![]() However, consider package shipment and delivery alerts or ecommerce stock availability notifications. Minutes: Waiting minutes may seem like an eternity to a high-frequency trading application. Reducing the response time by one tenth of a second (100ms), which may be costly to implement, has no change in value for the application. These real-time applications drive actions and decisions that are made in human-reaction time rather than machine-time. Sub-minute processing time is often more than good enough for applications that process log files, computing analytics on event streams, as well as alerting applications. We’re still in the realm of real-time, but we are now venturing into near real-time. The decision on what optimal ad to display or whether there is enough balance to let a cellphone call proceed must be made on the order of 100 milliseconds. Real-time applications that worry about latency in milliseconds include telecom applications, digital ad networks, and self-driving cars. Network performance is often measured in milliseconds. To put this in context, the speed of a human eye blink is 100 to 400 milliseconds, or between a 10th and half of a second. Milliseconds: A millisecond (ms) is one one-thousandth of a second. A trading decision has to be made in as few microseconds as possible in order to execute ahead of competition and thus maximize profit. Financial trading firms spend large sums of money investing in the latest networking and computer hardware to eliminate microseconds of latency within their trading platforms. Real-time applications that worry about microsecond latency are high-frequency trading (HFT) applications. Microseconds: A microsecond (µs) is one millionth of a second. ![]() Worrying about nanosecond latency is at the bleeding edge of real-time computing and is primarily driven by innovation with hardware and networking technology. With this in mind, it is easy to see why nanoseconds are the unit used to measure the speed of hardware, such as the time it takes to access computer memory. This quick video of Hopper is worth watching if you haven’t yet seen it. Admiral Grace Hopper famously explained a nanosecond using an 11.8-inch wire, as that is the maximum distance electricity can travel in one nanosecond. Nanoseconds: A nanosecond (ns) is one billionth of a second. Rather than look at applications and determine if they are real-time or not, let’s examine various time units and understand the types of real-time applications that require those response rates: While this definition continues with the subjective theme, it does confirm that the correct answer to how to measure real-time is “All of the above.” The meaning of the term real-time varies based on application need-the amount of time a computer (the application) takes to respond and the acceptable latency is as fast as required by the problem domain. Real-time- “of or relating to applications in which the computer must respond as rapidly as required by the user or necessitated by the process being controlled.”
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