Linux Study Notes (1) -- Understanding Linux and hosts

1. CPU
A. the CPU has the so-called "Frequency Doubling" and "external frequency". The external frequency is the speed at which all the system interface devices operate. The frequency doubling is the computing speed added during the CPU operation! The multiplication of the two is the CPU frequency. However, because the interface device is not so fast, some interface devices need to divide the external frequency into a number before communication. For example, the normal speed of the PCI interface is 33 MHz. Therefore, if the external frequency of your CPU is 133, the speed of the interface device must be divided by 4 to communicate with the system! Generally, the higher the frequency, the faster the CPU computing speed. Taking Intel's piII frequency 933mhz as an example,

CPU external frequency and frequency doubling: 133 (external frequency) x 7 (Frequency Doubling) MHz
Ram frequency: usually the same as the external frequency of the CPU, 133 MHz
PCI interface (including network card and sound card interfaces) 133/4 = 33 MHz
AGP interface: 133/2 = 66 MHz (this is the normal AGP frequency !)

B. another thing to note is that "CPU is classified", which is the i386, i586, and i686 we often see. This is the optimization of CPU of different levels by many programs.

2. graphics card (VGA Card)
GPU: To avoid CPU troubles caused by a large number of 3D images, the display card developer inserts a hardware on the display card that can process these very CPU computing time to process the image data, as a result, not only does the image processing speed increase, but the CPU resources are also added to execute other work.
Memory is also available on the vgacard. This memory size can affect the screen output resolution and image quality.

3. PCI adapter
Taking a hard disk as an example, this SCSI interface is used in addition to the mainstream IDE/SATA interfaces of personal computers. Because the SCSI interface is relatively stable, and the device runs fast, it consumes less CPU resources. Currently, the SCSI adapter is the hard disk transmission interface of a general large server host. However, it is enough to use the IDE/SATA interface for personal computers.

4. device code of hardware and hardware in Linux
Code of the device in Linux
IDE Hard Drive/dev/HD [a-d]
SCSI hard drive/dev/SD [A-p]
CDROM/dev/CDROM
Floppy disk/dev/FD [0-1]
Printer/dev/LP [0-2]
Mouse/dev/mouse
Tape drive/dev/ht0 (IDE) or/dev/st0 (SCSI interface)
Network Card/dev/ethn (N starts from 0)

5. Hard Disk connection and hard disk number
Generally, there are two cabling interfaces on the motherboard produced after 586 (the cabling is used to connect the hard disk to the motherboard). We call this interface an IDE interface, this is also the mainstream hard disk interface (which has been replaced by SATA ). To separate the order of Hard Disk reading, the two interfaces on the motherboard are called the primary (main) and secondary (secondary) ide interfaces respectively, or ide1 (primary) and ide2 (secondary ).
There are two jacks on each line, that is, a line can be connected to two ide interfaces (hard disk or optical drive), and you have two lines, so a motherboard is in the default situation, each device can be connected with four ide interfaces, and the master and slave disks on each cable are differentiated Based On jumpers.
IDE \ jumper master slave
Ide1 (primary)/dev/had/dev/HDB
Ide2 (secondary)/dev/HDC/dev/HDD
If there is only one hard disk, and the hard disk is connected to the ide2 master, the code in Linux is/dev/HDC.

6. Hard Disk partitioning
Generally, a hard disk is composed of the smallest physical unit (sector). When multiple sectors form a concentric circle, it is called a cylinder, and finally the size of the entire hard disk.
The hard disk is divided into two areas: the Master Boot recorder to prevent the information area of the hard disk, and the other is the place where the actual file data is stored. MBR records the boot program and the disk partition table (partition table, the N disk blocks are from the X to the Y ), our partition operation is to modify the partition table in the MBR. You can only have one extended partition. The sector at the beginning of each partition has a special block called a super block.

One hard disk partition:

7. XWindow
Press [CTRL] + [alt] + [backspace] in the image of X to restart X and read the setting file directly.
[CTRL] + [alt] + [F1] ~ [F6], use the command line to log on to tty1 ~ Tty6 terminal; [CTRL] + [alt] + [F7]; GUI desktop.
Startx can start the graphic interface from the command line.

8. Linux Manual
Meanings of different numbers in manual:

Code	Content
1	Commands or executable files that can be operated by users
2	System Core callable functions and tools
3	Some common functions and libraries)
4	Device File description
5	Set the format of a file or some files
6	Games)
7	Conventions and protocols, such as Linux standard file system, network protocol, ASCII Code, etc.
8	Available management commands of the system administrator
9	Kernel-Related Files

Whatis = man-F for more information
Apropos = man-K, search keyword