Response time (technology)

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In technology, response time is the time a system or functional unit takes to react to a given input.

Data processing

In data processing, the response time perceived by the end user is the interval between

(a) the instant at which an operator at a terminal enters a request for a response from a computer and
(b) the instant at which the first character of the response is received at a terminal.

In a data system, the system response time is the interval between the receipt of the end of transmission of an inquiry message and the beginning of the transmission of a response message to the station originating the inquiry.[1]

Real-time Systems

In real-time systems the response time of a task or thread is defined as the time elapsed between the dispatch (time when task is ready to execute) to the time when it finishes its job (one dispatch). Response time is different from WCET which is the maximum time the task would take if it were to execute without interference. It is also different from deadline which is the length of time during which the task's output would be valid in the context of the specific system.

Display technologies

Response time is the amount of time a pixel in an LCD monitor takes to go from one value to another and back again. It is measured in milliseconds (ms). Lower numbers mean faster transitions and therefore fewer visible image artifacts.

Older monitors with long response times would create a smear or blur pattern around moving objects, making them unacceptable for moving video. Long response times can be annoying to a viewer depending on the type of data being displayed and how rapidly the image is changing or moving. Many current LCD monitor models have improved to the point that this is only seen with extreme contrasts.

For an LCD display, typical response times are 8 to 16 ms for black-white-black, or 2 to 6ms for grey-to-grey. The response time was traditionally recorded at the full black > white transition, which became the ISO standard for this specification on LCDs. Grey transitions are far more common in practice but in terms of pixel latency, they remained significantly behind the ISO transition. In recent years there have been a wide range of Response Time Compensation (RTC) / overdrive technologies[2] introduced which have allowed panel manufacturers to significantly reduce grey transitions. Response times are now commonly quoted in "GTG" (alternately but less commonly "G2G," both meaning "grey-to-grey"[3]) or "GLRT" (meaning "Gray Level Response Time"[4]). There are various names used for RTC technologies, and these vary from one manufacturer to another. Terms such as ClearMotiv (Viewsonic), AMA (BenQ), MagicSpeed (Samsung) and ODC (LG/Philips) are widely used to identify RTC enabled displays.

With a CRT the response times are much faster, and CRTs do not have the same problems with smearing or ghosting. The same is true for plasma displays. However, older CRTs and plasma displays can have problems with flicker at any refresh rate, and even newer ones can at refresh rates less than about 80Hz.

LCD screens with a slow response time are often unsuitable to play fast paced computer games. A worst-case response time of <16ms is sufficient for video gaming, and the difference between response times once below 10ms begin to become hard to perceive due to limitations of the human eye. [5] [6]

The pixel response time is often confused with the LCD input lag which adds another form of latency to pictures displayed by LCD screens. An LCD screen with high response time and significant input lag will not give satisfactory results when playing fast paced computer games or performing fast high accuracy operations on the screen (e.g. CAD). Manufacturers only state the response time of their displays and do not inform customers of the input lag value.

To address input lag, some modern televisions will offer some sort of "gaming mode" where the TV passes the signal through with minimal processing to minimize any potential image lag.

See also


  1. ^  This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).
  2. ^ "Detailed animation of overdrive technology".
  3. ^ TN Film, MVA, PVA and IPS – Which one's for you?
  4. ^ "Illustrations of GLRT and MPRT".
  5. ^ Contemporary LCD Monitor Parameters: Objective and Subjective Analysis
  6. ^ Temporal Resolution