---
title: "CPU speed atom ('rmcs')"
framework: quicktime-file-format
role: symbol
role_heading: Atom
path: quicktime-file-format/cpu_speed_atom
---

# CPU speed atom ('rmcs')

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

## Overview

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](quicktime-file-format/cpu_speed_atom/size.md)
- [Type](quicktime-file-format/cpu_speed_atom/type.md)
- [Flags](quicktime-file-format/cpu_speed_atom/flags.md)
- [CPU speed](quicktime-file-format/cpu_speed_atom/cpu_speed.md)

## See Also

### Describing reference movies

- [Reference movie atom ('rmra')](quicktime-file-format/reference_movie_atom.md)
- [Reference movie descriptor atom ('rmda')](quicktime-file-format/reference_movie_descriptor_atom.md)
- [Data reference atom](quicktime-file-format/reference_movie_data_reference_atom.md)
- [Data rate atom ('rmdr')](quicktime-file-format/data_rate_atom.md)
- [Version check atom ('rmvc')](quicktime-file-format/version_check_atom.md)
- [Component detect atom ('rmcd')](quicktime-file-format/component_detect_atom.md)
- [Movie importer component flags](quicktime-file-format/movie_importer_component_flags.md)
- [Quality atom ('rmqu')](quicktime-file-format/quality_atom.md)