NSSCAS Computer Science (8231) flashcards

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

Two's complement

A signed binary representation in which the most significant bit has negative place value; negative x is formed by inverting all bits of x and adding one.

Hexadecimal

A base-16 number system using digits 0-9 and A-F; one hexadecimal digit represents four binary bits and is often used for memory addresses and colour codes.

Lossless compression

A reversible compression method that reduces file size without discarding any original data, often using run-length encoding or Huffman coding.

Bitmap file size

For an uncompressed bitmap, file size in bits equals width in pixels multiplied by height in pixels multiplied by colour depth in bits per pixel, plus header overhead.

TCP versus UDP

TCP is connection-oriented, reliable, ordered and retransmits lost segments; UDP is connectionless with no delivery guarantee, lower overhead and suits streaming or DNS queries.

Subnet mask

A 32-bit IPv4 value that separates the network portion from the host portion of an address; a 1 bit marks network bits and 0 marks host bits.

Packet switching

Data is split into packets with headers containing destination and sequence information; packets may take different routes and are reassembled at the destination.

Von Neumann architecture

A computer design in which instructions and data share the same memory and are transferred to the CPU over common buses, creating a potential bottleneck.

Fetch-decode-execute cycle

The CPU cycle that fetches an instruction using the program counter, decodes its operation, executes it, and then updates the program counter for the next instruction.

Cache memory

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

Compiler

System software that translates the whole source program into object code before execution, reporting syntax errors and producing an executable file.

Paging

A memory-management technique dividing physical memory into fixed-size frames and logical memory into pages, with a page table mapping pages to frames.

Device driver

System software that translates general operating-system commands into device-specific instructions so a particular hardware device can be controlled.

Symmetric encryption

An encryption method using the same secret key for both encryption and decryption; it is fast but the key must be distributed securely.

Digital signature

A value created by encrypting a hash of a message with the sender's private key; the receiver verifies it with the sender's public key.

Data validation

Automated checks on input such as range, type, length, presence and format that reject data failing predefined rules before it is processed or stored.

Copyright

A legal right protecting original expression such as text, music, code or images; it does not protect the underlying idea itself.

Computer misuse legislation

Laws that criminalise unauthorised access to computer systems, unauthorised modification of data, and using a computer to commit further offences; exact names vary by country.

Algorithmic bias

Systematic unfairness in automated decisions caused by biased or unrepresentative training data, flawed objectives, or biased design choices; mitigation includes audit and diverse data.

Primary key

A field or combination of fields that uniquely identifies each record in a relational 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 between related records.

Third normal form

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

SQL INNER JOIN

A query operation returning only rows where the join condition matches in both tables; unmatched rows from either table are excluded from the result.

Binary search

A search on sorted data that compares the target with the middle item and repeatedly halves the remaining interval, running in O(log n) time.

Stack

A last-in-first-out data structure supporting push and pop operations; the most recently added item is removed first.

Big-O notation

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

Pass by reference

A parameter-passing method where the procedure receives the address of the argument, so changes to the parameter affect the caller's original variable.

Record data structure

A composite data type grouping named fields that may have different data types, representing one logical entity such as a student.

Array bounds checking

A runtime or compile-time check that an index lies within the valid range of an array, preventing access outside allocated memory.

Waterfall model

A sequential software development model progressing through requirements, design, implementation, testing and maintenance, with limited backtracking between stages.

Black-box testing

Testing that exercises software through its inputs and outputs without examining internal code structure, often based on the specification.

Regression testing

Re-running previously passed tests after changes to confirm that new code has not broken existing functionality.