NSSCO Computer Studies (6134) flashcards

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

Von Neumann architecture

Design in which CPU and memory share a single bus for both instructions and data, with the program stored in memory alongside the data it processes.

Fetch-decode-execute cycle

Repeating process where the CPU fetches an instruction from the address in the program counter, decodes its operation, then executes it before moving to the next.

Cache memory

Small, fast memory between the CPU and RAM that stores recently or frequently used instructions and data, exploiting locality of reference to reduce average access time.

Compiler versus interpreter

A compiler translates the whole source program into object code before running it; an interpreter translates and executes one statement at a time, easing debugging but slowing execution.

Two's complement range

For an n-bit signed integer, representable values run from -2^(n-1) up to 2^(n-1) - 1; negate a value by inverting all bits and adding one.

Hexadecimal to binary conversion

Each hexadecimal digit maps to exactly four binary bits, so converting AF gives 1010 1111; one byte is always written as two hexadecimal digits.

Overflow in binary addition

Condition where a result exceeds the range of the register, detected when a carry into the sign bit differs from the carry out of it.

Lossy versus lossless compression

Lossy compression permanently discards data for smaller files (JPEG, MP3); lossless compression encodes patterns so the exact original can be rebuilt (PNG, FLAC, ZIP).

Image file size formula

File size in bits equals width in pixels multiplied by height in pixels multiplied by colour depth in bits per pixel; divide by eight for bytes.

Unicode compared with ASCII

ASCII encodes 128 characters in seven bits; Unicode uses variable encodings such as UTF-8 and UTF-16 to represent characters from all writing systems.

TCP versus UDP

TCP is connection-oriented, orders segments and retransmits lost ones, suitable for file transfer; UDP is connectionless with no delivery guarantee, suitable for streaming and voice.

DNS purpose

The Domain Name System translates human-readable domain names into numeric IP addresses so browsers can locate the correct server on the Internet.

Router versus switch

A router forwards packets between different networks using IP addresses; a switch forwards frames within one local network using MAC addresses.

OSI model layers

Seven layers from lowest: Physical, Data Link, Network, Transport, Session, Presentation and Application, each providing defined services to the layer above.

DHCP function

Dynamic Host Configuration Protocol automatically supplies a device joining a network with an IP address, subnet mask, default gateway and DNS server addresses.

Primary key

A field or combination of fields that uniquely identifies each record in a table and cannot contain duplicate or null values.

Foreign key

A field in one table that references the primary key of another table, enforcing referential integrity by preventing records that point to nonexistent entries.

Third normal form

A table is in 3NF when it is in 2NF and contains no transitive dependencies, meaning non-key fields depend only on the primary key.

Data validation versus verification

Validation checks input against rules such as range or type; verification confirms the data accurately matches the original source, for example by double entry.

SELECT statement

SQL command that retrieves specified columns from one or more tables, optionally filtered by a WHERE condition and ordered with ORDER BY.

Binary search precondition

Binary search requires the data to be sorted; it repeatedly halves the search interval by comparing the middle element with the target.

Logic error

A fault in the algorithm or program design that allows the program to run but produce incorrect output, unlike syntax errors that stop translation.

Count-controlled loop

An iteration structure such as FOR that repeats a known number of times, using a counter initialised before the loop and incremented each pass.

Procedure versus function

A procedure performs an action and may return no value; a function performs a calculation and returns exactly one value to the calling statement.

Trace table purpose

A manual record of variable values after each program statement, used to dry-run an algorithm and locate logic errors such as off-by-one mistakes.

Truth table rows

For a Boolean expression with n input variables, the truth table has 2^n rows, listing every combination of true and false inputs with the output.

Phishing

A social engineering attack using fraudulent emails or websites that impersonate trusted organisations to trick users into revealing passwords or financial details.

Ransomware

Malicious software that encrypts a victim's files or locks the system, then demands payment for the decryption key needed to restore access.

Cloud computing service models

IaaS supplies virtual hardware, PaaS supplies a development platform, and SaaS supplies ready-to-use applications, all delivered over the Internet on demand.

Digital divide

The gap between people who have affordable access to devices, connectivity and digital skills and those who are excluded from these opportunities.

Internet of Things

A network of everyday physical devices embedded with sensors and network connectivity that collect and exchange data without direct human intervention.

Computer misuse offence

Unauthorised access to computer material, unauthorised modification of data, or unauthorised access with intent to commit a further crime, punishable under law.