I feel that learning a certain kind of knowledge is the biggest driving force is that, when you feel that existing knowledge is not sufficient to solve the current problem when curiosity. To be completely off the bottom of the system. Today began a comprehensive review of the underlying system of knowledge, from the operating system started to UNIX, then the virtual machine. I wish he could get the essence of a thing, with own words.
First, what is the operating system
What computers are? To put it plainly, a collection of hardware plus software. What operating system? It is operating most of the underlying hardware layer of software. With the operating system, we do not need external input such binary information 1010 let the computer deal with, so to speak, is a set of resources computer hardware, operating system, these resources are encapsulated so that you can more easily use it.
For computer resources can be divided into four categories, according to textbooks on the argument, that the processor, memory, I / O devices and information (data and programs), it plainly, refers to the CPU, memory, input-output devices (mouse , keyboards, monitors, etc.), hard drives and software on the hard disk. Operating system encapsulates the computer hardware system, and manages four kinds of computer resources, which is the operating system functions. It is easy to understand.
Second, the operating system development process
Operating system development process is very important, it allows us to realize that technological improvements most important role is to change what is currently the most urgent need for change.
Here in a few words tell us about the development process of the operating system.
(1) manual mode.
The legendary tape operation. The programs and data recorded in the simplest tape, and then into a computer (memory) via tape input (I / O), then the computer is running. At this time we can see that the computer I / O and information (hard disk programs, data) are caused by simple storage and transfer paper. Of course, speed is slow.
(2) off-line input / output.
This can not be off relations with tape, but the tape is pre-loaded into the information on the tape, and then when the computer is running, programs and information from the tape into memory. This of course greatly enhance the speed. We can see, in this way, it means to the computer adds a simple hard drive, programs and data on the hard disk, rather than tape.
(3) a single batch processing system channel.
This is the first operating system. CPU Control "monitoring procedures" will be a job (program and data) on the tape into memory, and then run it, and then call the next job into memory, and then run it. This in turn runs out jobs on the tape. System memory at a time only one program running, CPU only single-threaded processed IO reprocessing program the cycle.
(4) Multi-batch system.
This is a very efficient operating system. Users submit jobs and arranged in a queue on disk, then the scheduler job into a plurality of memory. When a job execution encountered IO requests, not blocking, not the CPU is idle, but to allow the CPU to perform other jobs in memory. This in turn perform each job, keeping occupancy CPU and other system resources as possible.
(5) time-sharing system.
This is a multi-user system, the main features is more simultaneous users, each user has their own computer terminal to operate. Time-sharing system with a very classic slice of time that each user, each job in a time slice, are in turn run, and run only a very short period of time, it looks as if each user has monopolized the entire computer same. Time-sharing system is mainly used to query the system.
(6) real-time systems.
Real-time system may be seen as a requirement for a more accurate higher internal time-sharing system. However, this "time" is not necessarily controlled by time slice, it may be controlled by a set deadline. Internal system is more real-time acquisition and control tasks. To put it plainly, it is a precise multi-tasking system.
(7) the computer operating system.
This matter is very simple, there are single-user single task operating system (CP / M, MS-DOS, etc.), single-user multi-tasking operating system (Windows95, XP, etc.), multi-user multi-tasking operating system (UNIX OS, etc.).
Third, the operating system structure
(1) unstructured OS (first generation)
This is the earliest operating system, only the pursuit of function and achieve without the bottom.
(2) OS modular structure (second-generation)
The OS is divided into a number of separate modules, such as process management module, a memory management module, document management modules, and each module is divided into respective sub-module, so constantly broken down, there is a clearer system of modular construction. However, because of the modular design, the design of each module go hand in hand, there is no reliable "determine the order", this design is also known as "disorder modular approach." This generation OS on the basis of the first generation plus the division of the module, then a big step forward.
(3) OS hierarchical structure (third generation)
From the bottom-up hierarchical design, the bottom only for hardware, single function and correct, then look at each of the lower layer is transparent, function continuously enriched, to continue high-level abstraction level depends only on its bottom. This is also reflected in the object-oriented thinking. This structure and our well-known network protocol architecture is very similar. This structure in the software design is very common. It simply is divided in layers, abstract continue, only the operation in each layer.
(4) OS microkernel architecture (structure modern OS)
Microkernel OS configuration of the system is divided into two parts: a plurality of micro-kernel systems and servers. Microkernel means is small enough, to achieve the most basic part of modern OS features. It is responsible for the communication server hardware basic contact with the outer layer of the two basic functions of the system. The outer layer of system refers to the internal server operating system, various system services are abstracted into a modular server architecture, it is represented by a process, such as file servers, process servers. We all know that the essence of the message is the server request and response, which is very suitable for today's distributed processing system requires. Be carried out with a simple and efficient enough microkernel actual processing of individual servers, each server is in general are modular, and the server itself is built on different levels of the OS, this design pattern is not only reliable, and scalability and performance are very superior. This design is really elegant.
Reproduced in: https: //www.cnblogs.com/zrtqsk/p/4064155.html