The goal of the operating system
The objectives of the operating system are related to the application environment.
For example, the OS used in the query system is expected to provide good man-machine interaction;
For OS applied in industrial control, weapon control and multimedia environment, it is required to have real-time performance.
For the OS configured on the microcomputer, the more important is its ease of use.
The objectives of configuring an operating system on a computer:
convenience, availability, scalability, and openness.
1. The convenience
Users use compilation commands to translate programs written in high-level languages into machine code，
or to manipulate the operating system directly through the various commands provided by the OS.
2. Effectiveness
Improve system resource utilization: processors and I/O equipment are often left vacant
Improve system throughput: speed up the program, improve the throughput of the system
3. Extensibility
The microkernel structure can conveniently add new functions and modules,
and modify the original functions and modules, with good scalability.
4. Open
Comply with OSI international standards
Operating system development process
1.A computer system with no operating system configured
Manual operation mode：The programmer loads the punched tape (or card) into the tape input machine (or card input machine)
Offline input/output (off-line I/O)：Data (programs) from paper tape (CARDS) are fed into magnetic tape and transferred into memory at high speed from the tape.
2.Single channel batch system
The supervisor first loads the first job on the strip into memory and gives the job control of the run. When the job is processed, control is returned to the control program.
3.Multi-channel batch system
The jobs submitted by the user are stored on the external storage and formed into a queue.
4.Time-sharing system
Human-machine interaction
Shared hosting
5.Real-time systems
Aircraft autopilot system, train reservation system, multimedia system, embedded system
Development of microcomputer operating system
1.Single-user single-task operating system
2.Single-user multitasking operating system: Windows
3.Multi-user multi-task operating system: UNIX
Basic operating system features:
concurrency, sharing, virtual, asynchronous
1.Parallelism and concurrency:
for example, in 1 second, 0~15ms program A runs; 15~30ms program B runs; 30~45ms program C runs; 45~60ms program D runs, so it can be said that, in the 1 second interval, macroscopically there are four programs running at the same time, but microcosmically, program A, B, C, D are time - sharing alternate execution.
Process:
A system in which one process is created for the same application's calculator and one for the I/O program.
In memory, a process is created for multiple programs to be concurrent
Processes and concurrency the most important basic concepts in modern operating systems.
2.Sharing: or resource reuse
Mutually exclusive sharing: resources such as printers, tape drives, and so on that allow only one process for a period of time are called critical resources (or exclusive resources).
Simultaneous access: a disk device that allows several users to access the file simultaneously.
Concurrency and sharing are two of the most fundamental characteristics of a multi-user (multi-task) OS.
3.virtual
Time-division multiplexing (TDM) : using idle time to improve utilization
Virtual processor technology, virtual equipment technology
Air division multiplexing: using free space to improve utilization
In the early 20th century, frequency division multiplexing (FDM) was used to improve the utilization of channels.
4.asynchronous
The emphasis of the program is different, some need less computation, some more I/O, so that may enter the memory of the job to complete, which is asynchronous process.
OS architecture: hundreds of people work together to design the operating system, resulting in "software engineering"
1.Traditional operating system architecture
Unstructured operating system
Modularize the operating system
Hierarchical structure OS：From disorder to one-way order
2.Client/Server Model
3.Object- oriented Programming
Object: if the file is an object, the transaction is called an instance of the object.
Variables: variables are file type, file size, file creator, and so on.
Method: contains actions to the file, such as creating the file, opening the file, reading the file, writing the file, closing the file, and so on.
Variables (data) are hidden from the outside world and must be accessed by methods (action functions).
Object class: a group of roughly similar objects.
A class is an abstraction of an object, and an object is an instance of the class.
Inheritance: defines a new class based on an existing class
Multiple inheritance: a subclass obtains inheritance from more than one parent class
Subclasses inherit the variables and methods of the parent class
4.Microkernel OS structure
2020-05-01