SAM HARRIS TECH REVISION

OCR GCSE Computer Science - Systems Architecture Subtopics

1.1 Systems Architecture (OCR J277)

Purpose of the CPU: To process data and instructions by following the Fetch-Decode-Execute cycle.
Control Unit (CU): Coordinates CPU activities and manages the flow of data.
Arithmetic Logic Unit (ALU): Carries out mathematical calculations and logical comparisons (AND, OR, NOT).
Cache: Extremely fast memory within the CPU that stores frequently used instructions to reduce data fetch time.
Registers: Small, temporary storage locations used for specific tasks during the FDE cycle.

Concept: A design where program instructions and data are stored together in the same main memory (RAM).
Program Counter (PC): Tracks the memory address of the next instruction to be processed.
Memory Address Register (MAR): Holds the address of the location in memory where data is to be fetched or stored.
Memory Data Register (MDR): Holds the actual data or instruction that has just been fetched from or is about to be written to memory.
Accumulator (ACC): Stores the immediate results of any calculations performed by the ALU.

Clock Speed: Measured in Gigahertz (GHz); the number of Fetch-Decode-Execute cycles performed per second.
Cache Size: A larger cache provides the CPU with faster access to more data, reducing reliance on slower RAM.
Number of Cores: More cores allow a CPU to process multiple instructions simultaneously (parallel processing).

Definition: A small computer system built into a larger mechanical or electrical device to perform a specific, dedicated task.
Characteristics: Limited functions, low power consumption, and often more reliable than general-purpose computers.
Examples: Microwaves, washing machines, engine management systems, and factory controllers.