linux basics
" Learning to explore the flowers must pull out their roots. " This sentence comes from a famous saying in the poems of the Tang Dynasty poet Du Mu Liugao Cao Shi and other poems. It means that learning cannot be like looking at flowers and superficial.
, But to get to the bottom and deeply understand the essential connotation. The foundation is often the most overlooked thing, but it is often the foundation that can change the goal you want to achieve!
“Learn not to explore the flowers, we must extricate ourselves” 加油，朋友！
About server classification and common brands
First of all, servers are divided into three categories. The first type: rack servers are divided into (1u 2u 3u 4u) u=1.75 inches u=4.45cm Generally, rack servers are more stable and reliable than those used by enterprises. The second type: The appearance of a blade server is similar to that of a blade. The volume is much smaller than that of a rack server, and the price is lower than that of a rack server. Several blade servers form a blade cabinet to achieve the functions required by the server. For rack servers, performance is better than rack servers. The third type: tower server, which looks similar to home desktops. Compared with desktops, there are more hard drives than desktops. There is also a type of minicomputer server that is not commonly used nowadays. This type of server is generally a private customization system. Customize system functions according to your needs. Generally, the price is relatively high compared to other services. About our common server brands are generally: Dell HP IBM.
The five components of the computer
The first part: CPU
CPU is like the human brain, responsible for controlling various data and operations.
There are two types of storage, the
first type: memory, features, faster data writing and reading data speed, higher efficiency, disadvantages, data will be lost when power is off, it is used for temporary data storage location, external storage: mechanical Hard disk: Features slow efficiency, slow data writing and reading speeds, data can be stored permanently, and data will not be lost when power is off.
Input device: It is one of the main devices for calculator and human information exchange, such as keyboard, mouse, etc.
Output device: It is the terminal device of the computer hardware system, used to receive the output display of the calculator and so on. Such as: display, etc.
The three most important cores of the five major components of a computer are: CPU, memory, hard disk. Three core relationships. First of all, the program must be in the hard disk, and the program must be run by extracting the program from the hard disk and loading it into the memory for reading. When we need to run this program, we can directly read the program instructions in the memory. carry out
The concept of buffer cache in Linux system
First of all, let me introduce (buffer) buffer, as the name implies, if you directly write data to the hard disk or write data to the disk, the speed and efficiency will be slower. How can we be efficient and fast? Then naturally we need to use the buffer in Linux to write the data we want to write into the buffer memory, which increases our writing efficiency and speed. When the buffer is accumulated to After a certain amount, the data can be sent to the hard disk for permanent storage. In the same way, when the speed of reading data is relatively slow, we can also write frequently read data in the hard disk to the cache area, and read from the cache to increase our speed efficiency.
The number of CPU architecture cores and threads. First of all, let's talk about the X86 architecture that can be divided into a complex instruction set, and a simplified instruction set. We usually say that a CPU has 2 cores and 4 threads, which means that the CPU has 2 cores, each core is equivalent to an independent CPU, and each core has 2 threads, so a 2 core CPU has a total of 4 Thread. The general formula is true 4 cores> 2 cores 4 threads> pure 2 cores.
Kernel mode and user mode, as the name implies, kernel mode: use the operating system to control the operation of the hardware. User mode: the application is running
BIOS system
Since BIos system manufacturers do not want us to modify the Bios system to install ROM read-only memory, because it can only be read, the content inside cannot be modified. How can the data of the blos system be saved? Therefore, the CMOS chip is loaded, and the CMOS chip is readable and writable. This perfectly changes the shortcomings of the data that the Bios system cannot save.
Classification of hard drives in computers
There are two main types of hard drives. The first type of mechanical hard disk, as the name suggests, is composed of mechanization, the main components are tracks, sectors, and cylinders. First, let's talk about the tracks. Track. When the disk rotates, if the head is held in one position, each head will draw a circular track on the surface of the disk. This circular track is the track. Sectors refer to the divided areas on the disk. These arcs are the sectors of the disk. Hard disk reads and writes are based on sectors. The minimum read/write unit of the hard disk is a sector=》512Bytes (byte) The minimum unit read/write of the operating system is a block->8 sector size->4k. Cylinder. Cylinder refers to the disk corresponding to all the disks contained in the middle from one cylinder to another. Ps: buffer = large truck, block of operating system = storage box, sector of hard disk = single express box, n storage boxes are stored in the large truck, and 8 express boxes are stored in each storage box. Solid State Drive: referred to as SSD, basic characteristics: storage and writing are faster than traditional mechanical hard drives. Rely on electronic access to data.
Computer startup process
Step 1: Power on the computer.
Step 2: Start the BIOS (the BIOS may flash at a point during the computer startup process), scan the boot device, and find the operating system from a certain boot device.
Step 3: Read the size of the first sector of the boot device (called the master boot record mbr)
446 Byte bootloader=》grub program
64Byte partition information
2Byte end flag
Step 4: grub program is responsible for the operating system kernel Load into memory and start the operating system.
Step 5: The operating system will let the BIOS to detect the driver.
Network cable installation
There are two types, the first is the more common Gigabit network card-"Twisted pair general 10 Gigabit network card-"Optical fiber, network cable installation color sequence; orange white orange green white blue white green brown white brown