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In general, turnaround time (TAT) means the amount of time taken to fulfill a request. The concept thus overlaps with lead time and can be contrasted with cycle time.
In computing, turnaround time is the total time taken between the submission of a program/process/thread/task (Linux) for execution and the return of the complete output to the customer/user. It may vary for various programming languages depending on the developer of the software or the program. Turnaround time may simply deal with the total time it takes for a program to provide the required output to the user after the program is started.
In case of batch systems, turnaround time will include time taken in forming batches, batch execution and printing results.
With increasing computerization of analytical instruments the distinction between a computing context and a "non-computing" context is becoming semantic. An example of a "non-computing" context of turnaround time is the time a particular analysis in a laboratory, such as a medical laboratory, other commercial laboratories or a public health laboratory takes to result. Laboratories may publish an average turnaround time to inform their clients, e.g. a health care worker ordering the test, after what time a result can be expected. A prolonged turnaround time may give the requester a clue that a specimen was not received, that an analysis met with problems within the lab including that the result was unusual and the test was repeated for quality control.