--- title: "Design metrics of embedded system" subject: "Embedded System" chapter: 1 key: "semester_6/embedded_system:design-metrics-embedded" source: https://www.bctengineer.com/q/semester_6/embedded_system/design-metrics-embedded site: BCT Engineering --- # Design metrics of embedded system Embedded System · Chapter 1: Introduction to Embedded System - Asked in: 2076 Baisakh, 4 marks; 2078 Chaitra; 2075 Baisakh, 4 marks (asked 3 times) - Video: [Design metrics of embedded system | Introduction to Embedded System | Embedded System & RTOS](https://www.youtube.com/watch?v=xfXe7xQhKFU) — Ekeeda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/embedded_system/design-metrics-embedded - Whole chapter: https://www.bctengineer.com/md/semester_6/embedded_system/chapter-1 ## Question Define design metric and explain the various (important) design metrics of an embedded system. ## Short answer A design metric is a measurable feature of a system implementation that designers optimize, with trade-offs between competing metrics. Key metrics include NRE cost, unit cost, size, performance (latency/throughput), power, flexibility, time-to-market, and reliability. ## Answer A **design metric** is a measurable feature of a system's implementation. Designers must optimise several metrics at once, and these metrics usually compete with each other (improving one worsens another). This is the *design-metric (optimisation) challenge*. #### Important design metrics - **NRE cost (non-recurring engineering):** the one-time cost of designing the system. It is paid once, however many units are made. - **Unit cost:** the cost of manufacturing each copy (excluding NRE). Total cost = NRE + unit cost × number of units. - **Size:** physical space or memory, measured in bytes (software), gates (hardware) or cm³. - **Performance:** execution time. It includes *latency* (time for one task) and *throughput* (tasks per second). - **Power:** the power consumed; it decides battery life, heat and cooling. - **Flexibility:** the ability to change functionality without large extra NRE. - **Time-to-prototype:** the time needed to build a working version. - **Time-to-market:** the time until the product can be sold. Late entry loses revenue. - **Maintainability:** how easily the system can be modified after release. - **Correctness:** confidence that the system implements its functionality correctly. - **Safety:** the probability that the system will not cause harm. - **Reliability** is also commonly listed with these. #### Competing example Using a faster processor improves performance but raises unit cost and power. A custom single-purpose chip gives high performance and low power but has high NRE and low flexibility. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is optimising design metrics called a challenge? A. Metrics are unmeasurable B. Metrics usually compete, so improving one worsens another C. Only one metric matters D. Metrics only apply to software Answer: B. Designers must optimise several metrics at once, and they compete, e.g. higher performance costs more power and money. (Key point: Design metric and challenge) 2. What is NRE cost? A. The cost of manufacturing each unit B. The cost of repairing units C. The one-time cost of designing the system, paid once however many units are made D. The cost of packaging Answer: C. NRE is the one-time design cost; unit cost is per copy. Total cost = NRE + unit cost x number of units. (Key point: NRE vs unit cost) 3. Which pair correctly describes the two measures of performance? A. Latency is tasks per second; throughput is time for one task B. Both mean memory size C. Both mean power consumption D. Latency is time for one task; throughput is tasks per second Answer: D. Latency is the time for one task, throughput is the number of tasks per second. (Key point: Performance) 4. A custom single-purpose chip typically gives which trade-off? A. High performance and low power but high NRE and low flexibility B. Low NRE and high flexibility C. High power and low performance D. Low NRE and short time-to-market Answer: A. A custom chip is fast and low power but needs high NRE and cannot be changed easily. (Key point: Competing metrics example) ## Related in Embedded System - [Metrics for control objectives](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Acontrol-metrics-objectives) — Embedded System, chapter 7 - [Define embedded system and its applications](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Adefine-embedded-system-applications) — Embedded System, chapter 1, asked 4× - [Define embedded system and its characteristics](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Adefine-embedded-system-characteristics) — Embedded System, chapter 1, asked 2× - [Digital camera as embedded system](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Adigital-camera-embedded-example) — Embedded System, chapter 1, asked 2× - [Embedded system types and definition difficulty](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aembedded-types-hard-to-define) — Embedded System, chapter 1 - [Processor is heart of embedded system](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aprocessor-heart-structural-units) — Embedded System, chapter 2 ## Related in other subjects - [Design goals and performance metrics](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Adesign-goals-metrics) — Computer Organization and Architecture, chapter 1 - [Design steps and criteria of distribution system](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Adistribution-design-steps) — Water Supply Engineering, chapter 7, asked 3× - [KUKL customer system design and code](https://www.bctengineer.com/question.md?key=semester_6%2Fobject_oriented_analysis_and_design%3Akukl-use-case-class-diagram-code) — Object Oriented Analysis and Design, chapter 4 - [Recommender system design and types](https://www.bctengineer.com/question.md?key=semester_8%2Finformation_system%3Arecommender-design-types) — Information System, chapter 7