The development of UNIX
Time division system is a UNIX. The first UNIX system came out in 1970. Previously, there was only an operating system for batch jobs, which was too slow for users who needed an immediate response. In the late 1960s, both Kenneth Thompson and Dennis Ritchie participated in the design of interactive time-sharing system MULTICS, which was developed by CTSS. These two systems have had a significant impact in the development of the operating system. On this basis, in the process of refining and developing the existing technology at that time, K. Thompson developed UNIX system on small computer in 1969, and then put it into operation in 1970.
In 1973, Dennis Ritchie developed c language, which was used to rewrite UNIX written in assembly language, resulting in UNIX version v. In 1974, Kenneth Thompson and Dennis Ritchie published “the UNIX time sharing system” on the communication of ACM, and officially disclosed the UNIX system to the outside world.
At that time, PDP-11 series minicomputers had been widely used all over the world. As soon as UNIX system was developed, it was widely equipped on PDP-11 series computers in American universities, thus creating material conditions for the wide application of UNIX.
UNIX version VI was published in 1978 and then used in VAX-11 super Minicomputer in 1979. After that, various new versions appeared constantly. At & T UNIX System II and UNIX System V were published in 1981 and 1983 respectively. The University of California at Berkeley has also published UNIX versions bsd4.1, bsd4.2 and bsd4.3.
Nowadays, the users of UNIX system are increasing day by day, and the application scope is also expanding day by day. No matter in various types of microcomputers, minicomputers, medium and large computers, as well as in computer workstations and even personal computers, many have been equipped with UNIX system. Not only the new models are equipped with UNIX system, but also some manufacturers with a long history are competing to equip the original models with UNIX system, so as to open up the market and strive for the market.
The birth of UNIX
In UNIX, signal is a very important software interrupt. When will signal be generated
1. Hardware exception (e.g. divide by 0)
2. Software conditions (such as alarm timer timeout)
3. The terminal generates the signal
4. Call the kill function
Characteristics of UNIX
UNIX system plays an important role in the history of computer operating system. It has made meticulous, careful and selective inheritance and transformation of the existing technology, and has developed in the overall design concept of the operating system, which makes it so successful. The main characteristics of UNIX system are as follows
(1) UNIX system is divided into kernel program and shell program in structure, and they are combined into a whole. The core part undertakes the functions of each module in the system, namely processor and process management, storage management, device management and file system. The core program is well-designed, concise and capable. It only needs to occupy a small space and stay in memory to ensure the efficient operation of the system. The peripheral part includes the user interface, system utility and application program of the system. The user uses the computer through the peripheral program. ［2］
(2) UNIX system provides a good user interface, with the characteristics of easy to use, complete functions, clear and flexible, easy to expand and modify. UNIX system is used in two forms: one is the operation command, that is, shell language, which is the interface that users can interact with the system through the terminal; the other is the user program oriented interface, which provides services to users not only in assembly language, but also in C language.
(3) The file system of UNIX system is a tree structure. It is composed of a basic file system and several detachable sub file systems, which can not only expand the file storage space, but also be conducive to security and confidentiality.
(4) UNIX system processes files, file directories and devices in a unified way. It takes the file as a character stream without any records for sequential or random access, and makes the file, file directory and device have the same syntax and semantics and the same protection mechanism. This not only simplifies the system design, but also facilitates the use of users.
(5) UNIX system contains rich language processing programs, utility programs and tool software for developing software, which provides users with a fairly complete software development environment.
(6) Most programs in UNIX system are programmed in C language, and only about 5% programs are programmed in assembly language. C language is a high-level programming language, which makes UNIX system easy to understand, modify and expand, and has very good portability.
(7) UNIX system also provides a simple communication function between processes.