Four basic characteristics: 1. Concurrency refers to the occurrence of two or more events within the same time interval. 2. Sharing, that is, resource sharing, refers to the resources in the system being used by multiple programs in memory. 3. Virtuality refers to turning a physical entity into several logical counterparts through a certain technology. 4. Asynchrony. In a multiprogramming environment, multiple programs are allowed to execute concurrently. However, due to limited resources, the execution of the process is not consistent to the end, but stops and goes, advancing at an unpredictable speed, that is, the process The execution order and execution time are uncertain.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
The operating system (English: Operating System, abbreviation: OS) is a set of interrelated system software programs that supervises and controls computer operations, uses and runs hardware and software resources, and provides public services to organize user interaction. According to the operating environment, operating systems can be divided into desktop operating systems, mobile operating systems, server operating systems, embedded operating systems, etc.
The four basic characteristics of the operating system
The four basic characteristics of the operating system are: concurrency, sharing, virtuality, Asynchronousness
1. Concurrency: refers to two or more events occurring within the same time interval, that is, the device will execute this event and then execute that file, etc. events share the same device.
The concurrency of the operating system refers to the existence of multiple running programs in the computer system at the same time, so it should have the ability to process and schedule the execution of multiple programs at the same time. In this multi-programming environment, within a period of time, there are multiple programs running at the same time from a macro perspective, but at each moment, only one program can actually be executed in a single-processor environment, so from a micro perspective, these programs are still running separately. Executed alternately from time to time. Operating system concurrency is achieved through time sharing. Parallelism means that two or more events occur at the same time, that is, two or more events do not affect each other, and the computer completes two or more tasks at the same time.
2. Sharing: Resource sharing refers to the resources in the system being used by multiple programs in memory.
There are two ways to share: mutually exclusive sharing and simultaneous access.
Mutually exclusive sharing mode: Although some resources in the system can be provided to multiple processes, only one process is allowed to access them within a time period
Simultaneous sharing mode: Certain resources in the system allow multiple processes to access the resources "simultaneously" within a period of time
This is from a macro perspective. Microscopically, multiple processes still access the resource alternately.
For example:
Mutually exclusive sharing: Both QQ and WeChat support video chat, but QQ and WeChat cannot be opened for video chat at the same time.
Simultaneous sharing: We can transfer file A and file B at the same time. From a macro perspective, files AB are transferred at the same time, but from a micro perspective, the two transfer processes access the disk alternately.
Note: Concurrency and sharing are the most basic features of multi-user OS; resource sharing is conditioned on the concurrent execution of processes; effective management of resource sharing by the system requires coordinating access by processes
The relationship between concurrency and sharing
For example, in the above example of transferring files, QQ sends file A and WeChat sends file B:
Two processes are executing concurrently (concurrency)
Need to share access to hard disk resources (shareability)
If concurrency is lost If there is only one process running in the system, then sharing is meaningless.
If sharing is lost, QQ and WeChat cannot access hard disk resources at the same time, and cannot send files at the same time, that is, they cannot be concurrent.
This is why concurrency and sharing are conditions for each other.
3. Virtuality: refers to turning a physical entity into several logical counterparts through a certain technology.
Virtuality is a management technology that turns one physical entity into multiple logical counterparts, or turns multiple physical entities into one logical counterpart. The purpose of using virtual technology is to provide users with an easy-to-use, convenient and efficient operating environment.
For example, the time-sharing system virtualizes one machine into multiple machines, which will make user resource sharing more convenient in the future. Specifically, there are two types of virtualization:
1) Virtual memory: The memory occupied by the current job to be processed is smaller than the computer's memory. Part of the job is transferred first, and when this part of the job is processed After that, the next part of the job to be processed is transferred, so the program thinks that the computer memory is large enough, so it virtualizes a larger memory
2) Virtual peripherals: When the computer is connected to multiple When using multiple external devices, the time difference between multiple peripherals working is within an acceptable range and they are approximately working at the same time. This is a virtual peripheral.
4. Asynchronousness: refers to the "stop-and-go" of multiple programs executed concurrently in the system, that is, they may face interruptions at any time and respond to requests at an unpredictable speed. Push forward.
In a multiprogramming environment, multiple programs are allowed to execute concurrently, but due to limited resources, the execution of the process is not consistent to the end; instead, it stops and goes, advancing at an unpredictable speed, that is, The execution order and execution time of processes are uncertain. This is the asynchronous nature of the process.
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