UNIX时间共享系统：开创性的论文解析

需积分: 10 96 浏览量更新于2024-07-29 1 收藏 56KB PDF 举报

"这篇论文是关于UNIX时间共享系统的，由D.M. Ritchie和K. Thompson撰写，他们是UNIX操作系统的缔造者。论文强调了UNIX在操作系统领域的独特性和先进性，适合黑客定期阅读以深入理解其设计理念和技术细节。" 这篇论文详细介绍了UNIX系统的一些核心特性，这些特性即使在当时较大的操作系统中也并不多见。以下是一些主要知识点： 1. 分层文件系统：UNIX引入了一种层次结构的文件系统，允许挂载和卸载卷，这极大地提高了灵活性和存储管理能力。这种设计使得用户可以方便地组织和访问数据，同时支持多个存储设备。 2. 兼容的文件、设备和进程间I/O：在UNIX系统中，文件、设备和进程间的输入输出操作具有兼容性，这意味着它们可以使用相同的基本接口进行通信，简化了程序开发和系统维护。 3. 异步进程启动：UNIX允许用户并行执行多个任务，进程可以独立于用户的交互运行，提高了系统的效率和响应性。 4. 用户可选择的系统命令语言：用户可以根据自己的偏好选择不同的系统命令语言，增强了用户体验和个性化定制。 5. 多样化的子系统和编程语言：超过100个子系统，包括多种编程语言，如C、 awk、sed等，这为开发者提供了丰富的工具和选择，促进了软件开发的繁荣。 6. 高度的可移植性：UNIX的设计使得它可以在不同硬件平台上运行，这在当时是非常先进的，为后来的操作系统设计树立了榜样。论文主要探讨了文件系统和用户命令接口的性质和实现。文件系统部分可能涵盖了文件的创建、删除、权限管理、链接以及I/O操作等方面，而用户命令接口则可能涉及shell、脚本编程和系统调用等。早期的UNIX系统经历了四个版本的发展，从最初的PDP-7和PDP-9到后来的多用户、多任务的PDP-11系列。随着硬件的进步，UNIX系统不断优化和完善，第三版更是引入了多编程功能，能够在PDP-11系列的不同型号上运行。这篇论文对于理解UNIX系统的历史、设计哲学和实现技术至关重要，对于计算机科学家、系统管理员和程序员来说，都是一份宝贵的参考资料。

- 3 -

contents of directories. However, anyone with appropriate permission may read a directory just like any

other file.

The system maintains several directories for its own use. One of these is the root directory. All files

in the system can be found by tracing a path through a chain of directories until the desired file is reached.

The starting point for such searches is often the root. Other system directories contain all the programs

provided for general use; that is, all the commands. As will be seen, however, it is by no means necessary

that a program reside in one of these directories for it to be executed.

Files are named by sequences of 14 or fewer characters. When the name of a file is specified to the

system, it may be in the form of a path name, which is a sequence of directory names separated by slashes,

‘‘/’’, and ending in a file name. If the sequence begins with a slash, the search begins in the root directory.

The name /alpha/beta/gamma causes the system to search the root for directory alpha, then to search

alpha for beta, finally to find gamma in beta. gamma may be an ordinary file, a directory, or a special

file. As a limiting case, the name ‘‘/’’ refers to the root itself.

A path name not starting with ‘‘/’’ causes the system to begin the search in the user’s current direc-

tory. Thus, the name alpha/beta specifies the file named beta in subdirectory alpha of the current direc-

tory. The simplest kind of name, for example, alpha, refers to a file that itself is found in the current direc-

tory. As another limiting case, the null file name refers to the current directory.

The same non-directory file may appear in several directories under possibly different names. This

feature is called linking; a directory entry for a file is sometimes called a link. The Unix system differs

from other systems in which linking is permitted in that all links to a file have equal status. That is, a file

does not exist within a particular directory; the directory entry for a file consists merely of its name and a

pointer to the information actually describing the file. Thus a file exists independently of any directory

entry, although in practice a file is made to disappear along with the last link to it.

Each directory always has at least two entries. The name ‘‘.’’ in each directory refers to the direc-

tory itself. Thus a program may read the current directory under the name ‘‘. ’’ without knowing its com-

plete path name. The name ‘‘..’’ by convention refers to the parent of the directory in which it appears,

that is, to the directory in which it was created.

The directory structure is constrained to have the form of a rooted tree. Except for the special entries

‘‘ .’’ and ‘‘ ..’’, each directory must appear as an entry in exactly one other directory, which is its parent.

The reason for this is to simplify the writing of programs that visit subtrees of the directory structure, and

more important, to avoid the separation of portions of the hierarchy. If arbitrary links to directories were

permitted, it would be quite difficult to detect when the last connection from the root to a directory was sev-

ered.

3.3 Special files

Special files constitute the most unusual feature of the Unix file system. Each supported I/O device

is associated with at least one such file. Special files are read and written just like ordinary disk files, but

requests to read or write result in activation of the associated device. An entry for each special file resides

in directory /dev, although a link may be made to one of these files just as it may to an ordinary file. Thus,

for example, to write on a magnetic tape one may write on the file /dev/mt. Special files exist for each

communication line, each disk, each tape drive, and for physical main memory. Of course, the active disks

and the memory special file are protected from indiscriminate access.

There is a threefold advantage in treating I/O devices this way: file and device I/O are as similar as

possible; file and device names have the same syntax and meaning, so that a program expecting a file name

as a parameter can be passed a device name; finally, special files are subject to the same protection mecha-

nism as regular files.

3.4 Removable file systems

Although the root of the file system is always stored on the same device, it is not necessary that the

entire file system hierarchy reside on this device. There is a mount system request with two arguments: the

name of an existing ordinary file, and the name of a special file whose associated storage volume (e.g., a

disk pack) should have the structure of an independent file system containing its own directory hierarchy.

剩余14页未读，继续阅读

jiankangshiye

粉丝: 73
资源: 109

UNIX时间共享系统：开创性的论文解析

ACM论文投稿模板指南

ACMART论文模板：高效排版ACM系列论文

ACM论文LaTeX类：设计与使用指南

unix经典论文

UNIX PROGRAMMER’S MANUAL(UNIX编程手册)

浙江大学ACM题解/ZJU 题型分类

UNIX操作系统发展史.pdf

UNIX操作系统发展史.docx

UNIX操作系统发展史(20211115220649).pdf

ZJU_ACM_All_Anwer 搞编程的都知道的浙江大学Ａ 题库．本书 集了所有经 Ｚ 题解集，集合并附 Mathimaticsumerical algorithms 数值算法

最新资源

ZJU_ACM_All_Anwer 搞编程的都知道的浙江大学Ａ题库．本书集了所有经Ｚ题解集，集合并附 Mathimaticsumerical algorithms 数值算法