During the past decade, information technology has evolved to store and retrieve multimedia data (e.g., audio, video). Multimedia information systems utilize a variety of human senses to provide an effective means of conveying information. Already, these systems play a major role in educational applications, entertainment technology, and library information systems. A challenging task when implementing these systems is to support a continuous retrieval of an object at the bandwidth required by its media type. This is challenging because certain media types, in particular video, require very high bandwidths. For example, the bandwidth required by NTSC (the US standard established by the National Television System Committee) for network-quality video is about 45 megabits per second (mbps). Recommendation 601 of the International Radio Consultative Committee (CCIR) calls for a 216 mbps bandwidth for video objects. A video object based on the HDTV (High Definition Television) quality images requires approximately a 700 mbps bandwidth. Compare these bandwidth requirements with the typical 10 mbps bandwidth of a magnetic disk drive, which is not expected to increase significantly in the near future. Currently, there are several ways to support continuous display of these objects: 1) sacrifice the quality of the data by using either a lossy compression technique or a low resolution device, 2) employ the aggregate bandwidth of several disk drives by declustering an object across multiple disks [2], and 3) use a combination of these two techniques. Lossy compression techniques encode data into a form that consumes a relatively small amount of space, however, when the data is decoded, it yields a representation similar to the original (some loss of data). While it is effective, there are applications that cannot tolerate loss of data. As an example consider the video signals collected from space. This data may not be compressed using a lossy compression technique. Otherwise, the scientists who later uncompress and analyze the data run the risk of either observing phenomena that may not exist due to a slight change in data or miss important observations due to some loss of data.

Most implementations of workstation-based multimedia information systems cannot support a continuous display of high resolution audio and video data and suffer from frequent disruptions and delays termed hiccups. This is due to the low I/O bandwidth of the current disk technology, the high bandwidth requirement of multimedia objects, and the large size of these objects, which requires them to be almost always disk resident. A parallel multimedia information system and the key technical ideas that enable it to support a real-time display of multimedia objects are described. In this system, a multimedia object across several disk drives is declustered, enabling the system to utilize the aggregate bandwidth of multiple disks to retrieve an object in real-time. Then, the workload of an application is distributed evenly across the disk drives to maximize the processing capability of the system. To support simultaneous display of several multimedia objects for different users, two alternative approaches are described. The first approach multitasks a disk drive among several requests while the second replicates the data and dedicates resources to each individual request. The trade-offs associated with each approach are investigated using a simulation model.>