Study guide: Compare Systems under Explicit Constraints
Compare a model with 40 tasks at 8 tasks/s, latency samples[1,1,1,1,8]seconds and a 50 Wdevice used 4 hours. Report duration,mean,max and bounded energy.
Ideas to explain in your own words
- Throughput is work completed per unit time. It differs from latency for an individual request. The supplied system model completes independent tasks at a constant rate with no setup time; dividing tasks by rate estimates batch duration. Real systems may have concurrency limits and variable work.
- An average latency can hide a slow request. Looking at the ordered distribution or a maximum reveals another aspect of performance. Our small supplied list is not a validated service benchmark or a percentile guarantee; it simply demonstrates why a single average does not describe every observation.
- Energy use can be modeled as power multiplied by time. Watts times hours gives watt-hours; dividing by 1000 gives kilowatt-hours. The supplied power is constant and measured in watts. This model does not include cooling,network equipment or an entire lifecycle, so its boundary must be stated.
- A system choice depends on constraints and priorities. Lower cost,latency,energy or maintenance burden can conflict. A decision should state which criteria are required and which tradeoff is accepted. The exercise uses supplied fictional comparison notes and does not recommend a paid product.
Useful vocabulary
- throughput
- Work completed per unit time.
- latency
- Time for an individual request or task.
- system boundary
- The components included in a model.
Watch your reasoning
- A high average throughput does not guarantee every individual request has low latency.
- The maximum in five samples does not certify a production percentile.
- Do not call a device-only estimate the whole service’s lifecycle footprint.
- The smallest single number does not automatically identify the best overall system.
A worked review example
Ideal model completes 6 tasks per second. Duration for 24 tasks, excluding setup and contention? The supported answer is 4 seconds. Applying the stated rule gives 4 seconds. Divide total tasks by the stated constant throughput using matching time units. A high average throughput does not guarantee every individual request has low latency. Calculation: (24/6) = 4.0. OptionA has verified offline and keyboard support. Required: works offline and supports keyboard tasks. Choose the supplied conclusion. The supported answer is Meets both requirements. Eliminate options that fail required constraints, then explain the remaining tradeoff. The smallest single number does not automatically identify the best overall system. The supplied facts, rather than an assumed real-world detail, determine this paper case. Compare the recorded action or value with the stated rule before choosing an answer.
Make a practice plan
- Make a four-row summary, one row for each lesson, with its computing idea and one worked decision.
- Explain one tempting mistake using the actual supplied example.
- Complete the new unit review before consulting its explanations.
- Try the transfer task on paper and compare your evidence against the model response.