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# CPU speed atom ('rmcs')

A CPU speed atom specifies the minimum computing power needed to display a movie.

## Overview

A CPU speed atom specifies the minimum computing power needed to display a movie. QuickTime performs an internal test to determine the speed of the user’s computer.

This is not a simple measurement of clock speed — it is a measurement of performance for QuickTime-related operations. Speed is expressed as a relative value between `100` and `2^31`, in multiples of `100`.

Applications play the movie with the highest specified CPU speed that is less than or equal to the user’s speed. If the user’s speed is lower than any movie’s CPU speed, applications play the movie with the lowest CPU speed requirement. The movie with the highest CPU speed is assumed to be the highest quality.

Only one CPU speed atom is allowed in a given reference movie descriptor atom.

## Topics

### Data fields

[`Size`](/documentation/quicktime-file-format/CPU_speed_atom/Size)

The number of bytes in this CPU speed atom.

[`Type`](/documentation/quicktime-file-format/CPU_speed_atom/Type)

The type of this atom.

[`Flags`](/documentation/quicktime-file-format/CPU_speed_atom/Flags)

A 32-bit integer that is always 0.

[`CPU speed`](/documentation/quicktime-file-format/CPU_speed_atom/CPU_speed)

A relative ranking of required computer speed, expressed as a 32-bit integer divisible by 100, with larger numbers indicating higher speed.


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