Where is a PNG file first created and how fast?

Dear all

I want to find out, how fast my system is creating a PNG file.

1.

In what part of the hardware, is the iDAT chunk first created, CPU, memory?

2.

In what part of the hardware, is the WHOLE PNG file first created, CPU, memory?

I have conducted a test, screenshot: https://imgbb.com/547f4XT

At which of the points 1-8 on the screenshots is:

3.

The iDAT chunk first created?

4.

the WHOLE PNG file first created?

Thank you for replying

Best regards