How Do RISC and CISC Architectures Affect Program Speed?

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SUMMARY

The discussion focuses on the performance comparison between RISC and CISC architectures, specifically analyzing execution times for various instructions. In the example provided, a CISC computer takes significantly longer to execute a program with 10 million additions, 30 million multiplications, 35 million memory instructions, and 15 million branches compared to a RISC computer. The speedup ratio is calculated based on the total execution times, demonstrating that RISC architectures can outperform CISC in specific scenarios. Additionally, the discussion highlights that MIPS (Million Instructions Per Second) does not account for all program execution factors, such as I/O operations, which can lead to misleading performance assessments.

PREREQUISITES
  • Understanding of RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) architectures
  • Familiarity with performance metrics such as MIPS (Million Instructions Per Second)
  • Basic knowledge of instruction execution cycles and their impact on program speed
  • Ability to perform calculations related to speedup ratios and execution times
NEXT STEPS
  • Research the differences in instruction sets between RISC and CISC architectures
  • Learn how to calculate speedup ratios in computer architecture
  • Explore the implications of MIPS as a performance metric and its limitations
  • Investigate the impact of I/O operations on overall program execution time
USEFUL FOR

This discussion is beneficial for computer architects, performance analysts, and software developers interested in optimizing program execution speed and understanding the implications of architectural design choices.

loonny01
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1st ques :
In a CISC computer, the instructions addition, multiplication, memory and branch
all take 20 cycles each while in a RISC computer, the execution time is given
below:
addition - 2 cycles
multiplication - 20 cycles
memory - 10 cycles
branch - 4 cycles
Calculate the speedup ratio for a program with 10 million additions, 30 million
multiplications, 35 million memory instructions and 15million branch
instructions. Explain!...

2nd ques:
When running a particular program, computer A achieves 100 MIPS(million
instructions per second) and computer B achives 75 MIPS. However, computer A
takes 60 seconds to execute a program while computer B takes only 45s. How is
this possible?

Really thanz to any1 who willing 2ans this ques!
 
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Hint(s) for #1:
How long would the program take to run on the CISC computer?
How long would the program take to run on the RISC computer?
Which one is faster? Why? By how much? What is the definition of speedup you are using... a formula, perhaps?

Hint(s) for #2:
What does MIPS measure?
Is this the only thing that a program does... or are there other things a program can do that this measure doesn't take into account (I/O, for instance?)
Could things like this make MIPS more or less irrelevant?
 

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