10.21 history of operating system development process

History of operating system development

Punched card

A computer room, a user can only use.
The CPU utilization rate

Line processing system

Support for multiple users to use a computer room

Off-line batch processing

High-speed disk

Improve reading speed file

advantage

Improve CPU utilization

Multi-channel technology (where research-based single core)

Multi-channel

Multiplexing (*****) on space

CPU may be provided to a plurality of users

Multiplexing (*****) on time

Save state switching +

advantage

If the CPU met IO operation, CPU use right of the current program will be disconnected immediately (will improve utilization of CPU)

Shortcoming

If a program uses the CPU time is too long, it will immediately use the right CPU program currently executing off (the program will reduce utilization)

Single Channel

When using the CPU is running a series of multiple users
must be allowed to run to completion on a program to run a program

Concurrent and Parallel

Complicated by

Refers looks like running simultaneously, a plurality of programs save state continuously switching +

parallel

It runs on a real sense, in the case of multi-core, simultaneous execution of multiple programs

process

Procedures and processes

Program: a bunch of code that
processes a bunch of code that runs: Process

Process Scheduling

1. FCFS scheduling
   Disadvantages: A program to use, program B must wait for the program to use A use after the CPU
2. Short job priority scheduling
   disadvantages: If the program A uses the longest time, there are N time is short program, must wait for all to use after a short time with the program
3. Round-robin process
   time executed by the CPU 1 second, N program loading, to one second aliquot plurality of N time slices

4. Grading feedback queue
   will be executed into layers priority levels
   Level 1: the highest priority
   level 2: Second Priority
   level 3: analogy
   ......

   When the three states of the scheduler

   Ready state: will enter the ready state when all processes created, ready to dispatch
   blocking state: those who encounter blocking state into the IO operations, IO operation ends, they must re-enter the ready state
   to run state: after the process scheduler, enter the running state

   Synchronous and asynchronous

   It refers to the submission of the task

   Synchronize

   If two tasks required to submit, at the time of submission of the first task, you must wait after the execution of the task, we can continue to submit and execute the second task

   asynchronous

   Means that if two job submission, no place to wait when submitting the first task, and can be submitted immediately perform a second task

   Blocking and non-blocking

   Clog

   Blocking state, met IO will clog

   Non-blocking

   Ready state and run state

   Interview questions: synchronous and asynchronous, blocking and non-blocking is the same thing?

   Not the same concept, synchronous and asynchronous preparation period, blocking and non-blocking is the construction period

   Create a process in two ways

5. Define a task
   windows: create a child process, windows will reload the current parent process code to perform a
   linux / mac: will the current parent process to re-copy the code in to perform

6. A custom class, and inherit Process

   join

   Tells the operating system, so that the child process is finished, at the end of the parent process

   Inter-process data mutual isolation

   The main process and sub-process will have their own name space, isolated from each other so that data

   Property of process objects

   当前进程.pidGet the child process
   os.getpid()to obtain the main process pid number
   cmd view the process ID: tasklist|findstrprocess ID

   Two conditions process ID recovery

7. join.Child process can be recycled to the main process

8. The main process ends normally, the child process will be recycled to the main process

   Zombie process and orphaned

   Zombie process

   Refers to the process has ended, but there are PID number, not destroyed
   Disadvantages: occupation PID number, operating system resources occupancy

   Orphaned

   Refers to the process is still running, but the parent process ends unexpectedly
   operating system optimization mechanisms: a mechanism similar to the orphanage, to help you recover the child has no parent process

   Daemon

   Refers to the end of the primary process, the main process of all child processes created to follow the end, and recovery