How is copy paste possible?

Question

I was wondering after using computer for a long times it feels like copy paste was fundamental feature but I know it is not. So the question is how does this really work?

Answer 1

The first thing you need to realize is that "copy and paste" as well as "drag and drop" are a form of IPC (Inter-process communication) since the data is being transferred from one application to another. This mechanism is usually provided by the same subsystem or service which is responsible for managing the graphical user interface.

This subsystem provides a mechanism for "source" and "destination" applications to negotiate about the format of the data that should be transferred and if they "agree" on some common format then the data can be transferred.

An example to illustrate the concept:

1. User selects the text in the web-browser and presses Ctrl+C.
2. Browser tells the windowing system that it has some data available for copying. Note that no data is copied at this step.
3. User opens a text editor and presses Ctrl+V.
4. Text editor tells the windowing system to provide it the contents on the clipboard in plain-text format.
5. Windowing system tells the browser to provide its shared data in plain-text format.
6. Browser converts its data from HTML (or something else) to plain-text and transfers it to the text editor via windowing system. Note that this conversion is not always possible (depending on the formats and applications), hence you sometimes can't paste the copied data.

Technical details

• On Windows this functionality is provided via Clipboard API as Ken White mentioned.
• On Linux (and probably everywhere else) the clipboard functionality is not strictly speaking a part of the OS and is provided by the Window Server/Manager (which is really just a service process) via a windowing system protocol such as X protocol or Wayland.