Tasks that request data at constant intervals—or periods—are known as
periodic processes. For example, an MPEG-1 video might require a rate of 30
frames per second during playback. Maintaining this rate requires that a frame
be delivered approximately every 1/30"' or 3.34 hundredths of a second. To put
this in the context of deadlines, let's assume that frame Fj succeeds frame F; in
the video playback and that frame F, was displayed at time To. The deadline
for displaying frame Fj is 3.34 hundredths of a second after time To. If the
operating system is unable to display the frame by this deadline, the frame
will be omitted from the stream.