IB Computer Science HL key terms

Any person or group affected by a system, such as users, managers, or IT staff. Their requirements are gathered during analysis and shape the design decisions made later.

A documented statement of what a new system must do, covering functional needs and constraints. It is agreed with the client before design starts and is used to judge the finished product.

An early investigation judging whether a proposed system is technically, economically, legally, and operationally workable. Its conclusion decides whether the project proceeds to full analysis and design.

The method used to move from an old system to a new one: direct, parallel, phased, or pilot. Each option trades cost and risk differently when data and users must migrate.

Transferring existing records from an old system into a new one, often requiring cleaning, reformatting, and validation. Poorly planned migration causes lost or corrupted data at changeover.

An older system still in use that may be costly to maintain and hard to integrate with newer technology. Organisations must decide whether to replace, extend, or retire it.

Small, very fast memory between the CPU and main memory holding recently used instructions and data. It reduces average access time because most requests are served without reaching slower RAM.

Memory the CPU addresses directly, namely RAM and ROM. RAM holds programs and data in use and loses contents when power is removed; ROM keeps its contents permanently.

A technique where part of secondary storage acts as an extension of RAM, moving pages between disk and memory. It allows large programs to run but is far slower than real memory.

Overlapping the stages of instruction execution so several instructions are in progress at once. Throughput rises because each stage works on a different instruction simultaneously.

A design in which instructions and data share one memory and travel over a common bus to the CPU. The single bus creates a bottleneck known as the von Neumann bottleneck.

A set of agreed rules governing how devices format, send, and receive data over a network. Without shared protocols, hardware from different vendors could not communicate.

Dividing data into packets that are routed independently across a network and reassembled at the destination. It uses shared links efficiently and can survive partial network failure.

A numeric label identifying a device on a network so data can be routed to it. IPv4 uses 32 bits while IPv6 uses 128 bits, giving a vastly larger address space.

A bit pattern that separates the network portion of an IP address from the host portion. Devices use it to decide whether a destination is local or must be sent to a router.

A finite, ordered set of unambiguous steps that solves a problem or completes a task. Every step must be executable and the process must terminate after a limited number of operations.

A structured, language-independent notation for expressing algorithms using keywords and indentation. It communicates logic to humans without the syntax rules of a real programming language.

A manual record of variable values after each step of an algorithm, used to test logic and find errors. It shows exactly where behaviour diverges from what was intended.

Working through an algorithm by hand with sample input, recording each change of state. It verifies logic before code is written and exposes errors such as infinite loops.

A technique where a method calls itself on a smaller version of the same problem until a base case is reached. Each call uses stack space, so deep recursion risks overflow.

The condition in a recursive method that returns a result without calling itself again. Without a correct base case, recursion continues until the call stack overflows.

A last-in-first-out structure where items are pushed and popped at one end only. It supports undo operations, expression evaluation, and the call management of recursive methods.

A first-in-first-out structure where items are added at the rear and removed from the front. It models fair waiting lines and buffers data between processes running at different speeds.

A collection of nodes, each holding data and a reference to the next node. Insertion and deletion are cheap once a position is found, but access is sequential.

A variable that stores the memory address of another item rather than the data itself. Pointers link nodes in dynamic structures and allow efficient sharing without copying.

A binary tree where every left descendant is smaller and every right descendant larger than its parent. Searching is fast when balanced but degrades to a list when unbalanced.

A systematic method of visiting every node in a tree, such as in-order, pre-order, or post-order. In-order traversal of a binary search tree outputs values in sorted order.

A calculation that converts a key into an index within a fixed range of storage locations. A good function spreads keys evenly, keeping collisions and search time low.

The strategy used when two keys hash to the same location, typically open addressing or chaining. The choice affects performance as the table fills up.

Software that manages hardware, memory, files, and processes and provides services to applications. It schedules the CPU, handles interrupts, and enforces access rights between users.

The operating system policy deciding which ready process receives the CPU next, for example round robin or priority. It balances throughput, response time, and fairness.

A situation where processes each hold a resource and wait for one held by another, so none can proceed. It requires mutual exclusion, hold-and-wait, no preemption, and circular wait.

An integer variable with atomic wait and signal operations that controls access to shared resources. It can enforce mutual exclusion or coordinate the order in which processes run.

A fault where the result depends on the unpredictable timing of concurrent processes accessing shared data. It is prevented by locking, semaphores, or careful synchronisation.

A device that measures a physical quantity such as temperature or light and converts it into a signal. In control systems it provides the feedback compared with the desired value.

A device that converts an electrical control signal into physical action, such as a motor or valve. The control system drives it to reduce the difference between measured and target values.

A system that continuously measures its output, compares it with a target, and adjusts its action accordingly. Feedback lets it correct disturbances that open-loop systems cannot detect.

A document listing the tests a solution must pass, with input data, expected results, and test type. It gives evidence that the product meets its success criteria.

Values chosen to exercise a solution: normal, boundary, and erroneous data. Each type checks a different aspect of validation and robustness.

Measurable statements describing what a finished computational solution must achieve. They are agreed with the client and later used to evaluate the product objectively.