RISC vs CISC design philosophy in ARM Architecture - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the main goal of RISC architecture.

ARM Architecture

The primary goal of RISC is to have [1] instructions that execute quickly.

Drag options to blanks, or click blank then click option'

Aslow

Bcomplex

Cvariable-length

Dsimple

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'complex' because of confusion with CISC.

RISC stands for Reduced Instruction Set Computer, focusing on simple instructions for faster execution.

2fill in blank

medium

Complete the code to describe CISC instruction length.

ARM Architecture

CISC instructions are often [1] in length to perform complex tasks.

Drag options to blanks, or click blank then click option'

Avariable

Bsimple

Cfixed

Dshort

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'fixed' because of confusion with RISC.

CISC stands for Complex Instruction Set Computer, where instructions can vary in length to handle complex operations.

3fill in blank

hard

Fix the error in the statement about RISC and CISC execution speed.

ARM Architecture

RISC processors generally execute instructions [1] than CISC processors.

Drag options to blanks, or click blank then click option'

Aslower

Bequally

Cfaster

Drandomly

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'slower' due to misunderstanding of instruction complexity.

RISC processors use simpler instructions that typically execute faster than the more complex CISC instructions.

4fill in blank

hard

Fill both blanks to complete the comparison of RISC and CISC instruction sets.

ARM Architecture

RISC uses [1] instructions, while CISC uses [2] instructions.

Drag options to blanks, or click blank then click option'

Asimple

Bfast

Ccomplex

Dslow

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up which architecture uses simple or complex instructions.

RISC uses simple instructions for speed, whereas CISC uses complex instructions to do more work per instruction.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension about instruction types.

ARM Architecture

instruction_types = [1]: '[2]' for [3] in ['RISC', 'CISC']}

Drag options to blanks, or click blank then click option'

Ainst

Bsimple

Cx

Dcomplex

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'inst' as key variable name instead of loop variable.

This dictionary comprehension creates a mapping where each instruction type is labeled as 'simple'. This is a trick question to test understanding of syntax and variable naming.

Practice

1. What is the main idea behind the RISC design philosophy?

easy

A. Use complex instructions that do more work

B. Focus on reducing power consumption only

C. Use simple and fast instructions

D. Use instructions that are all the same length

Solution

1. Step 1: Understand RISC basics

   RISC stands for Reduced Instruction Set Computer, which means it uses fewer, simpler instructions.

2. Step 2: Compare with CISC

   Unlike CISC, which uses complex instructions, RISC focuses on simple and fast instructions.

3. Final Answer:

   Use simple and fast instructions -> Option C

4. Quick Check:

   RISC = simple, fast instructions [OK]

Hint: RISC means simple instructions, CISC means complex [OK]

Common Mistakes:

• Confusing RISC with CISC
• Thinking RISC uses complex instructions
• Assuming RISC focuses only on power

2. Which of the following is a characteristic of CISC instruction sets?

easy

A. Instructions only use registers, no memory access

B. Instructions are all the same size

C. Instructions are very simple and fast

D. Instructions can perform multiple operations

Solution

1. Step 1: Recall CISC features

   CISC stands for Complex Instruction Set Computer, meaning instructions can do multiple tasks.

2. Step 2: Identify correct feature

   CISC instructions often combine several operations into one instruction.

3. Final Answer:

   Instructions can perform multiple operations -> Option D

4. Quick Check:

   CISC = complex, multi-operation instructions [OK]

Hint: CISC instructions do more work per instruction [OK]

Common Mistakes:

• Thinking CISC instructions are all the same size
• Confusing CISC with RISC simplicity
• Assuming CISC avoids memory access

3. Consider a processor that executes 4 simple instructions in 1 cycle each (RISC) versus 2 complex instructions in 2 cycles each (CISC). Which completes more instructions in 4 cycles?

medium

A. RISC completes 4 instructions

B. CISC completes 4 instructions

C. RISC completes 2 instructions

D. CISC completes 2 instructions

Solution

1. Step 1: Calculate RISC instructions done

   RISC does 1 instruction per cycle, so in 4 cycles it completes 4 instructions.

2. Step 2: Calculate CISC instructions done

   CISC does 1 instruction in 2 cycles, so in 4 cycles it completes 2 instructions.

3. Final Answer:

   RISC completes 4 instructions -> Option A

4. Quick Check:

   RISC faster with simple instructions [OK]

Hint: Count instructions per cycle to compare speed [OK]

Common Mistakes:

• Assuming complex instructions always finish faster
• Mixing cycles per instruction
• Ignoring instruction count per cycle

4. A programmer writes code assuming all instructions take the same time, but the processor uses CISC design. What problem might occur?

medium

A. Code timing is inaccurate due to variable instruction lengths

B. Code runs faster than expected

C. Code will not compile

D. Code uses less memory

Solution

1. Step 1: Understand CISC instruction timing

   CISC instructions vary in length and complexity, so execution time varies.

2. Step 2: Identify timing impact

   Assuming equal time causes inaccurate timing predictions and possible bugs.

3. Final Answer:

   Code timing is inaccurate due to variable instruction lengths -> Option A

4. Quick Check:

   CISC instructions vary in time, causing timing errors [OK]

Hint: CISC instructions vary in length and time [OK]

Common Mistakes:

• Thinking code won't compile
• Assuming code runs faster always
• Ignoring timing differences

5. A device needs to run simple tasks very fast and save power. Which design philosophy suits it best and why?

hard

A. CISC, because complex instructions reduce code size

B. RISC, because simple instructions use less power and run faster

C. CISC, because it uses fewer instructions overall

D. RISC, because it uses complex instructions to do more work

Solution

1. Step 1: Analyze device needs

   The device needs speed and low power for simple tasks.

2. Step 2: Match design philosophy

   RISC uses simple, fast instructions that consume less power, fitting the need.

3. Final Answer:

   RISC, because simple instructions use less power and run faster -> Option B

4. Quick Check:

   Simple fast tasks = RISC best fit [OK]

Hint: Simple fast tasks favor RISC for power and speed [OK]

Common Mistakes:

• Choosing CISC for simple fast tasks
• Confusing instruction complexity with speed
• Ignoring power consumption