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Numerous systems have been designed which use virtualization to subdivide the ample resources of a modern computer. Some require specialized hardware, or cannot support commodity operating systems. Some target 100% binary compatibility at the expense of performance. Others sacrifice security or functionality for speed. Few offer resource isolation or performance guarantees; most provide only best-effort provisioning, risking denial of service.This paper presents Xen, an x86 virtual machine monitor which allows multiple commodity operating systems to share conventional hardware in a safe and resource managed fashion, but without sacrificing either performance or functionality. This is achieved by providing an idealized virtual machine abstraction to which operating systems such as Linux, BSD and Windows XP, can be ported with minimal effort.Our design is targeted at hosting up to 100 virtual machine instances simultaneously on a modern server. The virtualization approach taken by Xen is extremely efficient: we allow operating systems such as Linux and Windows XP to be hosted simultaneously for a negligible performance overhead --- at most a few percent compared with the unvirtualized case. We considerably outperform competing commercial and freely available solutions in a range of microbenchmarks and system-wide tests.

Data center virtualization allows cost-effective server consolidation which can increase system throughput and reduce power consumption. Resource management of virtualized servers is an important and challenging task, especially when dealing with fluctuating workloads and complex multi-tier server applications. Recent results in control theory-based resource management have shown the potential benefits of adjusting allocations to match changing workloads.This paper presents a new resource management scheme that integrates the Kalman filter into feedback controllers to dynamically allocate CPU resources to virtual machines hosting server applications. The novelty of our approach is the use of the Kalman filter-the optimal filtering technique for state estimation in the sum of squares sense-to track the CPU utilizations and update the allocations accordingly. Our basic controllers continuously detect and self-adapt to unforeseen workload intensity changes.Our more advanced controller self-configures itself to any workload condition without any a priori information. Indicatively, it results in within 4.8% of the performance of workload-aware controllers under high intensity workload changes, and performs equally well under medium intensity traffic. In addition, our controllers are enhanced to deal with multi-tier server applications: by using the pair-wise resource coupling between application components, they provide a 3% on average server performance improvement when facing large unexpected workload increases when compared to controllers with no such resource-coupling mechanism. We evaluate our techniques by controlling a 3-tier Rubis benchmark web site deployed on a prototype Xen-virtualized cluster.

Virtual machine monitors (VMMs) have been hailed as the basis for an increasing number of reliable or trusted computing systems. The Xen VMM is a relatively small piece of software -a hypervisor -that runs at a lower level than a conventional operating system in order to provide isolation between virtual machines: its size is offered as an argument for its trustworthiness. However, the management of a Xen-based system requires a privileged, fullblown operating system to be included in the trusted computing base (TCB).In this paper, we introduce our work to disaggregate the management virtual machine in a Xen-based system. We begin by analysing the Xen architecture and explaining why the status quo results in a large TCB. We then describe our implementation, which moves the domain builder, the most important privileged component, into a minimal trusted compartment. We illustrate how this approach may be used to implement "trusted virtualisation" and improve the security of virtual TPM implementations. Finally, we evaluate our approach in terms of the reduction in TCB size, and by performing a security analysis of the disaggregated system.

This paper investigates the effect of mobile phone screen size (1.65 inches - 2.75 inches) on video based learning. It first examines the educational benefits of video as a teaching medium and surveys the usage and issues related with video based learning. After which, it investigates the value of video for mobile learning. It reports on an empirical investigation that studied the effect that screen-size has on video-based m-learning. Findings indicate that regardless of the screen size of a mobile phone, students tended to have a positive overall opinion of m-learning and watching the video significantly increased their knowledge of the subject area. However, if an m-learning environment that relies heavily on video based material is displayed on a mobile device with a small screen, such as an average mobile phone, then the effectiveness of the learning experience may be inhibited. Paper identifies the underlying reasons why mobile phone screen size may be a problem for video based m-learning. The implications of this finding are discussed.

We present the design of Mnemosyne 1 , a peer-to-peer steganographic storage service. Mnemosyne provides a high level of privacy and plausible deniability by using a large amount of shared distributed storage to hide data. Blocks are dispersed by secure hashing, and loss codes used for resiliency. We discuss the design of the system, and the challenges posed by traffic analysis.

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