local variables exist only inside it.

DBMS = software that stores, retrieves, and manages data while controlling redundancy, consistency, security, and concurrent access.

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

Keys: 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 minimal unique key.

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

SELECT syntax: 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.

Joins: INNER JOIN returns matching rows only; LEFT/RIGHT OUTER JOIN keeps unmatched rows from one side with NULLs.

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

Data communication has five components: sender, receiver, medium, message, and protocol; transmission modes are simplex, half-duplex, and full-duplex.

Topologies: bus (one backbone), star (central hub/switch), ring (closed loop), mesh (every node linked, most reliable, most cabling), tree/hybrid.

OSI has 7 layers (Physical, Data Link, Network, Transport, Session, Presentation, Application); TCP/IP has 4 (Network Access, Internet, Transport, Application).

LAN covers a building or campus, MAN a city, WAN a country or globe; the Internet is the largest WAN.

IP address identifies a host on a network; IPv4 is 32-bit dotted decimal, IPv6 is 128-bit hexadecimal; a subnet mask separates network and host bits.

MAC address is a 48-bit hardware address burned into the NIC; switches forward frames by MAC, routers forward packets by IP.

Protocols: TCP (connection-oriented, reliable), UDP (connectionless, fast), HTTP/HTTPS (web), FTP (file transfer), SMTP/POP3/IMAP (mail), DNS (name to IP).

Transmission media: guided (twisted pair, coaxial, fiber optic) and unguided (radio, microwave, infrared); fiber carries the highest bandwidth and is immune to EMI.

Bandwidth is capacity in bits per second; latency is delay; a hub broadcasts to all ports, a switch sends only to the destination port.

Internet vs WWW: the Internet is the global network of networks; the World Wide Web is a service of hyperlinked documents accessed over it via HTTP/HTTPS.

URL parts: protocol://domain-or-host:port/path/filename?query#fragment; the domain name is resolved to an IP address by DNS.

HTTP methods: GET requests data (parameters in URL), POST sends data in the body; HTTPS adds TLS encryption.

HTML structure: , , (title, meta), (visible content); tags usually come in opening/closing pairs.

Common HTML elements:

paragraph, link, image,

/
/
1. lists, //

   tables, input.

CSS (inline, internal

JavaScript adds client-side behaviour and validation; it runs in the browser, while server-side code runs on the web server.

Static pages return the same content for every request; dynamic pages generate content per request from a database or script.

A web browser requests a page, the server responds with status codes (200 OK, 404 Not Found, 500 Server Error), and the browser renders the HTML.

Word processor: character/paragraph formatting, styles, tables, spell check, find-and-replace, mail merge, headers/footers, and page setup.

Spreadsheet: cell reference (relative A1, absolute $A$1, mixed $A1/A$1); a formula starts with = and recalculates when referenced cells change.

Spreadsheet functions: SUM, AVERAGE, COUNT, MAX, MIN, IF(condition, value_if_true, value_if_false), and chart types (column, pie, line, scatter).

Presentation software: slide master for consistent design, slide transitions (between slides) vs animations (within a slide), speaker notes, slide sorter.

Multimedia = text + graphics + audio + video + animation; bitmap images store pixels and lose quality when enlarged, vector images store shapes and scale cleanly.

Image resolution is measured in pixels (e.g., 1920×1080); colour depth is bits per pixel; file size ≈ width × height × colour depth / 8 bytes (before compression).

Compression: lossless (PNG, ZIP, FLAC) keeps all data; lossy (JPEG, MP3, MP4) discards detail to shrink files.

Frame rate is frames per second (fps); higher fps gives smoother motion; common video standards are 24, 25, and 30 fps.

E-governance, e-commerce, e-learning, and e-banking are typical application areas of office and internet tools.

CIA triad: Confidentiality (only authorised access), Integrity (data not altered), Availability (accessible when needed).

Malware types: virus (attaches to files), worm (self-replicates across networks), trojan (disguised as useful software), ransomware (encrypts data for payment), spyware (secretly collects data).

Phishing is a fraudulent message that impersonates a trusted party to steal credentials; never share passwords or OTPs, and check the URL before logging in.

Strong password practice: long, mixed case, digits, symbols, unique per site; enable two-factor authentication; avoid personal details and dictionary words.

Firewall filters network traffic by rules; antivirus scans for known malware signatures; encryption converts plaintext to ciphertext using a key.

Digital signature provides authentication, integrity, and non-repudiation; a digital certificate binds a public key to an identity via a CA.

Cyber offences under Indian law (IT Act, 2000): identity theft, phishing, hacking, publishing obscene material, and unauthorised access are punishable.

Cyber ethics: no plagiarism, respect copyright and software licences, no unauthorised access, no cyberbullying, and report incidents to the appropriate authority.

Data backup follows the 3-2-1 rule: 3 copies, on 2 different media, with 1 off-site; a firewall alone does not stop a user from clicking a malicious link.

Cloud computing service models: IaaS (infrastructure), PaaS (platform), SaaS (software); deployment models are public, private, and hybrid.

IoT = network of physical devices with sensors and actuators that collect and exchange data; examples are smart homes, smart meters, and wearable health monitors.

AI/ML: AI builds systems that perform tasks needing human intelligence; machine learning learns patterns from data instead of explicit rules.

Big Data is characterised by volume, velocity, variety, veracity, and value; it is processed with distributed tools rather than a single machine.

Blockchain is a distributed, append-only ledger of linked blocks secured by hashes and consensus; it underlies cryptocurrencies and tamper-evident records.

5G offers higher bandwidth and lower latency than 4G, enabling remote surgery, autonomous vehicles, and dense IoT deployments.

AR overlays digital content on the real world; VR replaces the view with a simulated environment; both are used in training and education.

3D printing (additive manufacturing) builds objects layer by layer from a digital model; GIS links data to geographic locations for mapping and planning.

Vocational applications: computer hardware servicing, DTP, web design, data entry, accounting (Tally), CAD, and IT-enabled services such as call centres and e-commerce operations.