Operating system with the note
The characteristics of the operating system
1. The concurrency
Concurrency is refers to two or more than two things happen at the same time interval,
Parallel refers to two or more than two things happen at the same time,

2. Shared line
Sharing "refers to all kinds of resources of the computer on which the running program to enjoy together, sharing, there are two ways that mutually exclusive way of sharing and common access method,
Resources sharing based on application of concurrent execution conditions, if the system does not allow concurrent execution procedure, also there is no Shared problems;
Only the operating system provides for the possibility of resource sharing, to make the program truly concurrent execution,

3. The virtual sex
Virtual refers to by some technical means a physical entity into multiple logical counterparts, physical entity is real, and the logical entity is virtual, is a kind of feeling, the user's
Use of multiprogramming technology turns a physical CPU into multiple logical CPU, these logical CPU is also known as a virtual processor,
SPOOLGing technology to a physical input and output devices into multiple logical input/output devices,

Uncertainty
4.Operating system running in an uncertain environment, that is to say, people cannot judge to the behavior of the currently running program,


Operating system interface
Interface is divided into command interface and program interface
Command interface and can be divided into online command interface, offline command interface and interface of the graphical user interface,
Online command interface is to provide online users, it consists of a set of keyboard commands and command interpreter,
Offline command interface for the batch supplied by the user, also known as batch user interface, it is composed of a set of job control need (JCL), batch user cannot directly control my homework, when submitted to the system needs to be in control of the assignment to homework instructions submitted to system together, work is performed, the system will be according to the instructions on the operation manual for operation control and intervention,
GUI interface using the graphical interface, very easy to identify various ICONS each function of the system, various applications and files directly, realistically,

Is also known as the system call, program interface for the user can operate the system at the application level access function, set up by the user program is the only way to obtain operating system services,