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Communications of the ACM

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Computation Takes Time, But How Much?

Computation Takes Time, illustration

Credit: Alicia Kubista / Andrij Borys Associates

A few years ago, in the pages of this magazine, Edward Lee argued that computing needs time.23 This article focuses on the natural assumption that computing also takes time. We examine the problem of determining how much time. It is the problem of verifying the real-time behavior of safety-critical embedded systems. For such systems, for example, anti-lock brakes and airbags, punctual behavior is of utmost importance: If the controlling computations take too long, quality of service degrades or the systems fail completely—your braking distance is longer or your head hits the steering wheel, respectively.

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Key Insights


The basis for verifying the timeliness of system reactions is reliable information on the execution times of all computational tasks involved. It is the job of timing analysis, also called worst-case execution-time (WCET) analysis, to determine such information.


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