Punjab PSEB SS Computer Science flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Binary number system

A base-2 positional number system that uses only the digits 0 and 1. Each position represents a power of 2, so 1011 in binary equals 11 in decimal.

Hexadecimal system

A base-16 number system using digits 0-9 and letters A-F. Each hex digit represents exactly four binary bits, which makes it a compact shorthand for binary values.

Bit and byte

A bit is a single binary digit, 0 or 1. A byte is a group of 8 bits and can represent 256 different values, enough for one ASCII character.

Two's complement

A method of representing signed integers in binary. To negate a number, invert all its bits and add 1. In 8 bits, the range is -128 to +127.

NAND gate

A logic gate whose output is the inverse of AND: it gives 0 only when all inputs are 1, otherwise 1. It is a universal gate because any circuit can be built from NAND gates alone.

XOR gate

A logic gate that outputs 1 when its two inputs are different and 0 when they are the same. It is used to build adders and parity checkers.

Half adder

A combinational circuit that adds two single bits. It produces Sum = A XOR B and Carry = A AND B, but it cannot accept a carry from a previous stage.

Truth table

A table listing every possible combination of input values for a logic circuit and the resulting output. A circuit with n inputs has 2^n rows.

RAM vs ROM

RAM is read-write memory that loses its contents when power is switched off (volatile). ROM is read-only and retains its contents permanently (non-volatile), holding startup instructions.

Cache memory

A small, very fast memory placed between the CPU and main memory. It stores recently used instructions and data to reduce average access time.

Compiler vs interpreter

A compiler translates the whole program into machine code before execution, producing a file. An interpreter translates and runs line by line, so errors stop execution immediately.

Operating system

System software that manages hardware, processes, memory, files and input/output devices, and provides a user interface. Windows, Linux and Android are examples.

Algorithm

A finite, ordered set of unambiguous steps that solves a problem and terminates. It must accept input, produce output, and be definite, effective and finite.

Flowchart symbols

Oval for start/stop, parallelogram for input/output, rectangle for a process, diamond for a decision, and arrow for control flow. They diagram an algorithm before coding.

Local vs global variable

A local variable is declared inside a block or function and is visible only there. A global variable is declared outside and is accessible throughout the program.

While vs do-while loop

A while loop tests its condition before each iteration, so the body may never run. A do-while tests after the body, so the body runs at least once.

Array

A collection of elements of the same data type stored in consecutive memory locations and accessed by an index. In most languages the first index is 0.

Binary search

A search algorithm that repeatedly halves a sorted array, comparing the target with the middle element. It runs in O(log n) time but needs sorted data.

Bubble sort

A sorting algorithm that repeatedly compares adjacent elements and swaps them when out of order. After each pass the largest remaining element reaches its final position.

Primary key

A field (or set of fields) in a database table whose value uniquely identifies each row. It cannot contain duplicate or null values.

Foreign key

A field in one table that refers to the primary key of another table. It enforces referential integrity and links related records across tables.

DBMS

Database Management System: software that stores, retrieves, updates and secures data in a database, and controls concurrent access. MySQL and Oracle are examples.

LAN

Local Area Network: a network covering a limited area such as a room, building or campus, usually owned by one organisation and offering high data rates.

WAN

Wide Area Network: a network spanning a large geographical area such as a country or the globe, often linking LANs through public or leased telecommunication lines. The Internet is the largest WAN.

IP address

A unique numeric address that identifies a device on a network. IPv4 uses 32 bits written as four dotted decimal numbers, such as 192.168.1.1.

DNS

Domain Name System: a distributed naming service that translates human-readable domain names, such as example.com, into the numeric IP addresses computers use to route traffic.

TCP vs UDP

TCP is connection-oriented: it establishes a session, acknowledges data and retransmits lost packets. UDP is connectionless, faster but unreliable, and suits streaming and gaming.

HTTP and HTTPS

HTTP is the protocol browsers use to request web pages. HTTPS is HTTP carried over an encrypted TLS connection, protecting data such as passwords and card details.

Phishing

A fraudulent email, message or website that impersonates a trusted source to trick a user into revealing passwords, card numbers or other sensitive information.

Computer virus

Malicious code that attaches itself to a legitimate program or file and spreads when that file is executed. It can corrupt data and slow the system.

Firewall

Hardware or software that monitors incoming and outgoing network traffic and blocks packets that violate configured security rules, protecting a computer or network from unauthorised access.

Strong password

A password long enough and mixed in character types (upper and lower case, digits, symbols) that guessing is impractical. It should be unique per account and never shared.