Shulou(Shulou.com)06/02 Report--

What is a computer?

Early mainframe computers are actually calculators. Calculators are tools that accept instructions and data inputted by users and are processed by the mathematical logic unit of the central processor CPU to generate or store useful information and display it.

So as long as there are inputs and outputs, and can calculate the input data, it is the computer.

The PC we use now generally has several components, such as mainframe, monitor, keyboard and mouse. In the mainframe, there are motherboard, CPU, memory stick, hard disk, network card, video card, sound card, fan, power supply and chassis. There are many ways to classify, but in fact, computers have only five core devices:

Arithmetic unit + register:

Function: operation and cache, cache operation speed is the fastest, and the capacity is very small, but the cost is very expensive. We have a saying that caching is king, and this is a priority as long as we can improve the CPU cache to improve the running speed. Therefore, we generally have two important parameters to measure the performance of CPU, one is the main frequency doubling of the calculator, the unit is Hz (Hertz), the other is the speed and size of the cache, the cache speed is generally fast and very small, so a little larger cache is very high for performance improvement. As a result, the capacity of both primary and secondary caches is sometimes more important than frequency.

Controller:

Control operations, such as programmable interrupt controllers, control interrupt interactions, and the reason for multitasking is this control. This and the above calculators and registers are integrated in CPU.

Memory:

The memory we often talk about actually refers to memory sticks, which is what we call random access memory (RAM), which communicates directly with CPU. So how fast our computer runs depends largely on the amount of data it can interact with CPU at the same time.

After booting, the first section of memory is for bios, followed by the OS core, which cannot be used by the application and is occupied by the system. The rest is the memory that the system can call.

Input devices: mouse, keyboard, etc.

Output devices: monitors, printers, etc.

Note that the hard disk, because it can physically store data, is sometimes both an input device and an output device. The software we run is first stored on the hard disk, and then the memory is read from it, so the faster the hard disk is, the faster the software runs.

2. The operation mode of the computer

As we all know, after we turn on the power and press to boot, the computer will start the operating system. The current process is very fast, and some can complete this operation in 3-4 seconds. But the process is actually very complicated.

Computers are hardware, and people can't talk to the hardware directly, so we have to allocate hardware resources to the software in the system through the operating system.

In fact, the operating system can not communicate directly with the hardware. To put it bluntly, the operating system is also software, which is written in a high-level language and must be translated into a binary language that can be recognized by the machine.

OK, let's talk about the process of booting. After power on, a piece of the motherboard on the computer must be powered on all the time in order to save the configured read-only memory ROM read BIOS (basic input and output system). This BIOS communicates directly with the hardware. Through this BIOS to check whether the hardware OK can work properly, can not report an error, if possible, move on to the next step. This step is called adding a little self-test.

The next step is to go to the hard drive to read the corresponding partitions that BIOS can recognize (these partitions are different in different operating systems, such as UEFI and MBR. ) this partition is called boot partition, boot partition. It contains the system boot path, boot files, basic hardware drivers and so on.

Then load the operating system kernel and self-booting software applications according to the configuration files in the boot partition. The boot process is completed step by step. All kinds of operating systems are like this.

And after our system is turned on, we have to run a piece of software. How does it work?

The computer follows the famous barrel short board theory, and its overall running speed depends on the worst-performing device in the whole machine.

Registers generally work at the same frequency as CPU. The program must follow the principle of program locality and program portability. Locality depends on time and space, and the principle of portability must be guaranteed to run in different environments.

When we click on the program to run, we first have to deal with the library, issue the execution request, and then the library communicates with the upper system call, which forwards the request to the system kernel, which communicates with the hardware, takes the data from the hard disk, and allocates hardware resources such as memory address, put the data into memory, and then allocates CPU to get the data execution. The result, layer by layer, through the hardware, kernel, library, software. Return to the user.

3. Common operating systems

The operating system is referred to as OS. There are three common types of operating systems:

Windows: this mainly refers to the windows desktop operating system produced by Microsoft Microsoft, from the early DOS to the later 95/98/2000/XP/visit/win7/win8/win8.1/win10, including some server. This kind of operating system tends to have a graphical interface, which is simple and friendly and easy to use. It is generally used in individual users or small businesses, because it is not stable enough, so large enterprises rarely use it.

Unix:Unix is a paid operating system, and it is very expensive and there are many kinds, but all of them have to be charged. For example, MAC or IOS that we now use apple are both Unix operating systems.

Linux:Linux is an open source operating system born after Unix charges, so it is a Unix-like operating system, there are many well-known distributions, widely used in enterprises, such as some famous linux operating system, such as RadHat,CentOS,Debian,Ubuntu,Minit, there are many, many, because of its open source features, so published very quickly.

OS is important to the kernel, in fact, the system kernel itself is very small, such as window nt, the reason why it is so large is because there are a lot of images and built-in applications.

OS kernel can be regarded as a kind of virtual general software, which is a special application which is responsible for allocating and managing the coordination, switching and interruption of hardware resources.

Kernel functions include:

Process management

Memory management

File system

Network function

Hardware driver

Security mechanism

If our software wants to run on the operating system, it has to go through the human-computer interface shell, and there are plenty of graphics and command lines. Then the system call is forwarded to the kernel to use hardware resources and run. Sometimes because the system call (system call) is too low-level, but also through the library, library functions to call the interface to execute. The library can only be called for execution, providing only the execution entry, the calling interface, the API advanced interface, and does not execute itself.

To put it bluntly, a library is an application that encapsulates one or more system calls into a more advanced calling interface.

4. South Bridge and North Bridge

When it comes to computers, we have to mention the FSB front-end bus. The front-end bus has two important chips, a north bridge, which is close to the CPU, and belongs to a high-speed bus, which is connected to high-speed devices such as CPU and main memory. Now the CPU has generally integrated with the north bridge. South Bridge connects slow devices, such as hard drives, USB, network cards and other peripherals.

In order to improve the running speed and access frequency of machines, some enterprises sometimes connect high-speed solid state drives directly to CPU and Beiqiao to improve the fast disk I / O, which is also a kind of hardware optimization.

5 、 Shell

Shell, also known as shell, is located in the lower layer of the kernel operating system kernel (in fact, there are system calls and libraries in the middle). It has two functions: one is to accept user instructions (to run applications), and the other is to translate user instructions or commands into machine language.

Shell, also known as human-computer interface, has a graphical interface GUI and a command-line interface CLI. Take linux as an example, the common graphical interfaces are KDE (written by C++) and Gnome (written by C). The CLI command line interface includes sh,bash,csh,zsh,ksh,tcsh and so on.

6. Password policy

Computers have different users, and the data between different users should be confidential. This requires authorization. And our most common authorization method is to use password policy.

To improve security when creating a password, it is best to follow the following policies:

1. Use at least three of the four types of uppercase letters, lowercase letters, numbers and special symbols.

two。 The number of passwords is long enough, it is generally recommended that at least 8 characters

3. Try to use irregular random characters

4. Change passwords periodically or irregularly

5. Do not use duplicate characters and used passwords

The next article will cover the basics of linux. -Yang Guang

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