OCR A-Level 1.1 - Structure and Function of the Processor

Vocabulary flashcards covering CPU components, registers, buses, performance factors, and computer architectures based on the OCR A-Level specification.

Central Processing Unit (CPU)

The most important component in every computer system, responsible for processing data and instructions by constantly repeating the fetch-decode-execute cycle.

Control Unit (CU)

A component of the CPU that directs the flow of data and instructions and manages the FDE cycle, especially the decoding of instructions.

Arithmetic Logic Unit (ALU)

A component of the CPU that performs all arithmetic calculations and logical operations.

Registers

Small, ultra-fast storage locations inside the CPU that temporarily hold data, instructions, or addresses during processing.

Cache memory

Temporary storage space for frequently accessed data and instructions inside the CPU, reducing the time needed to access RAM.

Program Counter (PC)

A register that stores the memory address of the next instruction to be fetched from RAM.

Memory Address Register (MAR)

A register that stores the memory address currently being accessed, which may be an instruction or data.

Memory Data Register (MDR)

A register that stores the data that is transferred from RAM to the CPU.

Current Instruction Register (CIR)

A register that stores the instruction that has been fetched from RAM.

Accumulator (ACC)

A register that stores data currently being processed and the result of calculations or logical operations made by the ALU.

Buses

Internal connections across which data and signals are transmitted between components.

Data bus

A bidirectional bus that transmits data and instructions between the CPU, memory, and other components such as input/output devices.

Address bus

A unidirectional bus that transmits the location in memory that the CPU is accessing, traveling from the CPU to RAM.

Control bus

A bidirectional bus that transmits control signals (e.g. 'read' or 'write') from the CPU to coordinate other components.

Fetch-Decode-Execute (FDE) cycle

The cycle performed by the CPU millions of times per second where instructions are fetched from RAM, decoded (understood), and executed (processed).

Clock speed

The number of cycles a CPU performs per second; higher speeds allow more instructions to be executed per second.

Number of cores

A factor in CPU performance where more units allow a CPU to carry out multiple instructions simultaneously, improving multitasking and parallel processing.

Pipelining

The concurrent processing of multiple instructions where an instruction can be fetched while another is decoded and another is executed.

Computer architecture

The design and organisation of a system’s components and how they interact.

Von Neumann architecture

A design that uses a single main memory (RAM) to store both program instructions and data, which can cause a bottleneck as they travel along the same buses.

Harvard architecture

A design that separates the storage of program instructions and data into two different memory locations, allowing them to be fetched at the same time.

Contemporary architecture

Modern architecture including features such as onboard graphics, performance boosting mode, out-of-order execution, and virtual cores.

Apollo Guidance Computer (AGC) clock speed

The clock speed of the NASA Apollo 11 mission computer was approximately $1\,MHz$, which is slower than many modern GCSE-level calculators.