README

What happens when...
====================

This repository is an attempt to answer the age-old interview question "What
happens when you type google.com into your browser's address box and press
enter?"

Except instead of the usual story, we're going to try to answer this question
in as much detail as possible. No skipping out on anything.

This is a collaborative process, so dig in and try to help out! There are tons
of details missing, just waiting for you to add them! So send us a pull
request, please!

This is all licensed under the terms of the Creative Commons Zero_ license.

Read this in 简体中文_ (simplified Chinese), 日本語_ (Japanese), 한국어_
(Korean) and Spanish_. NOTE: these have not been reviewed by the alex/what-happens-when
maintainers.

Table of Contents
====================

.. contents::
   :backlinks: none
   :local:

The "g" key is pressed
----------------------
The following sections explain the physical keyboard actions
and the OS interrupts. When you press the key "g" the browser receives the
event and the auto-complete functions kick in.
Depending on your browser's algorithm and if you are in
private/incognito mode or not various suggestions will be presented
to you in the dropdown below the URL bar. Most of these algorithms sort
and prioritize results based on search history, bookmarks, cookies, and
popular searches from the internet as a whole. As you are typing
"google.com" many blocks of code run and the suggestions will be refined
with each keypress. It may even suggest "google.com" before you finish typing
it.

The "enter" key bottoms out
---------------------------

To pick a zero point, let's choose the Enter key on the keyboard hitting the
bottom of its range. At this point, an electrical circuit specific to the enter
key is closed (either directly or capacitively). This allows a small amount of
current to flow into the logic circuitry of the keyboard, which scans the state
of each key switch, debounces the electrical noise of the rapid intermittent
closure of the switch, and converts it to a keycode integer, in this case 13.
The keyboard controller then encodes the keycode for transport to the computer.
This is now almost universally over a Universal Serial Bus (USB) or Bluetooth
connection, but historically has been over PS/2 or ADB connections.

In the case of the USB keyboard:

- The USB circuitry of the keyboard is powered by the 5V supply provided over
  pin 1 from the computer's USB host controller.

- The keycode generated is stored by internal keyboard circuitry memory in a
  register called "endpoint".

- The host USB controller polls that "endpoint" every ~10ms (minimum value
  declared by the keyboard), so it gets the keycode value stored on it.

- This value goes to the USB SIE (Serial Interface Engine) to be converted in
  one or more USB packets that follow the low-level USB protocol.

- Those packets are sent by a differential electrical signal over D+ and D-
  pins (the middle 2) at a maximum speed of 1.5 

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