Introduction to Computer Systems
1. A brief history of computer development
1.1 The concept of
computer A computer is a machine that can store programs and data and execute programs automatically. A tool for conveying information.
1.2 The development history of
computer 1.2.1 The generation of computer
In 1822, the British Charles Babbage proposed the concept of "automatic computer". In 1834, the difference engine and analysis engine he designed already possess the basic components of modern computers.
1.2.2 The world's first electronic computer
came out at the University of Pennsylvania in February 1946, weighing 30 tons, using 18,000 tubes, 70,000 resistors, 10,000 capacitors, 150KW power consumption, and 5,000 operations per second 
1.2.3 According to the main components used, it is divided into five generations
, the first generation (1946-1958) - electronic tube; operation speed: 5000-40000 times/second; machine language: assembly language, used for scientific computing (advanced mathematical operations)
The second generation ( 1958-1964)--transistor; operation speed: hundreds of thousands-million times per second; machine language: high-level language--vb for data processing, automatic control
third generation (1964-1970)--small and medium-scale integrated circuits ; Computing speed: millions - several million times/second; with the operating system, used for enterprise management and auxiliary design
fourth generation (1971-1990) - large-scale and ultra-large-scale integrated circuits; computing speed: several million -Hundreds of millions of times per second; with software and network, used in various fields including traditional fields (financial, government, university)
fifth-generation modern computers; information collection, storage, processing, communication and artificial intelligence AI are combined with a form Reasoning, associative, learning and interpretive abilities. His system structure will break through the traditional concept of von Neumann machines and achieve highly parallel processing. 
1.3 Volume Classification of Computers
Microcomputers and portable computers---small computers such as personal computers and PCs
---processing multi-user tasks (IBM minicomputers---price: hundreds of thousands to millions) China's Internet industry has completed the de-IOE environment ( I--IBM minicomputer O--Oracle database E--EMC storage)
mainframe---strong operation ability, but requires multiple people to process, equivalent to a cabinet size (refrigerator)
supercomputer---used for weather forecast, Nuclear test calculation, the amount of data processing is very large, and several people coordinate to complete 
1.4 computer application field
scientific computing
data processing
automatic control
computer aided system
logic relationship processing and artificial intelligence
computer network
1.5 computer development trend
Intelligence
requires computers to simulate human thinking functions and senses, have the ability to recognize sounds and images, and have the functions of reasoning and associative learning.
Networking
uses communication technology and computer technology to interconnect computers scattered in different locations, and communicate with each other according to network protocols, so that all users can share it. Purpose of software, hardware and data resources.
The giant
has a storage capacity of hundreds of megabytes or more, a computing speed of more than trillions per second, and a computer system with complete peripheral equipment. Megaization is mainly used for research and development of cutting-edge science and technology and military defense systems.
The miniaturized
computer is further developed towards the direction of high-speed integration, that is, the computer physical devices are getting smaller and smaller, and the computing speed of the computer is faster and the function is stronger.
multimedia
Multimedia computer is the product of the combination of computer technology and television audio-visual technology. It integrates various media and is widely used in entertainment, auxiliary teaching and engineering simulation.
2. Hardware basic
computer---notebook desktop
server---1U 4U---dell server (U means thickness, 1U=4.445cm) The company usually uses 1-2U 
for a computer/server which is composed of many parts, only These components work together to coordinate the work, and it is called a computer. Mainly include: motherboard, CPU, memory, hard disk, sound card, graphics card and so on.
2.1 Computer components
2.1.1 Power supply --- The heart
guarantees the power supply of the computer (servers generally provide dual power supplies)
2.1.2 Motherboard ---
All boards in the skeleton must function through the motherboard. The motherboard is based on different architecture standards and Combination of various main components and interfaces (interface types: IDE, SATA, SAS, SCSI, iSCSI) 
2.1.3 CPU (Central Processing Unit) ---
the control center of the brain responsible for computing and control, the most critical in the computer
2.1.4 CPU fan---use copper
to cool the CPU to prevent the computer from crashing and restarting
2.1.5 The motherboard chipset
is the most important component on the motherboard, responsible for Manage CPU and memory, various bus extensions and peripheral support
2.1.6 The BIOS chip
is responsible for self-checking, setting, and saving of each component after the motherboard is powered on. Only when everything is normal can the operating system be started. It records the most basic information of the computer and is the most basic bridge between software and hardware. Without it, the computer cannot work. Three common BIOS: Award, AMI, Phoenix
2.1.7 bus expansion slot
Divided into memory slots, video card slots and so on by function. All kinds of I/O interfaces: magnetic tape - floppy disk, keyboard, mouse, printer, USB (Universal Serial Bus), etc.
2.1.8 Hard disk - disk management
mass storage - LVM, RAID used in enterprises Card, especially in the server optimization scenario, the performance of the hard disk is an important factor in determining the performance of the website.
2.1.9 The memory module
is a temporary storage, which is only responsible for the transfer of computer data and cannot be permanently stored. Capacity and processing speed directly determine the speed of computer data transmission. Together with CPU and hard disk, they are called the three major parts of a computer, generally 4G, 8G, 16G
2.1.10 Other
sound cards, optical drives, graphics cards, etc.
3. Operating system and Unix System overview
3.1 What is the
definition of an operating system: an operating system is a tool or program that communicates information between users and hardware. It is the basic system software in an electronic computer system that is responsible for supporting the operating environment of applications and the operating environment of users. It is also a computer system. Core. The operating system is the interface between the user and the computer, as well as the interface between the computer hardware and other software.
Functions: including managing the hardware, software and data resources of the computer system, controlling the operation of the program, improving the man-machine interface, providing support for other application software, making all the resources of the computer system work to the maximum, providing various forms of user interface, enabling Users have a good working environment and provide necessary services and corresponding interfaces for the development of other software. In fact, the user does not need to touch the operating system. The operating system manages the computer hardware resources, and at the same time allocates resources according to the resource request of the application, such as dividing CPU time, opening up memory space, calling printers, etc.
At present, the more common operating systems on the microcomputer (PC server) are DOS, Windows, Unix, Linux, etc.
3.2 What is Unix
It is a powerful multi-user, multi-tasking operating system that supports multiple processor architectures and was first developed by Ken Thompson, Dennis Ritchie and Douglas McIlroy at AT&T's Bell Labs in 1969. After long-term development and night, it has now become the mainstream operating system. Because Unix has the characteristics of mature technology, high reliability, strong network and database functions, outstanding scalability and good openness, it can meet the actual needs of all walks of life. Enterprises, according to their own environment development, external sales
3.3 Unix development history
4. Introduction to Linux
4.1 Introduction and history of
Linux Linux is a set of Unix-like operating systems that are free to use and open source and can be freely disseminated.
Linux is known for its efficiency and flexibility. It can realize all the Unix features on the PC computer, and has the ability of multi-tasking and multi-user. Linux is freely available under the GNU Public License.
Linux is loved for two main reasons: One is that it is free software, and users can get it and its source code without paying anything. And you can make necessary modifications to it according to your own needs, use it free of charge, and spread it without constraints; another reason, with all the functions of Unix, anyone who uses Unix operating system or wants to learn Unix operating system can learn from Linux. Acquiring
4.2GNU and GPL knowledge
The main project of the Free Software Foundation (FSF) is GNU, whose goal is to build a freely distributed and portable Unix-like operating system; GNU project software includes: Emacs editing software (similar to Vim editor), gcc Compilation software, bash command interpreter and programming language, etc.;
The core idea of GPL license is to ensure the freedom to share and modify free software, and anyone has the right to obtain, modify and redistribute the source code of free software, but requires specific changes are published.
4.3 Advantages of Linux
1) The clone of the Unix system on the PC system, the imitation of the Unix kernel is built, and it is backward compatible with the Unix instruction set.
2) A complete multi-user, multi-task, and multi-process system
3) High system stability and reliability
4) Relatively High system security
5) Perfect network services: HTTP, FTP, SMTP, POP, SAMBA, SNMP, DNS, DHCP, SSH, TELNET, etc.
6) GNU open system
7) A large number of third-party free applications
8) Many industry Vendor support: IBM, ORACLE, INTEL, HP, Google, etc.
9) Complete large-scale database platforms: ORACLE, DB/2, MySQL, etc. (Internet companies are mostly Mysq; traditional industries are mostly Oracle)
10) Complete graphical user interface: GNOME, KDE --- software (graphic software)
11) Perfect development platform: C/C++ embedded, java-tomcat/resin, Perl/shell, python
4.4Linux version ( https://www.kernel.org/ )
1) Linux operating system = kernel + system software + applications
2) Linux kernel (kernel) version cat /etc/redhat-release
3) Linux distributors: Redhat, Debian, Fedora, CentOS, Ubuntu, SUSE, OpenSUSE, Hongqi, etc.
4) After Redhat 9.0, it no longer follows GPL, it is a paid product, but it is still open source (open source code)
5) Virtualization is not used much, KVM architecture uses 6.5 or 6.8 stable version, otherwise 7.3 is mainly
supported by 4.5 graphics desktop
1) X Windows system
2) GNOME
3) KDE
general production scene operation and maintenance, do not use desktop environment, Even the desktop package is not installed, except for some special software needs (such as ORACLE needs VNC)
4.6 Linux system current application field
1) IT server Linux system application (RHEL Enterprise Edition - fee; RHEL Community Edition - free)
IT The server field is mainly Linux, Unix, and Windows. Linux gradually occupies a dominant position. Linux is widely used as an enterprise-level server. Using Linux system, it can build www server, database server, proxy server (cluster server), mail server, transparent gateway and router for enterprises. And so on, reducing operating costs, at the same time high stability, high reliability and no software copyright disputes, telecommunications, finance, government, education, banking, oil and other fields are already using Linux
2) Embedded system applications
due to Linux The system is open source, powerful, reliable, stable, flexible and has great scalability. In addition, it widely supports a large number of microprocessor architectures, hardware devices, graphics support and communication protocols. In the field of Linux-based applications, from Internet equipment (routers, switches, firewalls, load balancers) to dedicated control systems (mobile phones, PDAs, various household appliances), the Linux operating system has a large application market. In particular, after several years of development, Linux has successfully entered the mainstream embedded development platform. For example, in the field of smart phones, Linux has firmly occupied a place in the development platform of smart phones after fierce competition with Windows Mobile and Symbian, forming a tripartite confrontation.
3) Application field of personal desktop system
Common applications:
Browser Internet browsing---firefox supports Firefox browser (system built-in)
office software---open office (compatible with Microsoft office)
sending and receiving emails---webmail
real-time communication---qq, msn, etc. Etc.
text editing---vim, Emacs, etc. (similar to word)
multimedia applications---cameras, printers, etc.
Although the Linux personal desktop system has been widely supported, the Linux personal desktop system is still far from the desktop market share of windows. The biggest obstacle to competition is not the Linux desktop system product itself, but the user's concept of use, operating habits and application skills, as well as the porting of software that has been developed on Windows. It will take some time before the Linux desktop system is popularized.