An operating system refers to a collection of programs that controls and manages the hardware and software resources of the entire computer system, rationally organizes and schedules the computer's work and resource allocation, and then provides convenient interfaces and environments for users and other software. The operating system is the most basic system software in the computer system. The operating system is the core of the software.

concurrent

shared

virtual

asynchronous

computer system resource manager

The interface between the user and the computer hardware system

Realized the expansion of computer resources

The user monopolizes the entire machine, resulting in low resource utilization and insufficient CPU utilization;

In order to solve the contradiction between man and machine and the mismatch in the speed of CPU and IO equipment; Features: automatic (a batch of jobs can be run automatically one by one without human intervention under normal circumstances), sequential execution, single-channel (program completion or occurrence Switch to the successor program only when an exception occurs); Disadvantage: Only one job is stored in the memory at a time. When an IO request occurs, you need to wait for low-speed IO.

In order to further improve resource utilization and system throughput, multiprogramming technology was introduced; Features: multi-channel, macro-parallel, micro-serial; Advantages: high resource utilization, large system throughput; Disadvantages: long user response time, no human-computer interaction function (users do not know the running status of their own programs and cannot control the computer) ); Problems need to be solved: how to allocate processors, memory allocation issues for multi-programs, how to allocate IO, how to organize and store large amounts of programs and data while ensuring security and consistency;

Using time slice method, human-computer interaction is possible; Simultaneity: Multiple users use the same computer; Interactivity: Users directly control the program running through the terminal through human-computer dialogue; Independence: Multiple users in the system can operate independently of each other Carry out operations without interfering with each other; timeliness: user requests can be responded to in a short time;

In some applications, the system needs to be able to process external information within a specified time (shorter than the time slice) (such as aircraft booking systems or missile guidance systems). Therefore, real-time operating systems emerge as the times require. Features: timely and reliable; Category: hard/soft real-time system

Sharing of various resources in the network and communication between computers

The essential difference between a distributed OS and a network OS is that several computers in a distributed operating system collaborate with each other to complete the same task. Features: Distribution, parallelism

Classification

User mode->Core mode

clock management

Interrupt mechanism

primitive

Data structure and processing in the system

Device management

File management

process control

process communication

Memory management