MATSEC IM Computing flashcards

34 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 the instruction at the address in the program counter, decodes its operation, executes it, and stores the result, then increments the program counter.

Two's complement

A binary representation of signed integers where the leftmost bit is the sign; to negate a value, invert all bits and add one. Eight bits span -128 to +127.

Volatile memory

Memory that loses its stored contents when power is removed. Main memory (RAM) is volatile, whereas ROM and flash storage retain data without power.

Address bus width

The number of address lines determines how many distinct memory locations the CPU can address: n lines allow 2^n locations, so 32 lines address 4 GiB of byte-addressable memory.

XOR gate

A logic gate whose output is 1 when an odd number of its inputs are 1 and 0 otherwise. With two inputs it outputs 1 only when the inputs differ.

Lossless compression

A compression method that reconstructs the original data exactly by encoding redundancy, as used by ZIP, PNG and FLAC, unlike lossy methods that discard detail permanently.

Interrupt

A signal that suspends the currently executing process so the CPU can service a device request or error condition, after which the interrupted process resumes.

Cache memory

A small, fast memory between the CPU and main memory holding recently used instructions and data. It speeds execution by exploiting locality of reference.

Big-O notation

A notation describing an upper bound on how an algorithm's running time or space grows with input size, ignoring constants, for example O(n) for linear search.

Binary search precondition

Binary search requires the data to be sorted. It compares the target with the middle element and discards the half that cannot contain it, halving the search space each step.

Base case

The condition in a recursive algorithm that stops further recursive calls and returns a value directly, preventing infinite recursion and eventual stack overflow.

Stack data structure

A last-in-first-out structure where insertion (push) and removal (pop) occur at the same end, the top, used for expression evaluation and subroutine return addresses.

Queue data structure

A first-in-first-out structure where elements are added at the rear (enqueue) and removed from the front (dequeue), used for scheduling and buffering.

Pass by reference

A parameter-passing mechanism where the function receives the address of the caller's variable, so modifications inside the function change the original argument.

Trace table

A manual table recording each variable's value after every statement or loop iteration, used to check an algorithm's logic and detect off-by-one or assignment errors.

Compiler versus interpreter

A compiler translates the whole source program into object code before execution; an interpreter translates and executes statements one at a time, so errors surface during execution.

Merge sort complexity

Merge sort repeatedly divides the list in half and merges sorted halves, giving O(n log n) time in all cases but requiring O(n) extra memory for merging.

Primary key

A column or minimal set of columns whose values uniquely identify each row in a table. It cannot contain duplicate or null values.

Foreign key

A column in one table that references the primary key of another table, enforcing referential integrity so that no orphan records can exist.

Third normal form

A relation in second normal form with no transitive dependencies, meaning every non-key attribute depends only on the primary key and not on another non-key attribute.

WHERE versus HAVING

WHERE filters individual rows before grouping and cannot contain aggregate functions; HAVING filters groups after GROUP BY and may test aggregate results such as COUNT or SUM.

NULL comparison

NULL represents an unknown value, so testing it with = or <> never returns true. Use IS NULL or IS NOT NULL, and note that COUNT(column) ignores nulls.

ACID properties

Four transaction guarantees: Atomicity (all or nothing), Consistency (valid state to valid state), Isolation (concurrent transactions do not interfere) and Durability (committed changes persist).

Validation versus verification

Validation checks data is reasonable and within rules such as range or format; verification checks data was entered or transferred accurately, for example by double entry.

Incremental backup

A backup that copies only data changed since the most recent backup of any type. It is fast and small but restoration requires the last full backup plus every increment.

Sequential file access

A file organisation where records are read in stored order from the beginning. It suits batch processing but is slow for locating a single record.

Data minimisation

A data protection principle requiring that only personal data adequate, relevant and necessary for the stated purpose is collected and retained, and no more.

Unauthorised access offence

Computer misuse legislation makes it an offence to cause a computer to perform a function to gain access to programs or data without authorisation, with higher penalties if further offences are intended.

Open source licence

A software licence that makes the source code available for inspection, modification and redistribution, often requiring derivative works to carry the same licence terms.

Waterfall model

A sequential development life cycle where each stage (requirements, design, implementation, testing, maintenance) completes before the next begins, suiting stable, well-understood requirements.

Acceptance testing

Testing in which the intended users check the completed system against their requirements and business needs, providing formal sign-off before the system goes live.

Economic feasibility

An assessment of whether the benefits of a proposed system justify its development and running costs, often judged using cost-benefit analysis and payback period.

Digital divide

The unequal access to devices, internet connectivity and digital skills among groups, which affects participation in education, employment and public services.

White-box testing

Testing that uses knowledge of the program's internal structure to exercise specific code paths, branches and conditions, complementing black-box testing of external behaviour.