Книга: Distributed operating systems

10.1.2. Goals of DCE

10.1.2. Goals of DCE

The primary goal of DCE is to provide a coherent, seamless environment that can serve as a platform for running distributed applications. Unlike Amoeba, Mach, and Chorus, this environment is built on top of existing operating systems, initially UNIX, but later it was ported to VMS, WINDOWS, and OS/2. The idea is that the customer can take a collection of existing machines, add the DCE software, and then be able to run distributed applications, all without disturbing existing (nondistributed) applications. Although most of the DCE package runs in user space, in some configurations a piece (part of the distributed file system) must be added to the kernel. OSF itself only sells source code, which vendors integrate into their systems. For simplicity, in this chapter we will concentrate primarily on DEC on top of UNIX.

The environment offered by DCE consists of a large number of tools and services, plus an infrastructure for them to operate in. The tools and services have been chosen so that they work together in an integrated way and make it easier to develop distributed applications. For example, DCE provides tools that make it easier to write applications that have high availability. As another example, DCE provides a mechanism for synchronizing clocks on different machines, to yield a global notion of time.

DCE runs on many different kinds of computers, operating systems, and networks. Consequently, application developers can easily produce portable software that runs on a variety of platforms, amortizing development costs and increasing the potential market size.

The distributed system on which a DCE application runs can be a heterogeneous system, consisting of computers from multiple vendors, each of which has its own local operating system. The layer of DCE software on top of the operating system hides the differences, automatically doing conversions between data types when necessary. All of this is transparent to the application programmer.

As a consequence of all of the above, DCE makes it easier to write applications in which multiple users at multiple sites work together, collaborating on some project by sharing hardware and software resources. Security is an important part of any such arrangement, so DCE provides extensive tools for authentication and protection.

Finally, DCE has been designed to interwork with existing standards in a number of areas. For example, a group of DCE machines can communicate with each other and with the outside world using either TCP/IP or the OSI protocols, and resources can be located either using the DNS or X.500 naming systems. The POSIX standards are also used.

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