Relationship between Oracle instance _ of oracle.exe Oracle Database Engine

For Program For members, they only need to pay attention to the three most important engines in the Oracle database engine,
SQL Script Engine, PL/SQL script engine, and JVM
(According to my current understanding, the engine is a concept corresponding to the scripting language, but here, we may consider JVM as an engine for the time being)

These three engines are used to parse and execute programs (separate SQL programs, PL/SQL programs, Java programs, or their mixture) that are sent by user processes to the Oracle server !)
These three engines are not independent of each other, but can cooperate with each other, as needed!

The Database Engine accesses and operates the Oracle instance connected to the user, and finally completely parses the request of the user process to generate a result.
The result is then fed back to the user through the Oracle Net component.

The user receives the correct result! The user is very happy! The results are perfect!

[Problem] I am not happy with the question of when and where!
Question 1: When will the Oracle database engine be loaded into the memory? Can I control it by myself? I don't want it to be loaded into the memory without knowing it clearly...
Question 2: Where is the Oracle database engine? The Oracle engine must be in the memory, and there must be one process or multiple threads. So where is it ???

With regard to this question, I can only draw the following conclusions through the materials I have currently consulted (only my own understanding, which is still to be verified. At present, the materials are not enough. So is for reference only! ^_^ ):
It is certain that after oracleservice *** is started in the Windows Service Manager, you can find another process oracle.exe by viewing the task manager. There is only one more process !!! Generally, this operation is only intended to start an oracle instance (also known as an oracle routine) on the server! Only! Only! Only! Only!
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Just !?? Now, where is the Oracle database engine ???
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I really want to know the answer to this question. But now I can only test it in oracle.exe, And it will exist in the oracle.exe process as a child thread !!
My current conclusion is: oracle.exe consists of two important parts: Oracle instance _ and _ Oracle database engine.

I wonder if this idea is correct. I am very grateful to you for your guidance!
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