Flexible disk scheduling for multimedia presentation servers

Objects composing a multimedia presentation need to be delivered based on the temporal relationships specified by the author(s). Hence, even discrete media objects (that do not normally have any real-time characteristics) have temporal constraints on their presentations. Composition of multimedia presentations can vary widely. Based on their composition, we can consider three broad categories of multimedia presentations: heavy, medium, and light. Heavy multimedia presentations comprise video and audio for the entire duration along with text and images. Medium multimedia presentations are composed of text, images, audio, and short video clips, distributed over the entire duration of the presentations. Light multimedia presentations consist of mostly text, images, and audio. There may not be any video clips (if there are, then very few) as part of the multimedia presentation. This varying nature of the composition of multimediapresentations provides some flexibility for scheduling their retrieval. Depending on the composition of multimedia presentations, disk access for retrieval may not be needed in every round. For instance, a medium multimedia presentation may need few slots once in, say, every fivelsix rounds, since the client will take time to consume (view) the presentation. Hence, a presentation can skip a certain number of disk scheduling rounds before retrieving the next required chunk of data.