define

  • Responsible for the management and coordination of hardware, software and other computer resources

  • Provide easy-to-use services for upper-layer users and applications

  • It’s a system software

Functions and objectives

Resource manager

  • Processor management

  • Memory management

  • File management

  • Equipment management

Provide services to users

The command interface

  • Online command interface users say a word, the system does a word

  • Offline command interface the user says a lot and the system does a lot

Program interface

  • Consists of a set of system calls

    System call = System call

  • Such as win system call C disk DLL file, in order to achieve the function

GUI The user graphical interface

  • Action such as dragging and dropping files according to graphics

  • Expansion of hardware machines

Supplementary knowledge: process is the execution process of a program. Before execution, the program needs to be loaded into memory to be processed by the CPU.

Characteristics of the

concurrency

  • Concurrency is defined as the occurrence of two or more events at the same time interval, which are macroscopically simultaneous but microscopically alternating

  • Distinguish parallelism: When two or more events occur simultaneously at the same time

  • Operating system concurrency refers to the existence of multiple running programs in a computer system. Example: a four-core processor

Shared

define

  • Resource sharing. Resources in a system that can be used by multiple concurrently executing processes in memory

way

The mutex Shared

  • Some resources in the system can be used by multiple processes, but only one process is allowed to access the resources in a period of time

  • For example: QQ and wechat open a video at the same time, only one program can call the camera

At the same time to share

  • A resource in a system that can be accessed simultaneously by multiple processes over a period of time

  • For example: QQ access file A, wechat access file B, can access the hard disk resources at the same time, micro for alternate access to hard disk

Relationship between concurrency and sharing

  • Two processes are executing concurrently (concurrency)

  • Requires shared access to hard disk resources (shareability)

  • If concurrency is lost, only one program is running on the system, and sharing loses its meaning

  • If the loss of sharing, QQ and wechat can not access hard disk resources at the same time, it can not be realized at the same time to send files, there is no concurrency

  • Conclusion: Concurrency and sharing are mutually existing conditions

virtual

define

The transformation of a physical entity into a number of logical counterparts, physical entities that actually exist, and logical counterparts that are perceived by the user

For example,

On a single core processor, why can you run multiple applications at the same time when you have multiple applications open

classification

Time division multiplexing

For example, the virtual processor microcosmic physical machine in each minute time for each process services

Air division reuse technology

Such as virtual memory technology

asynchronous

define

In a multiprogram environment, multiple programs are allowed to execute concurrently, but due to limited resources, process execution is not consistent. For example, when a program is processed, it can return the request result synchronously and then process the program asynchronously

Several relationships with each other

  • Without concurrency and sharing, there is no virtuality or asynchrony, so concurrency and sharing are the two most basic characteristics of an operating system