Community resourceWorksheet

OCR H446 1.1.2 CISC and RISC differences and uses

Part 1 of 5 · H446 1.1.2 · Types of processor

OCR H446 1.1.2: CISC and RISC differences and uses. Students learn to compare the same CISC and RISC features, state when general tendencies apply and use software and workload constraints.

Students will:

  • compare matching CISC and RISC features
  • qualify general tendencies rather than treating them as universal rules
  • apply software and workload constraints to processor choices

Inside: 6 explanation cells, 1 multiple-choice question, 2 fill-in-the-blanks cells and 4 written answers. 35 marks, about 55 to 70 minutes.

Series: H446 1.1.2 · Types of processor, part 1 of 5.

Shared by Coding PathwayVerified teacher

  • 13 cells
  • About 60 minutes
  • CC BY-SA 4.0
  • Shared 31 Aug 2026
  • Updated 3 Sept 2026

Preview

The whole resource, exactly as a class sees it. Answers and marking are held back.

CISC and RISC differences and uses

OCR questions compare typical CISC and RISC characteristics. Modern processors may combine features, so words such as typically and tends to are important: these are useful comparison points, not rules that every processor must follow.

One required result, different instruction-set emphasis

Illustrative CISC and RISC instruction decomposition High-level task: combine A and BStore one result using two contrasting instruction-set models CISC-style modelCOMBINE A, B, OUTone illustrative complex instructionfewer program instructionsmore work represented in hardwarean instruction may take several cycles RISC-style modelLOAD ALOAD BOPERATESTORE OUTmore simple instructionsregular form is easier to pipeline Comparison model used in OCR questionsUse “typically” or “tends to”: implementation and workload still matter.

CISC emphasises a larger set containing more complex instructions, often with variable formats and more work implemented in hardware. RISC emphasises a smaller set of simpler, more regular instructions, so one high-level operation may require a longer sequence. The diagram is illustrative; its instruction names are not a real ISA to memorise.

Compare the same feature on both sides

Feature used in the comparisonCISC tendencyRISC tendency
instruction set/formlarger, more complex, often variable lengthsmaller, simpler, more regular/fixed length
cycles per instructioncomplex instructions may need several cyclessimple instructions are modelled as one cycle
hardware/compiler emphasismore complex hardware; compiler may emit fewer instructionssimpler hardware; compiler may emit longer sequences
code/RAMfewer instructions can mean smaller code/lower RAM usemore instructions can mean larger code/more RAM use
energy/coolingtends toward higher demandtends toward lower demand
addressing/pipelinemore modes; variable work can be harder to pipelinefewer modes; regular instructions are easier to pipeline

These are relative comparison points, not guarantees of total performance.

Worked recommendation: offline inspection tablet

An inspection company needs a light, battery-powered tablet. Its existing desktop-only application cannot run on the proposed RISC platform without replacement.

  • RISC tendencies support lower energy use, less cooling and a lighter battery, which fit mobile work.
  • CISC compatibility could avoid replacing the existing software and reduce migration risk.
  • The decision depends on whether battery/weight or software continuity is the stronger constraint. A justified answer may choose either after weighing both.

This is stronger than “RISC is for mobiles” because it explains an architecture effect, a software effect and which requirement matters most.

Multiple choice1 mark

Which response is a full matched comparison?

  • ACISC typically has a larger, more complex instruction set, whereas RISC typically has a smaller, simpler set
  • BCISC has more instructions and RISC uses little energy
  • CRISC is faster because it is reduced
  • DCISC is used in desktops
Fill in the blanks4 marks
In OCR's model, CISC tends to use a gap 1 and more complex instruction set, whereas RISC tends to use a gap 2 and simpler set. CISC hardware is relatively more gap 3; RISC's regular instructions are generally easier to gap 4.
  • larger
  • smaller
  • complex
  • pipeline
  • encrypt
Written answer4 marks

Compare two differences between CISC and RISC. For each difference, discuss the same feature for both processor types. State when any cycle, pipeline or performance claim may not apply.

Choose two from instruction set/form, cycles, hardware/compiler, code/RAM, energy, addressing modes or pipeline suitability.

Students type their answer here.

Written answer8 marks

A company is choosing processors for two systems.

  1. Recommend a processor approach for a battery-powered warehouse scanner. Compare CISC and RISC using at least two relevant constraints.
  2. Recommend a processor approach for an office computer that must run an established x86-only application. Compare CISC and RISC using at least two relevant constraints.

Do not choose from the device label alone. For each system, consider software compatibility as well as hardware, energy, code or cost effects.

Students type their answer here.

Apply the comparison more widely

Use the instruction and matched-comparison models to examine software compatibility, compiler consequences and claims that sound too absolute.

Written answer8 marks

Rewrite each statement so that it is accurate.

  1. ‘Every RISC instruction always takes one cycle.’
  2. ‘CISC cannot use pipelining.’
  3. ‘RISC is always faster.’
  4. ‘CISC is only for desktops.’

For each statement, give the useful general comparison and then state the implementation or workload condition that prevents it from being a universal rule.

Students type their answer here.

Written answer6 marks

Explain how the same high-level operation can lead to different program/code and compiler consequences in the CISC and RISC models. Connect instruction count to code size/RAM and compatibility without claiming that programmers must write all applications in assembly.

Track the high-level operation through compiler translation, generated instruction sequence, code storage and software compatibility.

Students type their answer here.

Fill in the blanks4 marks
A complete CISC/RISC comparison discusses the same checkpoint gap 1 for both processor types. CISC tends to represent more work in each checkpoint gap 2, while RISC tends to use a checkpoint gap 3 sequence of simpler instructions. The better choice depends on the workload and the processor checkpoint gap 4.

Consolidate your understanding

Check that every comparison discusses the same feature for both processor types and explains why the difference matters in the stated situation. State when a general claim may be limited.