Nepal SEE Computer Science flashcards

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

Binary number system

A base-2 number system using only the digits 0 and 1. Each position represents a power of 2, so 1011 equals 8+0+2+1 = 11 in decimal.

Hexadecimal conversion

Base-16 system using digits 0-9 and letters A-F. Each hex digit equals exactly four binary bits, so 2F equals 0010 1111 in binary and 47 in decimal.

Two's complement

A method of representing negative binary numbers by inverting all bits and adding 1. An 8-bit signed range runs from -128 to +127.

Nibble and byte

A nibble is 4 bits and a byte is 8 bits. One byte can store 256 different values, from 0 to 255 in unsigned form.

Universal gates

NAND and NOR gates are called universal because any other logic gate or circuit can be constructed using only NAND gates or only NOR gates.

XOR gate

The exclusive-OR gate outputs 1 when its inputs differ and 0 when they are the same. It forms the sum output of a half adder.

Half adder

A combinational circuit adding two single bits. Sum equals A XOR B and Carry equals A AND B, giving four truth-table rows.

Truth table rows

A truth table lists every input combination. For n input variables the table has 2^n rows, so three variables produce eight rows.

Volatile memory

RAM is volatile: its contents are lost when power is switched off. ROM is non-volatile and retains data permanently, holding firmware such as the BIOS.

Compiler versus interpreter

A compiler translates the whole source program at once and lists all errors together. An interpreter translates and runs line by line, stopping at the first error.

Control unit

The CPU component that fetches instructions, decodes them and directs other units to execute them. It does not perform arithmetic itself.

Impact printer

A printer that strikes an inked ribbon against paper, such as a dot-matrix or daisy-wheel printer. It is noisy but can print multi-part carbon forms.

Firmware

Software stored permanently in read-only memory, such as the BIOS that starts a computer. It sits between pure hardware and ordinary software.

Network topology

The physical arrangement of nodes in a network. Common types are star with a central switch, ring, bus with a shared backbone, and mesh.

LAN versus WAN

A LAN covers a limited area such as a room or building, while a WAN spans cities or countries. The Internet is the largest example of a WAN.

IPv4 address

A 32-bit logical address written as four decimal octets separated by dots, for example 192.168.1.1. IPv6 uses 128 bits instead.

Usable hosts per subnet

With n host bits, usable addresses equal 2^n minus 2, because the network address and broadcast address cannot be assigned to hosts.

Computer worm

A self-replicating malicious program that spreads across networks without attaching to a host file, often slowing networks by consuming bandwidth.

Phishing

A cyberattack in which a fake message or website tricks a user into revealing passwords or bank details by impersonating a trusted organisation.

SMTP and POP3

SMTP is the protocol for sending outgoing email, while POP3 downloads incoming mail from a server to a local client, usually deleting it from the server.

QBasic CLS statement

The CLS statement clears all text from the screen. It is commonly placed at the start of a program to give a clean output display.

QBasic LEN function

LEN(string) returns the number of characters in a string, including spaces. For example, LEN("Nepal") returns the value 5.

QBasic MOD operator

MOD returns the remainder after integer division. For example, 17 MOD 5 gives 2, while the integer division 17 \ 5 gives 3.

FOR...NEXT loop

A counted loop in QBasic that repeats a block a known number of times, controlled by a start value, end value and optional STEP.

SELECT CASE statement

A QBasic decision structure that compares one expression against several CASE values, replacing long chains of nested IF statements.

HTML anchor tag

The <a> tag creates a hyperlink. Its href attribute holds the destination address, as in <a href="page.html">Next</a>.

HTML image tag

The <img> tag embeds a picture and needs no closing tag. The src attribute gives the file path and alt supplies alternative text.

HTML ordered list

An <ol> element creates a numbered list, and each entry is wrapped in <li> tags. An unordered list uses <ul> for bullets instead.

HTML table cell

The <td> tag defines a data cell inside a <tr> row, while <th> defines a bold centred header cell. Colspan merges cells horizontally.

Primary key

A field that uniquely identifies every record in a table. It can never be empty or duplicated, and it is often an AutoNumber field.

Foreign key

A field in one table that stores the primary key value of another table, creating a relationship and enforcing referential integrity between the tables.

SQL SELECT statement

The statement that retrieves data from a table. SELECT name FROM student WHERE marks > 60 returns only rows meeting the condition.

SQL aggregate functions

COUNT, SUM, AVG, MAX and MIN summarise many rows into one value. COUNT(*) counts all rows, while COUNT(field) ignores null entries.