On the fly

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On the fly is a phrase used to describe something that is being changed while the process that the change affects is ongoing. It is used in the automotive, computer, and culinary industries. In cars, on the fly can be used to describe the changing of the cars configuration while it is still driving. Processes that can occur while the car is still driving include switching between two wheel drive and four wheel drive on some cars and opening and closing the roof on some convertible cars. In computing, on the fly CD writers can read from one CD and write the data to another without saving it on a computer's memory. Switching computer parts on the fly means computer parts are replaced while the computer is still running. It can also be used in programming to describe changing a program while it is still running. In restaurants and other places involved in the preparation of food, the term is used to indicate that an order needs to be made right away.

Colloquial usage[edit]

In colloquial use, "on the fly" means something created when needed. The phrase is used to mean:

  1. something that was not planned ahead
  2. changes that are made during the execution of same activity: ex tempore, impromptu.

Automotive usage[edit]

In the automotive industry, the term refers to the circumstance of performing certain operations while a vehicle is driven by the engine and moving. In reference to four-wheel drive vehicles, this term describes the ability to change from two to four-wheel drive while the car is in gear and moving.[1] In some convertible models, the roof can be folded electrically on the fly, whereas in other cases the car must be stopped. In harvesting machines, newer monitoring systems let the driver track the quality of the grain, while enabling them to adjust the rotor speed on the fly as harvesting progresses.

Computer usage[edit]

A computer can compute results on the fly, or retrieve a previously stored result.

It can mean to make a copy of a removable media (CD-ROM, DVD, etc.) directly, without first saving the source on an intermediate medium (a harddisk); for example, copying a CD-ROM from a CD-ROM drive to a CD-Writer drive. The copy process requires each block of data to be retrieved and immediately written to the destination, so that there is room in the working memory to retrieve the next block of data.[2]

When used for encrypted data storage, on the fly the data stream is automatically encrypted as it is written and decrypted when read back again, transparently to software. The acronym OTFE is typically used.

On-the-fly programming is the technique of modifying a program without stopping it.[3]

A similar concept, hot swapping, refers to on-the-fly replacement of computer hardware.

Restaurant usage[edit]

In restaurants, cafes, banquet halls, and other places involved in the preparation of food, the term is used to indicate that an order needs to be made right away.[4][5][6] This is often because a previously-served dish is inedible, because a waiter has made a mistake or delayed, or because a guest has to leave promptly.[7]


  1. ^ Walczak, Jim, 4WD vs 2WD: The Differences Between 4x4 And 4x2, About.com, retrieved 2009-05-04 
  2. ^ http://www.freeotfe.org/, retrieved 2009-05-04  Missing or empty |title= (help)
  3. ^ Wang, G. E.; Cook, Perry (2002-present), On-the-fly Programming, Princeton University, retrieved 2009-05-04  Check date values in: |date= (help)
  4. ^ "The Hidden Language of Restaurant Kitchens". VICE. Retrieved 2017-02-02. 
  5. ^ "The Everything Guide to Starting and Running a Restaurant: The ultimate ... - Ronald Lee - Google Books". Books.google.com. Retrieved 2017-02-02. 
  6. ^ "Indianapolis Monthly - Google Books". Books.google.com. Retrieved 2017-02-02. 
  7. ^ "Restaurant Startup: A Practical Guide (3rd Edition) - Ravi Wazir - Google Books". Books.google.com. Retrieved 2017-02-02.