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What's the difference between a process and a process image?
What does one contain that the other doesn't? What are the distinguishing components?
This is all within the context of process control structures and process location in memory.
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A process image is a copy of a given process's state at a given point in time. It is often used to create persistence within an otherwise volatile system. A common example is a database management system (DBMS).
What are the typical elements of a process image? User data: Modifiable part of user space. May include program data, user stack area, and programs that may be modified. User program: The instructions to be executed.
The process image is the storage buffer between the linked IO and the user program. The process image is updated to events. This events are the execution of OBs - the best known is the link to OB1 updating 'normal' inputs and outputs. How the process image is updated, is configured in the PLC hardware.
1. Process Image : Process image is an executable file required during the execution of any process. It consists of several segments related to the execution of the process.
From what I understand, a process image is an image of a process taken when memory is allocated to it before execution. This happens because, when multitasking, the kernel needs to re-enter the process where it left off. If the process were to be changed in mid execution, bad things could happen so the operating system makes a read-only version of the process and uses that during execution.
Here's a webpage with more details on process images
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A process can involve more than its image. It is a live and changing image, hence the name, that is run by the CPU.
A single process can have multiple images at different intervals, along with its effect on the CPU that is not directly included in the image, like arithmetic operations.
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