The Logical Disk (LD) defines a new interface to disk storage that separates file management and disk management by using logical block numbers and block lists. The LD interface is designed to support multiple file systems and to allow multiple implementations, both of which are important given the increasing use of kernels that support multiple operating system personalities. A log-structured implementation of LD (LLD) demonstrates that LD can be implemented efficiently. LLD adds about 5% to 10% to the purchase cost of a disk for the main memory it requires. Combining LLD with an existing file system results in a log-structured file system that exhibits the same performance characteristics as the Sprite log-structured file system.

This article explores memory sharing and protection support in Opal, a single-address-space operating system designed for wide-address (64-bit) architectures. Opal threads execute within protection domains in a single shared virtual address space. Sharing is simplified, because addresses are context independent. There is no loss of protection, because addressability and access are independent; the right to access a segment is determined by the protection domain in which a thread executes. This model enables beneficial code- and data-sharing patterns that are currently prohibitive, due in part to the inherent restrictions of multiple address spaces, and in part to Unix programming style. We have designed and implemented an Opal prototype using the Mach 3.0 microkernel as a base. Our implementation demonstrates how a single-address-space structure can be supported alongside of other environments on a modern microkernel operating system, using modern wide-address architectures. This article justifies the opal model and its goals for sharing and protection, presents the system and its abstractions, describes the prototype implementation,

The appearance of 64-bit address space architectures, such as the DEC Alpha, HP PA-RISC, and MIPS R4000, signals a radical shift in the amount of address space available to operating systems and applications. This shift provides the opportunity to reexamine fundamental operating system structure specifically, to change the way that operating systems use address space. This paper

To provide modularity and performance, operating system kernels should have only minimal embedded functionality. Today's operating systems are large, inefficient and, most importantly, inflexible. In our view, most operating system performance and flexibility problems can be eliminated simply by pushing the operating system interface lower. Our goal is to put abstractions traditionally implemented by the kernel out into user-space, where user-level libraries and servers abstract the exposed hardware resources. To achieve this goal, we have defined a new operating system structure, exokernel, that safely exports the resources defined by the underlying hardware. To enable applications to benefit from full hardware functionality and performance, they are allowed to download additions to the supervisor-mode execution environment. To guarantee that these extensions are safe, techniques such as code inspection, inlined cross-domain procedure calls, and secure languages are used. To test and ...

We describe the use of a reconfigurable board to obtain information on the performance that can be expected on particular systems. Our goal is to use the reconfigurability of the board's interface to test a system and discover not only the maximum bandwidth and best latency attainable, but also the way to reliably achieve these figures. The board we present uses the now widespread PCI bus. PCI is sufficiently complex, and its implementations sufficiently varied, that it is impossible to guess the performance that can be obtained by a specific board on a specific computer with the only technical characteristics of the two in hand. We observe astonishing performance differences between almost identical systems and comparable figures between small PCs and big servers. Our performance tests can be an end in themselves, however they also serve to demonstrate the value of a reconfigurable bus interface. With the same board, we can test and choose a system, make informed architectural decisio...

. Forthcoming massively parallel systems are distributed memory architectures. They consist of several hundreds to thousands of autonomous processing nodes interconnected by a highspeed network. A major challenge in operating system design for massively parallel architectures is to design a structure that reduces system bootstrap time, avoids bottlenecks in serving system calls, promotes fault tolerance, is dynamically alterable, and application-oriented. In addition to that, system-wide message passing is demanded to be of very low latency and very high efficiency. State of the art parallel operating systems design must obey the maxim not to punish an application by unneeded system functions. This requires to design a parallel operating system as a family of program modules, with parallel applications being an integral part of that family, and motivates object orientation to achieve an efficient implementation. 1 Introduction Compared to the classical operating systems area...

The modern operating system is caught between the rapid evolution of application requirements and the equally rapid evolution of hardware platforms. The ability for the system to adapt to meet these demands is increasingly paramount, yet the mechanisms provided, by most commercial systems, to achieve these goals are either too restrictive or too slow to be viable. Recent research work has concentrated on various solutions to this problem, usually through some form of extensible kernel, where additional services may be added as necessary. In this paper, we examine the needs of an extensible kernel in the context of Angel, a single address space operating system. We found that by sensible design of primitive kernel services, and the advantages obtained by adopting a single address space, an operating system can be made flexible, extensible and secure without compromising performance. 1 Introduction Operating systems research has endeavoured over the years to separate many of the kernel'...