BCS Written ICT flashcards

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

Two's complement range

For an n-bit signed integer, representable values run from -2^(n-1) to 2^(n-1)-1; negation is performed by inverting all bits and adding one.

Universal logic gates

NAND and NOR are called universal because either gate alone can be wired to implement AND, OR and NOT, and therefore any Boolean function.

Von Neumann bottleneck

In a stored-program machine, instructions and data share one memory and bus, so fetching each instruction competes with data access and limits throughput.

Cache memory purpose

Small, fast memory between CPU and RAM that holds recently or frequently used data, reducing average access latency and exploiting temporal and spatial locality.

Thrashing in virtual memory

A condition where excessive page faults force continuous swapping, so the CPU spends most time paging and useful throughput collapses despite high multiprogramming.

Deadlock Coffman conditions

Deadlock requires mutual exclusion, hold and wait, no preemption and circular wait simultaneously; removing any one condition makes deadlock impossible.

Round Robin scheduling

Preemptive scheduling that gives each ready process a fixed time quantum in cyclic order, bounding response time and favoring interactive workloads over minimum average waiting time.

Compiler versus interpreter

A compiler translates the whole source program to object code before execution; an interpreter executes source statements one at a time without producing a separate executable.

OSI seven layers

Physical, Data Link, Network, Transport, Session, Presentation and Application, from hardware transmission upward; TCP/IP collapses the top three into one application layer.

Subnet host count

For a subnet with h host bits, usable addresses equal 2^h - 2, because the all-zeros network address and all-ones broadcast address are reserved.

TCP versus UDP

TCP is connection-oriented with acknowledgments, sequencing and retransmission; UDP is connectionless, has no delivery guarantee, and suits streaming and DNS queries.

Shannon capacity formula

For a noisy channel of bandwidth B hertz and signal-to-noise ratio S/N, maximum capacity in bits per second is B times log base 2 of (1 + S/N).

ARP and DNS roles

ARP resolves an IP address to a MAC address inside a local network; DNS resolves human-readable domain names to IP addresses across the Internet.

ACID properties

Atomicity, Consistency, Isolation and Durability: a transaction completes entirely or not at all, preserves constraints, does not interfere with others, and persists once committed.

Third normal form

A relation is in 3NF when it is in 2NF and no non-key attribute depends transitively on the primary key through another non-key attribute.

Primary versus foreign key

A primary key uniquely and non-nullably identifies each row; a foreign key holds a value matching a candidate key in another relation to enforce referential integrity.

WHERE versus HAVING

WHERE filters individual rows before grouping; HAVING filters groups after GROUP BY and typically tests aggregate results such as COUNT or SUM.

Big-O notation meaning

Big-O describes an upper bound on how an algorithm's resource use grows with input size, ignoring constant factors and lower-order terms.

Stack versus queue

A stack removes the most recently added item (LIFO), used in recursion and expression evaluation; a queue removes the oldest (FIFO), used in scheduling and buffering.

Binary search precondition

Binary search works only on sorted, randomly accessible data; it halves the search interval each step, giving O(log n) time.

BFS versus DFS

Breadth-first search explores level by level with a queue and finds shortest unweighted paths; depth-first search goes deep with a stack and suits cycle detection.

Coupling and cohesion

Coupling measures interdependence between modules and should be low; cohesion measures relatedness within a module and should be high for maintainable design.

DFD balancing rule

In levelled data flow diagrams, the inputs and outputs of a parent process must match exactly those of its child diagram, preserving data conservation.

Black-box testing

Testing derived from specifications without knowledge of internal code, using techniques such as equivalence partitioning, boundary value analysis and decision tables.

Waterfall versus Agile

Waterfall completes sequential phases with frozen requirements before coding; Agile delivers small increments in short iterations with continuous customer feedback.

Digital signature guarantee

Signing with the sender's private key and verifying with the public key proves origin, detects alteration and supports non-repudiation, but does not by itself hide content.

Symmetric versus asymmetric

Symmetric encryption uses one shared secret key and is fast; asymmetric encryption uses a public-private key pair and solves key distribution and signature needs.

SQL injection defense

Attackers insert SQL through unsanitized input; defenses are parameterized queries or prepared statements, input validation, least-privilege database accounts and stored procedures.

HTTP status classes

First digit gives the class: 2xx success, 3xx redirection, 4xx client error, 5xx server error; for example 404 is not found and 500 is server failure.

Cookies versus sessions

Cookies are small client-stored key-value records sent with requests; sessions keep state on the server and identify the client by a session identifier, often in a cookie.

Cloud service models

IaaS supplies virtualized compute and storage, PaaS supplies a managed runtime and middleware, and SaaS supplies complete applications over the network.

Earned value indices

Cost performance index equals earned value divided by actual cost; schedule performance index equals earned value divided by planned value; below one signals overrun or delay.