Operating Systerm: How a READ operation takes place?

Please elaborate your question.
Do you means the READ/WRITE operation with respect to the programming concept or something else.
please make it clear.

Try to be close to your question.

You can read memory. And this can be different depending if you are reading ram or rom.

You can read something from the disk drive.

And you can read a device like a serial port or a keyboard.

And how all of the above is done can be quite different depending on if you are using assembly language and directly accessing the device... Or if you are using a higher level language and using an operating system to access the device.

In the hardware case, you would need to be reading data sheets on the hardware to learn how something can be read.

In the operating system case, you would need to be reading the operating system programming manual to learn how something can be read.

The two can be quite different!