Brief analysis on the principle of computer (II.)

1. System calls: System call, the kernel is used by the operating system to make the upper-level program use the underlying hardware.

2. Library (API): Between the kernel and the upper layer of the program, is a lot of direct calls to the underlying hardware software call interface collection, so the operating system in addition to provide kernel and system calls, but also need to output, this output is a higher-level interface output, this interface is called the library. The library itself is an application, but this kind of program does not have the execution entrance of the program, cannot run independently, can only be executed when other program calls. The execution environment in which the library exists is called. Call libraries are called Library calls, which are different from the kernel's system calls.

3. Any time the application is unable to access the kernel in the 0 zone

4. The memory is actually divided into 3 segments: the first paragraph is to give the BIOS power-on self-test; the second segment is mapped by the kernel 0, allowing the kernel to start normally; The third paragraph reads the general data.

5. Memory fragmentation is ubiquitous, the operating system can flexibly adjust memory to avoid fragmentation, indicating that the operating system is a very complex system

6.Shell is called the kernel, is a software that can accept and understand user instructions, and transfer information to the kernel, the kernel commands an application to launch an interface (interface), from a broad sense of two kinds: graphical user interface; command line interface.

7. Functions of the kernel:

Process Management

Memory management

File system

Network functions

Hardware Drivers

Security mechanisms

8. The original Linux was just a kernel, requiring gun's accompanying software, such as the glibc and GCC of the gun. Then by the Redhat, SLS, Debian, SuSE and other publishers packaging distribution to add their own understanding of the system and their respective logo. Manage the software of gun, Redhat Software Management tool RPM. In any case, as long as the binaries based on the Linux kernel are compiled, you must follow the GPL, which is to share all the source code.

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Brief analysis on the principle of computer (II.)