VB抽奖管理系统毕业论文(任务书+致谢+英文文献翻译)
The Engineering Workstation
Workstations fit somewhere between PCs and large minicomputer in terms of raw performance; although as both PCs and workstations get more powerful, the performance distinctions between the there groups are more difficult to make. Engineering Workstations do have several advantages over both PCs and traditional time-sharing or minicomputer technology, however. Workstation generally have more powerful CPUs and can support more main memory than PCs, although the latter overlap with low-end workstations in power. Workstations, unlike PCs, offer multitasking, multitasking operating systems as a standard feature. OS/2 and UNIX are available for PCs, especially for those based on the Intel 80386. However, the dominant operating system for PCs is still MS-DOS.
Multitasking systems have several advantages over single-tasking systems. First, the user can run more than a single program at a time , transparent to the application. Desk accessories and RAM-resident programs on PCs give the user some primitive multitasking capability, sufficient to run background print spoolers and the like . However, they may not be transparent to application program, and they do not offer significant features like interprocess communication and support for multiple, simultaneous users.
Perhaps more important for today’s engineering applications is the lack of large physical and virtual memories on PCs. Virtual memory is important for large applications, many of which simply cannot be run entirely in physical memory because the data sets are too large, Without virtual memory, a simple task like editing a large file becomes tedious or even impossible to perform. In addition, many applications are more complex because they must buffer data or use overlays to page different parts of the application in and out of physical memory.
Finally, the user interface of most workstations is more sophisticated than that on most PCs. The one notable exception is that of the Apple Macintosh. The computer’s user interface and the programming interface to it determine how sophisticated the application’s program interfaces can be. Powerful development tools allow programmers to create intuitive user interfaces for complex applications.
While workstations are typically more powerful than PCs, that is generally not the case when they are compared with modern minicomputers, such as those of the VAX-8oooseries by Digital Equipment Corporation(DEC). They do have several advantages over minicomputers, however. Engineering workstations generally provide more CPU power per user, a better price-performance ratio, and more predictable response times than minicomputers, because the CPU is usually devoted to a single user. Workstations often have the same user-interface advantages over minicomputers that they have over most PCs. With the advent of the X Window System and inexpensive terminals that support the X protocol, this advantage is disappearing.Problems with Networked Systems
Although workstations are giving engineers new-found computer power and display capabilities, all is not perfect. The problems become readily apparent to users and system administrators at sites with more than a handful of workstations. The Complexity of the operating systems on workstations approaches or exceeds that of minicomputer operating systems of just a few years ago. With little or no software available to automate critical tasks such as disk backup, software installation and update, network management, or account management, the administration of such a system can become a nightmare. Distributed file systems can create unexpected dependencies on many machines on a local area network. When a file server goes down, many machines(and their user)may be affected. When files are used to communicate between processes on different machines, directory caching may create inconsistencies in the appearance of the global file system on the two machines as well.
On top of the problems inherent in managing distributed systems are software licensing costs, which for many organizations have skyrocketed because most software packages for workstations are still licensed as if they were for minicomputer and mainframes. Some organizations are beginning to address the problems of administering large number of machines and software licensing but few solutions are today.

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