Editing Response time (technology) (section)

== Computing ==
In computing, the [[responsiveness]] of a service, how long a system takes to respond to a request for service, is measured through the response time. That service can be anything from a{{Citation needed|date=May 2024}} memory fetch, to a disk IO, to a complex database query, or loading a full web page. Ignoring transmission time for a moment, the response time is the sum of the service time and wait time. The service time is the time it takes to do the work you requested. For a given request the service time varies little as the workload increases – to do X amount of work it always takes X amount of time. The wait time is how long the request had to wait in a [[Queue (abstract data type)|queue]] before being serviced and it varies from zero, when no waiting is required, to a large multiple of the service time, as many requests are already in the queue and have to be serviced first.{{Original research inline|date=May 2024}}

With basic queueing theory math<ref>{{cite book  | last = Wescott | first = Bob | title = The Every Computer Performance Book, Chapter 3: Useful laws | publisher = [[CreateSpace]] | date = 2013  | isbn = 978-1482657753}}</ref> you can calculate how the average wait time increases as the device providing the service goes from 0-100% busy. As the device becomes busier, the average wait time increases in a [[Nonlinear system|non-linear]] fashion. The busier the device is, the more dramatic the response time increases will seem as you approach 100% busy; all of that increase is caused by increases in wait time, which is the result of all the requests waiting in queue that have to run first.

Transmission time gets added to response time when your request and the resulting response has to travel over a network and it can be very significant.<ref>{{cite journal | last = Leighton | first = Tom | journal = Communications of the ACM | volume = 52 | issue = 2 | pages = 44–51 | title = Improving Performance on the Internet | year = 2009 | doi = 10.1145/1461928.1461944 | s2cid = 18190700 | doi-access = free }}</ref> Transmission time can include [[Propagation delay#Networking|propagation delays]] due to distance (the speed of light is finite), delays due to [[Error detection and correction#Internet|transmission errors]], and data communication bandwidth limits (especially at the [[Last mile (telecommunications)|last mile]]) slowing the transmission speed of the request or the reply.

Developers can reduce the response time of a system (for end users or not) using [[program optimization]] techniques.