MATSEC SEC Computing 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 repeating CPU cycle: fetch the instruction at the program counter address, decode its opcode, execute it, and store the result. The program counter then advances unless a jump changes it.

Von Neumann architecture

A computer design in which instructions and data share the same memory and bus. This simple design creates the von Neumann bottleneck because only one item can be fetched at a time.

Two's complement

A signed binary representation where negating a value means inverting all bits and adding one. An n-bit signed number ranges from -2^(n-1) to 2^(n-1)-1, and subtraction uses ordinary addition.

Cache memory

Small, fast memory between the CPU and RAM that stores recently or frequently used data. It exploits locality of reference and gives faster access than main memory at higher cost per byte.

RISC versus CISC

RISC uses a small set of fixed-length instructions with many registers and simple addressing. CISC offers complex variable-length instructions. RISC suits pipelining; CISC reduces program size.

Logic gate XOR

An exclusive-OR gate outputs 1 only when its two inputs differ, and 0 when both inputs are the same. It is used in parity checking and binary addition without carry.

Primary versus secondary storage

Primary storage (RAM, ROM) is directly addressable by the CPU and RAM is volatile. Secondary storage (hard disk, SSD, optical) is non-volatile, cheaper per byte and slower, accessed via controllers.

TCP versus UDP

TCP is connection-oriented, sequencing data and retransmitting lost packets to guarantee delivery. UDP is connectionless with no delivery guarantee, giving lower overhead for streaming and real-time traffic.

DNS

The Domain Name System translates human-readable domain names such as example.com into IP addresses. It uses a distributed hierarchy of name servers and normally runs on port 53.

Subnet mask /24

A 24-bit mask (255.255.255.0) where the first 24 bits identify the network and the last 8 bits identify hosts. It allows 254 usable host addresses after excluding network and broadcast.

OSI model layers

Seven layers from the bottom: Physical, Data Link, Network, Transport, Session, Presentation and Application. Each layer provides services to the layer above and communicates with its peer layer.

DHCP

The Dynamic Host Configuration Protocol automatically assigns IP addresses, subnet masks, default gateways and DNS servers to devices joining a network, avoiding manual configuration and address conflicts.

Private IPv4 addresses

Address ranges reserved for internal networks and not routed on the public internet: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. NAT translates them to public addresses.

Star topology

A network layout in which every device connects to a central switch or hub. Failure of one cable affects only that device, but failure of the central device disables the whole network.

HTTPS

HTTP carried over TLS encryption, normally on port 443. It provides confidentiality and integrity plus server authentication through certificates, protecting data such as passwords and payment details.

Binary search complexity

Binary search repeatedly halves a sorted array, so it runs in O(log n) time. It requires random access and sorted data; on an unsorted array the data must be sorted first.

Big-O notation

Notation describing an upper bound on how an algorithm's time or space grows with input size. Common classes in increasing order are O(1), O(log n), O(n), O(n log n), O(n^2).

Stack

A last-in-first-out data structure where push adds to the top and pop removes from the top. Uses include function call management, undo operations and expression evaluation.

Queue

A first-in-first-out data structure where enqueue adds at the rear and dequeue removes from the front. It is used for scheduling, buffering and breadth-first traversal of graphs.

Merge sort

A divide-and-conquer sort that splits the list, sorts each half recursively, then merges them. It runs in O(n log n) time in all cases but needs extra memory for merging.

Hash table

A structure mapping keys to array positions through a hash function, giving average O(1) lookup. Collisions are resolved by chaining or open addressing, which can degrade performance.

Breadth-first search

A graph traversal using a queue that visits all neighbours of a node before going deeper. It finds shortest paths in unweighted graphs and runs in O(V + E) time.

Recursion base case

The condition that stops a recursive function from calling itself again. Without a correct base case, recursion continues until the call stack overflows and the program crashes.

Pass by value versus reference

Pass by value gives the function a copy, so changes do not affect the original variable. Pass by reference passes the address, so the function can modify the caller's variable.

Compiler versus interpreter

A compiler translates the whole source program into machine code before running it. An interpreter translates and executes line by line, which aids debugging but usually runs slower.

Three basic control structures

Sequence executes statements in order; selection chooses a path using if or switch; iteration repeats using for, while or do-while loops. Every algorithm can be built from these.

Validation versus verification

Validation checks that input is sensible and within acceptable rules, such as range or type. Verification checks that data matches its original source, for example by double entry.

Black-box testing

Testing that treats the program as opaque and checks outputs for given inputs against requirements, without examining internal code. It complements white-box testing of code paths.

Primary key

A field or combination of fields that uniquely identifies each record in a table. It cannot be null or duplicated, and other tables reference it through foreign keys.

Third normal form

A table is in 3NF when it is in 2NF and no non-key attribute depends on another non-key attribute. This removes transitive dependencies and reduces update anomalies.

SQL WHERE versus HAVING

WHERE filters individual rows before grouping, while HAVING filters groups after aggregation. HAVING is therefore used with aggregate functions such as COUNT or SUM.

Cloud service models

IaaS supplies virtual machines and storage; PaaS supplies a development and runtime platform; SaaS supplies finished applications over the internet. Responsibility for management shifts from user to provider.