1. The concept of operating system
1. Definition
The operating system is a large-scale program system, which is responsible for the allocation and scheduling of all the software and hardware resources of the computer, controls and coordinates the activities of multiple tasks, and realizes the access and protection of information. It provides a user interface to enable users to obtain a good working environment.
The core software of the computer system of the operating system can be divided into operating systems according to different functional characteristicsMulti-pass batch processing system，Personal Computer System，Network operating system，Distributed operating system
(The purpose of the system call is to request system services)
- Multi-pass batch processing system: improve the throughput and efficiency of the system (disadvantages: loss of interactivity)
- Real-time operating system: real-time scheduling of system resources (the goal is to respond quickly)
- Network operating system:
- Distributed operating system:
- Time-sharing operating system: features (timeliness, exclusivity, interactivity)
UnixTime-sharing operating system:
In a time-sharing operating system, the time slice is fixed, and the more users, the longer the response time.
FROMThere is no feature of multi-pass batch processing
2. Goals
Convenience: The computer system is easier to use after configuring the OS
Effectiveness: improve resource utilization; increase system throughput
Scalability: OSde structure (such as hierarchical structure: unstructured development -> modular rapid structure -> hierarchical structure -> microkernel structure)
Openness: OS follows the scope of world standards.
3. Function
- OS as between the user and the computer system hardware interfaces (API / CUI / GUI)
- OS is the manager of computer system resources (processor, memory, I/O devices, files)
- The OS realizes the abstraction of computer resources (OS is an expansion machine/virtual machine)
4. Features of the operating system:
concurrent execution of programs, resource sharing, independence, and asynchrony.
5. Development
With the development of VLSL, computer hardware has developed rapidly, and higher requirements are placed on the operating system, and the operating system is responsible Manage the resources of a computer system including processors, memory, equipment and files
Processor management is used to allocate and control processors
Memory management is responsible for the allocation and recovery of memory
I/O device management is responsible for the allocation (recycling) and manipulation of I/O devices
File management is used to realize file access, sharing and protection
6. The basic characteristics of modern operating systems: concurrent execution of programs, resource sharing, and asynchronous operation
7. Life examples of operating systems.
Computer booking systems should install network operating systems.
Computer language system learning should install time-sharing operating systems.
8. The hardware support necessary for the implementation of the operating system is: address translation mechanism, interrupt transposition storage protection mechanism
9. Time-sharing system needs to use multi-program design technology interrupt processing terminal command interpreter system call
10. Support CPU and peripherals Parallel working hardware supports channels, interrupts, and buffers.
11. Privileged instructions are turned off and interrupts are changed to a managed state restart.
12. The core file system of the operating system. Device management. Memory management. CPU management.
13. The goal of operating system design:
scalability , Openness, Convenience, Effectiveness
14. The user can call the system by command mode. Graphical window
interface : User interface, program interface Offline user interface Graphical user interface (GUI)
15. The operating system is a group of control and management computers Hardware and software resources Reasonably schedule various jobs and a collection of programs that are convenient for users.
16. Two ways of resource sharing are mutually exclusive and shared. Simultaneous access.
17. Only one process is allowed to access resources within a period of time. Called critical resource
18. Two ways to realize virtual technology are used in the operating system, time division multiplexing and space division multiplexing
2. The development process of the operating system
1. Computer system without operating system (manual operation stage in the 1940s)
- Manual operation mode: The user monopolizes the whole machine, and resources are idle and waste.
Manual loading and unloading, manual judgment, manual modification and debugging of memory commands cause the CPU to be idle; completion in advance causes the CPU to be completely idle in the remaining reserved time;
CPU idle waiting time caused by the slow speed of the I/O device and the CPU speed - Offline input and output (Off-Line I/O) mode. Reduce the idle time
of the CPU and improve the I/O speed
2. Single-channel batch processing system (50s)
- Solve the problem:
The single-pass batch processing system is formed in the process of solving the contradiction between man and machine and the speed mismatch between CPU and I/O equipment. The batch processing system aims to improve the utilization of system resources and the throughput of the system. (But the single-channel batch processing system still cannot make full use of resources, so it is rarely used now.)
Single-channel batch processing is divided into: online batch processing, offline batch processing.
Online batch processing: CPU directly controls job input and output
offline batch processing: Control job input and output by peripheral machine
- Disadvantages:
The system resource utilization is low (because there is only one program in the memory, the CPU is idle until the I/O request is successful)
- feature
- Automaticity. Under normal circumstances, a batch of jobs can run automatically in sequence without manual pre-processing.
- Sequential. Each job is sequentially entered into the memory,
- FCFS single pass. There can only be one job in the memory at any time.
3. Multi-channel batch processing system (early 1960s)
purpose: To further improve resource utilization and system throughput
In this system, all jobs submitted by users are stored in the external memory first. When job A is executing an I/O request, the CPU is idle. At this time, job B is called to prevent the CPU from being idle. Similarly, call the job according to a certain algorithm to prevent the CPU from being idle: Note
advantage：
High resource utilization
High system throughput
Disadvantage:
Long average turnaround time (The turnaround time of a job refers to the time from when the job enters the system until it completes and exits the system.) No interactive ability
to sum up:
- Multi-channel: There are multiple jobs in the memory at the same time
- Macroscopically parallel: There are multiple programs running in the memory at the same time. In a certain period of time, each program advances to varying degrees.
- Microscopically serial: at most one job occupies the CPU at any time, and multiple programs alternately use the CPU
4. Problems to be solved:
| Processor management issues | Memory management issues (memory allocation and protection) |
|---|---|
| I/O device management issues | Document management issues (organization and management of documents) |
| Job management issues | The interface between the user and the system (the OS should also provide an interface between the user and the OS to facilitate user operations) |
5. Time-sharing system (mid 1960s)
Time-sharing system refers to the connection of multiple terminals with monitors and keyboards to a host, and at the same time allows multiple users to use their own keyboards to use the computer in an interactive manner and share resources in the host.
The key issue:
| Timely reception (multi-channel card and buffer) | The job goes directly to the memory and does not allow a job to occupy the processor for a long time |
|---|---|
| Real-time processing (divided time slices) | Multiple users use the host in time-sharing, and each user is allocated a time slice. After this time slice is used up, the operating system allocates the processor to another user. In this cycle, each user can periodically obtain the right to use the CPU. Every user has a feeling of exclusive CPU. |
feature:
| Multiplex | Allow the same host to connect to multiple terminals |
|---|---|
| Independence | Each user owns a terminal; each user cannot feel the existence of other users. |
| Timeliness | Timely response to user requests |
| Interactivity | Can conduct a wide range of man-machine conversations |
6. Real-time operating system (mid 1960s)
-
Concept: The system can respond to external event requests in a timely manner, complete the processing of the event within the specified time, and control all real-time tasks to run in a coordinated manner.
-
feature:
Multiplex
- For real-time processing systems, the system serves multiple terminals according to the time-sharing principle;
- For real-time control systems, the system often collects multiple on-site information; and controls multiple objects or multiple actuators.
Independence
- Real-time processing system, each terminal user makes a service request to the real-time system independently of each other;
- Real-time control system, the collection of information and the control of objects do not interfere with each other.
Timeliness (start deadline/finish deadline)
Interactivity (limited to access to dedicated service programs)
Reliability (multi-level fault tolerance measures to ensure system and data security)
7. Microcomputer operating system
Single-user single-task operating system: CP/M (75 years), MS-DOS (81 years).
Single-user multitasking operating system: OS/2 (87 years), MS WINDOWS (90 years windows 3.0).
Multi-user multi-tasking operating system: UNIX (70 years)
8. Multi-processor operating system
9. Network operating system
Three, the basic characteristics of the operating system
1. Concurrency
- It means that two or more events occur within the same time interval.
- In a period of time, each job can move forward to varying degrees. But at any one point in time, only one channel can occupy the CPU.
- Serial: Only one job can be placed in the memory at a time, and other jobs can be executed in the memory only after it is completely executed.
- Parallel: In an environment with multiple CPUs, multiple jobs are placed in the memory. At any point in time, multiple jobs may be executed simultaneously on different CPUs.
2. Sharing
The resources (hardware resources and information resources) in the system can be used by multiple concurrently executing programs instead of being monopolized by one of them. There are two ways of resource sharing: mutually exclusive sharing (critical/exclusive resource) access and simultaneous access.
3. Virtual
Virtuality is a management technology that turns a physical entity into multiple logical counterparts, or turns multiple physical entities into a logical counterpart. The purpose of using virtual technology is to provide users with an easy-to-use, convenient and efficient operating environment.
| CPU | Multi-programming technology / "virtual processing machine" for each user (process) |
|---|---|
| Memory | Address space occupied by each process (instruction + data + stack) |
| I/O device | Printer, multi-window or virtual terminal |
4. Asynchronous
In a multi-program environment, multiple programs are allowed to execute concurrently, but due to limited resources, the execution of the process is not consistent. But stop and go to the unpredictable pace to move forward, this is the asynchronous nature of the process.
Fourth, the main functions of the operating system
1. Processor management functions: process control, process synchronization, process communication, scheduling (job scheduling, process scheduling)
2. Memory management functions: memory allocation, memory protection, storage expansion, address mapping
3. Equipment management functions: buffer management, equipment allocation, equipment handling
4. File management function: file storage space management, directory management, file read/write management and protection
5. The interface between the operating system and the user: command interface, program interface, graphical interface
6. New features of modern OS:
System security: In order to ensure the confidentiality, integrity and availability of data, commonly used technologies: authentication technology, password technology, access control technology, anti-virus technology
Network functions and services: network communication, resource management, application interoperability,
support for multimedia
Five, the structural design of the operating system
Traditional operating system structure
Unstructured OS
Modular OS structure
Layered OS structure
Modern OS structure-microkernel structure