Praxis Computer Science flashcards

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

Fetch-decode-execute cycle

The CPU repeatedly fetches an instruction from memory, decodes its operation, executes it using the ALU or control unit, and stores any result.

Two's complement range

For an n-bit signed integer, two's complement represents values from negative two to the power n minus one through positive two to the power n minus one minus one.

Cache memory

A small, fast memory between the CPU and main memory that stores recently or frequently used data to reduce average memory access time.

Virtual memory

An operating-system technique that maps logical addresses to physical memory or disk, letting programs use more memory than physically installed.

RISC versus CISC

RISC uses many simple fixed-length instructions executed quickly, while CISC uses fewer complex variable-length instructions; each design trades instruction count against per-instruction complexity.

Amdahl's law

Speedup from improving part of a system is limited by the fraction improved: speedup equals one divided by the sum of unimproved fraction plus improved fraction divided by improvement factor.

Big-O notation

A notation describing an algorithm's upper bound on growth rate as input size increases, ignoring constants and lower-order terms.

Binary search

A search on a sorted array that repeatedly compares the target with the middle element and discards half the remaining elements, running in logarithmic time.

Stack data structure

A last-in, first-out collection where push adds an item to the top and pop removes the most recently added item.

Hash table average lookup

A data structure mapping keys to values through a hash function; with good hashing and low load factor, insertion, deletion, and lookup average constant time.

Breadth-first search

A graph traversal using a queue that visits all neighbors at the current depth before deeper nodes; on unweighted graphs it finds shortest paths in edges.

Recursion base case

A condition that stops a recursive function from calling itself again; without a correct base case, recursion continues until the call stack overflows.

Primary key

A column or set of columns that uniquely identifies each row in a relational table and cannot contain null values.

Foreign key

A column in one table that references the primary key of another table, enforcing referential integrity between related records.

Third normal form

A relation is in 3NF when it is in 2NF and has no transitive dependencies, meaning non-key attributes depend only on candidate keys.

ACID transactions

Database transaction properties: atomicity means all or nothing, consistency preserves constraints, isolation prevents interference, and durability survives failures.

Inverted index

A retrieval structure mapping each term to the list of documents containing it, enabling fast Boolean and ranked keyword searches.

TCP versus UDP

TCP is connection-oriented and reliable with ordered delivery and retransmission; UDP is connectionless and unreliable, favored for low-latency streaming and DNS queries.

DNS resolution

The Domain Name System translates human-readable domain names into IP addresses through a hierarchy of root, top-level, and authoritative name servers.

IPv4 private addresses

Private IPv4 ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16; they are not routed on the public internet and require NAT for external access.

HTTPS

HTTP secured by TLS, typically on port 443, providing encrypted communication, server authentication through certificates, and integrity checking for web traffic.

Subnet mask

A 32-bit mask that separates an IPv4 address into network and host portions; CIDR notation such as /24 indicates the number of leading network bits.

Digital divide

The gap between people who have affordable access to computing devices, internet connectivity, and digital skills and those who do not.

Intellectual property

Legal protections for creations of the mind, including copyright for expressive works, patents for inventions, trademarks for brand identifiers, and trade secrets.

Algorithmic bias

Systematic unfairness in automated decisions caused by biased training data, flawed feature selection, or design choices that disadvantage particular groups.

Open-source license

A license granting users rights to run, study, modify, and redistribute software source code, often requiring derivative works to keep the same license.

E-waste

Discarded electronic equipment containing hazardous materials; responsible recycling recovers valuable metals and prevents soil and water contamination.

CIA triad

The core security model: confidentiality limits unauthorized data access, integrity prevents unauthorized modification, and availability ensures timely reliable access to systems.

Multi-factor authentication

Authentication using two or more independent factors from knowledge, possession, or inherence, reducing risk when one factor such as a password is compromised.

Symmetric encryption

Encryption using the same secret key for both encryption and decryption; fast and suitable for bulk data but requires secure key distribution.

Phishing attack

A social-engineering attack that tricks users into revealing credentials or clicking malicious links by impersonating a trusted entity in messages.

SQL injection

An attack inserting malicious SQL through unvalidated input so the database executes unintended queries; prevention uses parameterized queries and input validation.