OCR Computer Science A
Level Paper 1 2026 | Study
Guide, Practice Questions,
Answers, Rationales &
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Ethics Study Guide
Updated 2026 Questions and Answers
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Included
, PC Program counter, contains the address of the next instruction
CIR Current Instruction Register: stores the address of the next instruction currently
being executed and decoded
MAR Memory Address Register, holds relevant memory address (to read from or write to)
MDR Memory Data Register, stores data being transferred to and from memory, acts as a
buffer
ALU Arithmetic and Logic Unit, does all mathematical calculations and makes all logical
decisions
Accumulator A storage register in the ALU that holds data temporarily while the data is processed
and before it is transferred to memory.
RISC Reduced Instruction Set Computer: Only simple instructions taking one clock cycle
are executed - currently more widely used than CISC
Advantages: allows for pipelining, execution will be quicker or as fast as CISC
Disadvantages: Compiler has to do more work, more RAM required
CISC Complex Instruction Set Computer: Large instruction set is used to minimise lines of
code required - mainly used for microcontrollers and embedded systems
Advantages: compiler has very little work to do, not much RAM required
Disadvantages: Building in specialised instructions can be inefficient when only
~20% get used per program
GPU Graphics Processing Unit - dedicated graphics processor on a graphics card, used
to render images stored in the RAM of the graphics card.
Multi-core CPU A CPU with more than one core on the same chip - makes use of parallel
processing for optimum efficiency
What affects processor performance? - The number of processor cores: more cores -> better performance
- The processor's clock speed: faster clock speed -> better performance
- Amount/type of cache memory: more/better cache memory -> better performance
RAM Random Access Memory - stores programs and data currently in use. Volatile
Level Paper 1 2026 | Study
Guide, Practice Questions,
Answers, Rationales &
Exam Review | Complete
Ethics Study Guide
Updated 2026 Questions and Answers
100% Verified Exam Prep and Comprehensive
Rationales
Included
, PC Program counter, contains the address of the next instruction
CIR Current Instruction Register: stores the address of the next instruction currently
being executed and decoded
MAR Memory Address Register, holds relevant memory address (to read from or write to)
MDR Memory Data Register, stores data being transferred to and from memory, acts as a
buffer
ALU Arithmetic and Logic Unit, does all mathematical calculations and makes all logical
decisions
Accumulator A storage register in the ALU that holds data temporarily while the data is processed
and before it is transferred to memory.
RISC Reduced Instruction Set Computer: Only simple instructions taking one clock cycle
are executed - currently more widely used than CISC
Advantages: allows for pipelining, execution will be quicker or as fast as CISC
Disadvantages: Compiler has to do more work, more RAM required
CISC Complex Instruction Set Computer: Large instruction set is used to minimise lines of
code required - mainly used for microcontrollers and embedded systems
Advantages: compiler has very little work to do, not much RAM required
Disadvantages: Building in specialised instructions can be inefficient when only
~20% get used per program
GPU Graphics Processing Unit - dedicated graphics processor on a graphics card, used
to render images stored in the RAM of the graphics card.
Multi-core CPU A CPU with more than one core on the same chip - makes use of parallel
processing for optimum efficiency
What affects processor performance? - The number of processor cores: more cores -> better performance
- The processor's clock speed: faster clock speed -> better performance
- Amount/type of cache memory: more/better cache memory -> better performance
RAM Random Access Memory - stores programs and data currently in use. Volatile
