OCR Reading Notes-Chapter 3 Process

Chapter 3 process description and Control

1. What is a process?

A program being executed

Program instance being executed on Computer

Entity that can be allocated to the processor and executed by the processor

An activity unit with the following features: execution of a set of command sequences, a set of current states and related system resources

Processes can be characterized as the following elements:

Identifier: each process has a unique identifier.

Status:

Priority:

Program counter: the sequence of commands to be executed in the program

Memory pointer: pointer to program code and process-related data, and share the memory block pointer with other processes.

Context Data: Data in the Processor register during execution

I/O status information:

Audit information

The preceding information is placed in the -- Process Control Block.

The Process status is switched by the dispatcher.

Cause of Process Creation

1. The new batch processing job operating system accepts new jobs and reads the next job control command

2. Interactive login terminal users log on to the system

3. The operating system provides a service. The operating system creates a process to execute a function on behalf of the user program.

3. Existing process-derived User Program Creation

Process Termination

1 halt execution completed

2. Exit the terminal interactively.

3 errors or faults

5. State model and transition

Ready, run, exit, block, new

Process description

The operating system maintains four different types of tables.

Memory, I/O, files and processes

Memory table-same as primary storage and secondary storage

Process Control Structure

To manage and control processes in the operating system, you must know the process location and process attributes.

What is the physical representation of a process?

A process must include at least one or more programs executed, as well as local variables, global variables, and any defined data units associated with these programs. Therefore, you need to store the program and data of the process in the memory.

Stack of parameter passing during program execution tracing process invocation and process.

The set of attributes becomes the process control block.

The collection of programs, Data, stacks, and attributes becomes a process image.

Process images can be partially stored in primary and secondary storage. To execute the process, the entire process image must be loaded into the primary storage or load

Virtual storage. Therefore, the operating system needs to know the location of the process on the disk.

Typical process image elements

User Data

User Program

System Stack

Process Control Block

Process control blocks include

Process ID

Process status information

Process control information

Process Control

User Mode

Privileged Mode

There are two modes: Protecting the operating system and important operating system data tables from interference by user programs

One digit in the program status word represents

Process Creation

1. assign a unique ID

2. Allocate space

3. initialize the process control block

4. Set the correct connection .. Scheduling queue

5. create or expand other data structures

Process Switching

When to switch Processes

1. Interrupt --- external event reflection

2 traps --------------------- handle error exceptions

3. System Call --- Call system functions

Differences between interruptions and traps

Interrupt --- some type of external events irrelevant to the currently running process

Trap-errors or exception conditions generated by the currently running process

Common interruptions

Clock interruption

I/O interruption

Page missing for memory failure