I. Why do I have an operating systemwithout the operating system, the computer can also run, but the programmer to understand the various details of the bottom of the computer, and the operating system intelligently encapsulated the bottom of these complex operations, through to the programmer to open a one-to-one interface, to finally enable us to implement the operating process of the underlying hardware. share the use of hardware resources, and specify some specifications for the user so that different users can share the use of the Hardware. the operating system is designed to allow us to better use hardware resources of various hardware resources. Two. the operating system location operating system is located between the Computer's underlying hardware and application software, is essentially a software, consisting of two Parts. 1. Operating system kernel (running in kernel state, operation on Hardware) 2. The interface of the system call (running in the user state, providing the calling interface for the Application) three. operating system Functions 1. provides the system invocation interface for the application Programmer. Once the application programmer has these interfaces, it is no longer necessary to consider the details of the hardware, and the operation of the hardware can be done with a simple call. 2. Because the software is all sharing the same set of hardware resources, and the operating system can manage hardware resources, so that different software to the hardware Resources disorderly competition request becomes orderly, that is, multiplexing technology four. the development of the operating system1. First generation computer (1945-1955): vacuum tube and punch cardWilliam Mauchley of the University of Pennsylvania and his students J.presper Eckert built ENIAC. These machines are binary, some use vacuum tubes, some are programmable, but are very primitive, it takes a few seconds to complete the simplest operation. the machines of this period require a team to design, manufacture, program, operate, and maintain each MACHINE. Programming Using machine language, the basic function is controlled by a hard connection on the Board. At this time in the early stages of computer development, no programming language appeared, the operating system is unheard of! 2. Second generation computer (1955-1965): transistor and batch processing systemat this time the computer is more and more reliable, has come out from the research institute, entered the commercial Application. however, This period of the computer to complete a variety of scientific calculations, requires specialized operator maintenance, and needs to be programmed for each calculation Task. The second generation of computers is mainly used for scientific and engineering calculations. Using FORTRAN and assembly languageWrite the Program. The concept of the original operating system appeared, but still need People's participation, by putting a bunch of people input into the computer processing, together print out the results, returned to the Programmer. 3. Third generation computer (1965-1980): IC chip and multi-channel programIn the early 60, computer vendors were divided into two computer series according to different applications, a word-oriented, scientific computing; a character-oriented, commercial Application. With the deepening of computer application, the requirements for the unification of two kinds of applications appear. At this time IBM tried to solve this problem by introducing system/360, which was the predecessor of the server, and with this plan, IBM organized the development of the OS/360 operating system, then the complex requirements, and then the software engineering level was low so that os/ 360 of the development effort has been the scariest "software development quagmire" since History.. Although the development plan failed, but this desire has become the goal of computer Manufacturers. At this point, MIT, Bell Labs and General Electricdecided to develop a "public computer service system"----MULTICS, a machine that wanted to support hundreds of tick users at the same time. As a result, the plan was more difficult to develop than everyone expected, and the system ended in Failure. however, Multics's ideas are a lot of hints for later operating Systems. In the 60 's, a computer scientist, Ken Thompson, who worked at Bell Labs in multics, developed a simplified, single-user version of Multics on an unmanned PDP-7 machine. Later lead to uNIX's Birth. Currently UNIXdominate the minicomputer, workstations, and other Markets. is one of the most influential operating systems to date, and Linux is a derivative of Unix systems. 4. Fourth generation computer (1980-present): pcpersonal computers are booming and prices are falling. Because of the characteristics of the UNIX system, which makes it less suitable for running on a personal computer, a new operating system is Needed. At this historic juncture, when IBM underestimated the PC market and did not use the greatest power to compete for the market, Intel took the opportunity to enter and become the boss of Today's Microprocessors. At the same time, Microsoft's president, who is good at seizing the opportunity, entered the field in time, using the purchased cp/m to become ms-dos, with Windows becoming the overlord of the PC operating System. Five. Multi-channel technology: multiplexing, the operating system can handle requests from multiple, multi-channel shared resources initiated by several programs. There are two ways to achieve This. 1. The reuse of time in different programs or the user takes turns using the same resource, that is, the resource is reused in Time. We usually see multiple tasks in parallel is actually the operating system to different programs on the CPU occupy a different time slice, take turns occupy, so in the User's opinion, the program seems to be parallel. In fact, the duration of this resource allocation and preemption priority issues are handled by the operating System. 2. Reuse of space each program obtains a small portion of the larger resources, reducing the time to wait for a queue, or space reuse. Multiple programs go into memory, and the hardware provides protection to split their memory and is controlled by the operating system, which improves a lot of efficiency. Six. What are Internet protocols and why Internet Protocol Internet Protocol defines the rules, standards, and conventions for data exchange in a computer network, i.e. how computers access the internet, and the standards of Communication. To complete the communication between two computers, it is necessary to follow certain standards and rules, so there is a unified standard of Internet Protocol to standardize such communication process. Seven. OSI five Layer Model 1. Physical Layer Two computers to complete communication, there must be a physical layer Involved. Send high and low voltage signals based on electrical characteristics, such as sending high and low levels on a twisted pair to represent different binary Information. 2. The data link layer defines the way in which the electrical signals are grouped, that is, the data is encapsulated as a data frame. In the Ethernet protocol, the data has the frame head and the data two parts, the frame header contains the Mac address, the MAC address is unique, unique Identification. 3. The network layer solves the communication between multiple lans, and the IP is used to differentiate the different lans. Now the commonly used protocol is the IPV4 protocol, after the IP address and subnet mask to do and operation, the result is the same, in order to determine the two IP is the same subnet. IP packets are also classified as headers and data, and the headers contain information such as IP addresses. 4. Transport Layer After we find the computer we want to access through Mac and ip, we need to identify the application on the host through the port, and the Transport layer establishes port-to-port Communication. Port Range 0-65535 (0-1023 system-occupied PortsThe protocol for this layer is stable for TCP and udp,tcp, but the transmission efficiency is low, while UDP is the Opposite. 5. Application-level users are working in the application layer, but to follow the various forms of data, you can make a common protocol (such as http,ftp, etc.), or it can be your own defined communication Protocol. Eight. User Access Process 1. This machine obtains the IP address, subnet mask, gateway IP and DNS IP2. open the browser, enter the URL you want to access 3.DNS resolution, Step-by-Step inquiry to resolve the last IP address to access the URL 4.HTTP protocol, plus embedded http-compliant header data 5.TCP protocol, TCP packets need to To set the port number for both Sides. The 6.IP protocol, the TCP packet embedded in the IP packet, contains the IP address of both parties, 7. Ethernet protocol, IP packets embedded in the Ethernet packet, containing both Mac Addresses. 8. Server-side response, through multiple gateways, the server that wants to access the URL receives the Ethernet packet, according to the IP header ordinal, The complete TCP packet, reads the HTTP request, makes the HTTP response, then sends back with the TCP protocol, the native receives the HTTP response, can display the webpage, Complete the Communication.
Python road-operating system & Network Fundamentals
