BSEH SS Computer Science key terms

The main chip that fetches, decodes and executes program instructions. It contains the control unit, which directs operations, and the arithmetic logic unit, which performs calculations and comparisons.

The part of the processor that carries out arithmetic operations such as addition and subtraction and logical operations such as AND, OR and comparisons of two values.

Volatile working storage that holds the instructions and data currently in use. Its contents are lost when power is switched off, so programs must be reloaded each session.

Non-volatile media such as hard disks, solid-state drives and pen drives that keep data permanently when power is removed. It is slower than RAM but far larger in capacity.

A small, very fast memory between the processor and RAM that keeps recently used instructions and data, reducing the average time the CPU waits for information from main memory.

Hardware that carries data into a computer (keyboard, mouse, scanner, microphone) or sends results out of it (monitor, printer, speaker). Some devices, such as touchscreens, do both.

A base-2 system that uses only the digits 0 and 1, each position representing a power of two. Computers use it because a circuit can easily represent two states, on and off.

A base-16 system using digits 0-9 and letters A-F. Each hex digit maps exactly to four binary bits, so it is used as a compact way to write memory addresses, colours and byte values.

A bit is a single binary digit, 0 or 1. A byte is a group of eight bits and is the standard unit for storing one character; larger units are kilobyte, megabyte, gigabyte and terabyte.

A rule that assigns a numeric code to each character so text can be stored as binary. ASCII covers 128 English characters; Unicode covers characters of most of the world's writing systems.

A method of representing signed integers in binary in which the leftmost bit gives the sign. Negating a value means inverting all bits and adding one, which makes subtraction work as addition.

System software that manages hardware, memory, files and processes, and provides services that application programs use. Examples include Windows, Linux, macOS and Android.

The part of an operating system that organises data on storage into files and directories, and records names, sizes, locations and permissions. Examples are NTFS, FAT32 and ext4.

An absolute path states a file's full location from the root, such as /home/rita/notes.txt. A relative path starts from the current working directory, such as notes.txt or ../data/report.csv.

A program in execution, with its own memory space, program counter and state (running, waiting, ready). The operating system schedules processes so several can share one processor.

A finite, ordered set of unambiguous steps that solves a problem or produces a result. A good algorithm is correct, terminates and uses reasonable time and memory.

A diagram of an algorithm using standard symbols: oval for start and stop, parallelogram for input and output, rectangle for processing, diamond for decisions and arrows for the order of steps.

A structured, English-like description of an algorithm that avoids the syntax of any particular language. It uses keywords such as INPUT, IF, WHILE and END to show logic clearly.

A variable is a named storage location whose value can change while a program runs. Its data type, such as int, float, str or bool, decides which values it may hold and which operations apply.

The three ways statements are combined: sequence runs them in order, selection chooses a path with if or else, and iteration repeats them with for or while loops.

A statement that runs one block of code when a condition is true and another block otherwise. In Python, indentation, not braces, marks which statements belong to each block.

A construct that repeats a block of code. A for loop iterates over a sequence or a range of numbers; a while loop repeats as long as a condition stays true.

A named block of code that performs a task and can be called repeatedly. Parameters are the names in its definition that receive the arguments supplied in each call; return sends a value back.

Changing a value from one data type to another, as in int("42") or str(7). Explicit conversion uses functions; implicit conversion happens automatically when Python combines compatible types such as int and float.

An ordered, mutable collection written in square brackets, such as [3, 1, 4]. Items are accessed by index starting at 0 and can be added, changed or removed after creation.

An index selects one element by position, counting from 0; negative indexes count from the end. A slice such as a[1:4] returns a new sequence from the start index up to, but not including, the end index.

A collection in which the last item added is the first removed, like a pile of plates. The main operations are push to add on top, pop to remove the top item and peek to view it.

A collection in which the first item added is the first removed, like a line at a ticket counter. Enqueue adds at the rear, dequeue removes from the front, and both ends are tracked.

Visiting each element of a list in turn, usually with a for loop such as for item in marks. It is the standard way to total, search or transform every item in a sequence.

A column, or combination of columns, whose value uniquely identifies each row of a table. It cannot be null and no two rows may share the same key value.

A column in one table that refers to the primary key of another table, linking the two rows. It enforces referential integrity by rejecting values that match no parent row.

The query command that retrieves rows from tables. Its clauses are SELECT for columns, FROM for tables, WHERE for row conditions, GROUP BY for grouping and ORDER BY for sorting the result.

An IP address is the numeric label that identifies a device on a network. DNS is the service that translates a readable domain name such as example.com into its IP address.

An agreed set of rules for exchanging data. TCP/IP governs addressing and reliable delivery of packets across the internet; HTTP defines how browsers request and receive web pages.

A LAN connects devices within a small area such as a school or office. A WAN links networks across large distances; the internet is the largest WAN, joining many smaller networks.

A tag is markup written in angle brackets, such as

. An element is the whole unit from opening tag to closing tag, including its content, for example

Hello

.

The standard skeleton of a page: a doctype declaration, then head for metadata and title, then body for visible content. Browsers use this structure to render the page correctly.

A clickable link created with the a element and its href attribute, pointing to another page, a file or a section of the same page. It is the basis of navigation on the web.

The address of a resource on the web. It combines a scheme such as https, a domain name, an optional path and file name, and sometimes a query string.

A strong password is long and mixes character types so it resists guessing. Two-factor authentication adds a second proof, such as a one-time code, so a stolen password alone is not enough.

A trick in which a message imitates a trusted person or organisation to make the recipient reveal passwords, card details or money. Suspicious links and urgent wording are warning signs.

Software written to harm or exploit a system, including viruses, worms, trojans and ransomware. Protection comes from updated antivirus software, patched systems and caution with unknown downloads.

AI is the field of building systems that perform tasks needing human-like judgement. Machine learning is one approach in which a program learns patterns from data instead of following only hand-written rules.

Testing runs a program with chosen inputs to find errors; debugging locates and fixes them. Print statements, breakpoints and checking boundary cases are common practical techniques.

Written material that explains what a program does, how to run it and how it was built. A report typically covers aim, design, code listing, test results, limitations and possible improvements.