Response time
In technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...

, response time is the time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

 a system
System is a set of interacting or interdependent components forming an integrated whole....

 or functional unit takes to react to a given input.

Data processing

In data processing
Data processing
Computer data processing is any process that a computer program does to enter data and summarise, analyse or otherwise convert data into usable information. The process may be automated and run on a computer. It involves recording, analysing, sorting, summarising, calculating, disseminating and...

, the response time perceived by the end user is the interval between the instant at which an operator at a terminal
Terminal (telecommunication)
In the context of telecommunications, a terminal is a device which is capable of communicating over a line. Examples of terminals are telephones, fax machines, and network devices - printers and workstations....

 enters a request for a response from a computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 and the instant at which the first character
Character (computing)
In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language....

 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
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...

 of an inquiry message
A message in its most general meaning is an object of communication. It is a vessel which provides information. Yet, it can also be this information. Therefore, its meaning is dependent upon the context in which it is used; the term may apply to both the information and its form...

 and the beginning of the transmission of a response message to the station originating the inquiry.

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
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....

 monitor takes to go from one value to another and back again. It is measured in millisecond
A millisecond is a thousandth of a second.10 milliseconds are called a centisecond....

s (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(which?) 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 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") or "GLRT" (meaning "Gray Level Response Time"). 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
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

 the response times are much faster, and CRTs do not have the same problems with smearing or ghosting. The same is true for plasma display
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...

s. However, older CRTs and plasma displays can have problems with flicker
Flicker fusion threshold
The flicker fusion threshold is a concept in the psychophysics of vision. It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the observer...

 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.

The pixel response time is often confused with the LCD input lag
Input lag
Display lag is a phenomenon associated with some types of LCD displays, and nearly all types of HDTVs, that refers to latency, or lag measured by the difference between the time a signal is input into a display and the time it is shown by the display. This lag time has been measured as high as...

 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
Computer-aided design
Computer-aided design , also known as computer-aided design and drafting , is the use of computer technology for the process of design and design-documentation. Computer Aided Drafting describes the process of drafting with a computer...

). Manufacturers only state the response time of their displays and do not inform customers of the input lag
Input lag
Display lag is a phenomenon associated with some types of LCD displays, and nearly all types of HDTVs, that refers to latency, or lag measured by the difference between the time a signal is input into a display and the time it is shown by the display. This lag time has been measured as high as...


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

  • Latency (engineering)
    Latency (engineering)
    Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...

  • Interrupt latency
    Interrupt latency
    In real-time operating systems, interrupt latency is the time between the generation of an interrupt by a device and the servicing of the device which generated the interrupt. For many operating systems, devices are serviced as soon as the device's interrupt handler is executed...

  • Application Response Measurement
    Application Response Measurement
    Application Response Measurement is an open standard published by the Open Group for monitoring and diagnosing performance bottlenecks within complex enterprise applications that use loosely-coupled designs or service-oriented architectures....

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.