Thesis (Ph.D)--Stanford University, 1999. / Title from PDF t.p. (viewed May 9, 2002). "August 1999." "Adminitrivia V1/Prg/19990826"--Metadata.

This thesis is predicated upon a vision of the future of computing with a separation of functionality between core and edges, very similar to that governing the Internet itself. In this vision, the core of our computing infrastructure is made up of vast server farms with an abundance of storage and processing cycles. Centralization of computation in these farms, coupled with high-speed wired or wireless connectivity, allows for pervasive access to a highly-available and well-maintained repository for data, configurations, and applications. Computation in the edges is concerned with provisioning application state and user data to rich clients, notably mobile devices equipped with powerful displays and graphics processors. We define flexible computing as systems support for applications that dynamically leverage the resources available in the core infrastructure, or cloud. The work in this thesis focuses on two instances of flexible computing that are crucial to the realization of the aforementioned vision. Location flexibility aims to, transparently and seamlessly, migrate applications between the edges and the core based on user demand. This enables performing the interactive tasks on rich edge clients and the computational tasks on powerful core servers. Scale flexibility is the ability of applications executing in cloud environments, such as parallel jobs or clustered servers, to swiftly grow and shrink their footprint according to execution demands. This thesis shows how we can use system virtualization to implement systems that provide scale and location flexibility. To that effect we build and evaluate two system prototypes: Snowbird and SnowFlock. We present techniques for manipulating virtual machine state that turn running software into a malleable entity which is easily manageable, is decoupled from the underlying hardware, and is capable of dynamic relocation and scaling. This thesis demonstrates that virtualization technology is a powerful and suitable tool to enable solutions for location and scale flexibility.

An active object system is a transition-based object-oriented system suitable for the design of various concurrent systems. An AOS consists of a collection of interacting objects, where the behavior of each object is determined by the transition statements provided in the class of that object. A transition statement is a condition-action pair, an equational assignment statement, or an event routine. The transition statements provided for each object can access, besides the state of that object, the states of the other objects known to it through its interface variables. Interface variables are bound to objects when objects are instantiated so that desired connections among objects are established. The major benefit of the AOS approach is that an active system can be hierarchically composed from its active software components as if it were a hardware system. An AOS provides better encapsulation and more flexible communication protocols than ordinary object oriented systems, since control within an AOS is localized. / Graduation date: 1992

Kernel patches are frequently released to fix security vulnerabilities and bugs. However, users and system administrators often delay installing these updates because they require a system reboot, which results in disruption of service and the loss of application state. Unfortunately, the longer an out-of-date system remains operational, the higher is the likelihood of a system being exploited. Approaches, such as dynamic patching and hot swapping, have been proposed for updating the kernel. All of them either limit the types of updates that are supported, or require significant programming effort to manage. We have designed a system that checkpoints application-visible state, updates the kernel, and restores the application state. By checkpointing high-level state, our system no longer depends on the precise implementation of a patch and can apply all backward compatible patches. The results show that updates to major kernel releases can be applied with minimal changes.

This thesis is predicated upon a vision of the future of computing with a separation of functionality between core and edges, very similar to that governing the Internet itself. In this vision, the core of our computing infrastructure is made up of vast server farms with an abundance of storage and processing cycles. Centralization of computation in these farms, coupled with high-speed wired or wireless connectivity, allows for pervasive access to a highly-available and well-maintained repository for data, configurations, and applications. Computation in the edges is concerned with provisioning application state and user data to rich clients, notably mobile devices equipped with powerful displays and graphics processors. We define flexible computing as systems support for applications that dynamically leverage the resources available in the core infrastructure, or cloud. The work in this thesis focuses on two instances of flexible computing that are crucial to the realization of the aforementioned vision. Location flexibility aims to, transparently and seamlessly, migrate applications between the edges and the core based on user demand. This enables performing the interactive tasks on rich edge clients and the computational tasks on powerful core servers. Scale flexibility is the ability of applications executing in cloud environments, such as parallel jobs or clustered servers, to swiftly grow and shrink their footprint according to execution demands. This thesis shows how we can use system virtualization to implement systems that provide scale and location flexibility. To that effect we build and evaluate two system prototypes: Snowbird and SnowFlock. We present techniques for manipulating virtual machine state that turn running software into a malleable entity which is easily manageable, is decoupled from the underlying hardware, and is capable of dynamic relocation and scaling. This thesis demonstrates that virtualization technology is a powerful and suitable tool to enable solutions for location and scale flexibility.

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Thesis (MTech. degree in Information Networks)--Tshwane University of Technology, 2009. / With this research, we focus on utilizing a distributed file system to combat congestion problems in wireless networks. The Coda file system is our choice of a distributed file system, as it offers several services, such as data pre-fetching, hoarding of files, disconnected operation and data consistency.

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