This article provides a retrospective of our original paper by the same title in the Proceedings of the First ACM Conference on Multimedia, published in 1993. This article examines the problem of disk scheduling in a multimedia I/O system. In a multimedia server, the disk requests may have constant data rate requirements and need guaranteed service. We propose a new scheduling algorithm, SCAN-EDF, that combines the features of SCAN type of seek optimizing algorithm with an Earliest Deadline First (EDF) type of real-time scheduling algorithm. We compare SCAN-EDF with other scheduling strategies and show that SCAN-EDF combines the best features of both SCAN and EDF. We also investigate the impact of buffer space on the maximum number of video streams that can be supported.We show that by making the deadlines larger than the request periods, a larger number of streams can be supported.We also describe how we extended the SCAN-EDF algorithm in the PRISM multimedia architecture. PRISM is an integrated multimedia server, designed to satisfy the QOS requirements of multiple classes of requests. Our experience in implementing the extended SCAN-EDF algorithm in a generic operating system is discussed and performance metrics and results are presented to illustrate how the SCAN-EDF extensions and implementation strategies have succeeded in meeting the QOS requirements of different classes of requests.

In this paper, we look at the problem of disk scheduling in a multimedia I/O system.In a multimedia server, the disk requests may have constant data rate requirements and need guaranteed service.We propose a new scheduling algorithm, SCAN-EDF, that combines the features of SCAN type of seek optimizing algorithms with Earliest Deadline First (EDF) type of real-time scheduling algorithms.We compare SCAN-EDF with other scheduling strategies and show that SCAN-EDF combines the best features of both SCAN and EDF.We also investigate the impact of buffer space on the maximum number of video streams that can be supported.We show that by making the deadlines larger than the request periods, a larger number of streams can be supported.

This paper presents our experience with implementing atomicity in two systems: the QuickSilver distributed file system and the Starburst relational database manager. Each of these systems guarantees that certain collections of operations done on behalf of their clients execute atomically, despite process, machine, or network failures. In this paper we describe the atomic properties implemented by each system, present the algorithms and mechanisms used, examine the similarities and differences between the two systems, and give the rationale for different design decisions. We demonstrate that the support of atomicity with high performance requires a variety of techniques carefully chosen to balance the amount of data logged, the level of concurrency allowed, and the mutual consistency requirements of sets of objects, The main goal is to help others implement efficient systems that support atomicity.>

All programs in the QuickSilver distributed system behave atomically with respect to their updates to permanent data. Operating system support for transactions provides the framework required to support this, as well as a mechanism that unifies reclamation of resources af- ter failures or normal process termination. This paper evaluates the use of transactions for these purposes in a general purpose operating system and presents some of the lessons learned from our experience with a complete running system based on transactions. Examples of how transactions are used in QuickSilver and mea- surements of their use demonstrate that the transaction mechanism provides an efficient and powerful means for solving many of the problems introduced by operating system extensibility and distribution.

QuickSilver is a distributed operating system that is intended for large, geographically dispersed systems. The authors describe how clients and data servers interact in the QuickSilver system to access distributed data in the context of large, geographically dispersed systems in which there are many different kinds of data servers. An interface is defined that provides a uniform way for clients and servers to exchange information about each other and to access data objects. The interface attempts to minimize the number of messages needed for this. It supports efficient interaction with higher-level client and server semantics by appropriate use of high-level abstractions and operations, and by selectively exposing the parameters governing communication connections to higher layers of the software.>