The future of software engineering isn't what it used to be. The nature of the software we write, the reasons we write it and the way we write it and maintain it have changed rapidly and dramatically over the last few years. And software development is likely change even faster over the next decade. In this talk I will reflect on how commercial software has evolved and what it might look like in the not-to-distant future.

We have improved the performance of the Mach 3.0 operating system by redesigning its internal thread and interprocess communication facilities to use continuations as the basis for control transfer. Compared to previous versions of Mach 3.0, our new system consumes 85% less space per thread. Cross-address space remote procedure calls execute 14% faster. Exception handling runs over 60% faster.In addition to improving system performance, we have used continuations to generalize many control transfer optimizations that are common to operating systems, and have recast those optimizations in terms of a single implementation methodology. This paper describes our experiences with using continuations in the Mach operating system.

We discuss the translation lookaside buffer (TLB) consistency problem for multiprocessors, and introduce the Mach shootdown algorithm for maintaining TLB consistency in software. This algorithm has been implemented on several multiprocessors, and is in regular production use. Performance evaluations establish the basic costs of the algorithm and show that it has minimal impact on application performance. As a result, TLB consistency does not pose an insurmountable obstacle to multiprocessors with several hundred processors. We also discuss hardware support options for TLB consistency ranging from a minor interrupt structure modification to complete hardware implementations. Features are identified in current hardware that compound the TLB consistency problem; removal or correction of these features can simplify and/or reduce the overhead of maintaining TLB consistency in software.

The authors describe the design, implementation, and evaluation of the Mach virtual-memory management system. The Mach virtual-memory system exhibits architecture independence, multiprocessor and distributed system support, and advanced functionality. The performance of this virtual-memory system is shown to often exceed that of commercially developed memory management systems targeted at specific hardware architectures.>

This paper describes the design and implementation of virtual memory management within the CMU Mach Operating System and the experiences gained by the Mach kernel group in porting that system to a variety of architectures. As of this writing, Mach runs on more than half a dozen uniprocessors and multiprocessors including the VAX family of uniprocessors and multiprocessors, the IBM RT PC, the SUN 3, the Encore MultiMax, the Sequent Balance 21000 and several experimental computers. Although these systems vary considerably in the kind of hardware support for memory management they provide, the machine-dependent portion of Mach virtual memory consists of a single code module and its related header file. This separation of software memory management from hardware support has been accomplished without sacrificing system performance. In addition to improving portability, it makes possible a relatively unbiased examination of the pros and cons of various hardware memory management schemes, especially as they apply to the support of multiprocessors.

Code to implement network protocols can be either inside the kernel of an operating system or in user-level processes. Kernel-resident code is hard to develop, debug, and maintain, but user-level implementations typically incur significant overhead and perform poorly.

Mach is a multiprocessor operating system being implemented at Carnegie-Mellon University. An important component of the Mach design is the use of memory objects which can be managed either by the kernel or by user programs through a message interface. This feature allows applications such as transaction management systems to participate in decisions regarding secondary storage management and page replacement.

Mach, a multiprocessor operating system kernel providing capability-based interprocess communication, and Matchmaker, a language for specifying and automating the generation of multi-lingual interprocess communication interfaces, are presented. Their usage together providing a heterogeneous, distributed, object-oriented programming environment is described. Performance and usage statistics are presented. Comparisons are made between the Mach/Matchmaker environment and other related systems. Possible future directions are examined.

The Mach operating system supports secure local communication within one node of a distributed system by providing protected communication abstraction can be extended over a network by Network Server tasks. The network servers effectively act as local representatives for remote tasks by implementing an abstraction of Network Ports. To extend the security of the port-based communication abstraction into the network environment, the network servers must protect both the messages sent over the network to network ports and the access rights to network ports. This paper describes in detail the protocols used by the network servers to support security.

The integration of virtual memory management and interprocess communication in the Accent network operating system kernel is examined. The design and implementation of the Accent memory management system is discussed and its performance, both on a series of message-oriented benchmarks and in normal operation, is analyzed in detail.

Matchmaker, a language used to specify and automate the generation of interprocess communication interfaces, is presented. The process of and reasons for the evolution of Matchmaker are described. Performance and usage statistics are presented. Comparisons are made between Matchmaker and other related systems. Possible future directions are examined.

No abstract available.

As part of our research in the Archons [Jensen 82] project on decentralized computers, we have developed a relational model of data consistency to replace the conventional serialization model for reasoning about the relationships among distributed system data objects in general and state variables in particular. We not only permit but encourage such relationships to be probabilistic, in the interest of efficiency. This model leads to a new formulation of co-operating processes, and thence to the notion of co-operating transactions: co-operating processes whose actions are made atomic for the sake of reliability. We believe that co-operating processes are valuable in a computer network, but essential in a decentralized computer [Jensen 82] where the conceptually singular but physically dispersed global operating system requires a transaction facility in the kernel [Jensen 80]. These ideas are illustrated by examples from our initial experience in applying the model to the Accent network operating system and other system software of the Spice personal computing network. This document is intended to be an overview of the synchronization effort in the Archons project, and future publications will elaborate on many of the individual points touched on here.

Accent is a communication oriented operating system kernel being built at Carnegie-Mellon University to support the distributed personal computing project, Spice, and the development of a fault-tolerant distributed sensor network (DSN). Accent is built around a single, powerful abstraction of communication between processes, with all kernel functions, such as device access and virtual memory management accessible through messages and distributable throughout a network. In this paper, specific attention is given to system supplied facilities which support transparent network access and fault-tolerant behavior. Many of these facilities are already being provided under a modified version of VAX/UNIX. The Accent system itself is currently being implemented on the Three Rivers Corp. PERQ.

Rochester's Intelligent Gateway provides its users with the facilities for communicating simultaneously with a large number of processes spread out among various computer systems. We have adopted the philosophy that the user should be able to manage any number of concurrent tasks or jobs, viewing their output on his display device as he desires. To achieve this goal the Virtual Terminal Management System (VTMS) converts a single physical terminal into multiple virtual terminals, each of which may be written to or queried for user input. VTMS extends the features of the physical terminal by providing extensive editing facilities, the capacity to maintain all output In disk-based data structures, and sophisticated mechanisms for the management of screen space. Virtual terminals are device-independent; the specific characteristics of the physical terminal are known only to the lowest-level I/O handlers for that device. VTMS Is currently running on a network of six minicomputers supporting various text and raster-graphics displays.

Rochester's Intelligent Gateway (RIG) system provides convenient access to a wide range of computing facilities. The system includes five large minicomputers in a very fast internal network, disk and tape storage, a printer/plotter and a number of display terminals. These are connected to larger campus machines (IBM 360/65 and DEC KL10) and to the ARPANET. The operating system and other software support for such a system present some interesting design problems. This paper contains a high-level technical discussion of the software designs, many of which will be treated in more detail in subsequent reports.