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Explain xkcd: It's 'cause you're dumb.
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Refresh Types
The hardest refresh requires both a Mac keyboard and a Windows keyboard as a security measure, like how missile launch systems require two keys to be turned at once.
Title text: The hardest refresh requires both a Mac keyboard and a Windows keyboard as a security measure, like how missile launch systems require two keys to be turned at once.

Explanation

In this comic Randall presents five different levels of refresh operations for web applications. The first three (soft refresh, normal refresh, and hard refresh) are common operations to keep the content in the browser retrieved from the server up to date. The other two (harder refresh and hardest refresh) are fictional operations to perform refresh operations on remote resources. The terms are probably adopted from soft and hard reset operations used to restart broken computers or e.g. smartphones.

Soft refresh

Soft refresh refers to an operation in a web page that requests new information without reloading the entire page. The given example, Gmail, includes a feature that allows users to poll new emails and show it in the inbox interface. It is a command using JavaScript and Ajax to load new contents from the server in the background and only updating necessary components of the page. Since modern web applications doing this also automatically in short time intervals those buttons are mostly needless. In Gmail a user will see a new message instantly.

Normal refresh

The normal refresh is a browser operation that reloads the complete web page, text and other content that has changed since the original load will be updated. The operation can be triggered by refresh buttons in browsers, though it also can be requested using the common keyboard commands as listed by Randall. Many pages -- like the main page at xkcd.com -- don't have a refresh button, but pressing the F5-key after a new comic is released is will be shown in the browser.

Hard refresh

Hard refresh is a less common browser operation that clears any cached files associated with the page before requesting a new copy. Browser caching is a way to store webpage resources locally in order to decrease load time and data transmitted. Hard refreshes are usually used when a webapp has changed in such a way that the cached data is interfering with the proper display of the page. A hard refresh is slower because it forces the browser to download the entire page, but it ensures that the page is displayed as it is currently being served.

Interestingly, hard refresh HTTP request contains special headers (associated metadata) that command all intermediate proxy servers to drop their caches too. These headers can be seen by end application running on the web server, that can choose to reload some data from database and redo some long-running calculations in this case, even though this is not mandated by HTTP standard. In orchestrated environment it may indirectly cause some virtual machines to be rebooted. Rebooting actual physical server upon web page hard refresh is of course not normal, but additional processing may trigger some hardware or operating system bug that will cause exactly this.

Harder refresh

Harder refresh is a joke that extends the existing naming scheme. The joke is that if a hard refresh resets the browser display and cache, a harder refresh should reset the source of the data by cycling power in the data center. Assuming no damage was done, this would reset the memory on the server, erasing any information that had not been written to disk, and setting the server to the state it was in at launch. This would cause considerable downtime, and would be unlikely to help the user at all.

The harder refresh uses six keys, including the non-standard 'HYPER' key, a feature of the Space cadet keyboard.

Hardest refresh

The fifth option, hardest refresh, moves beyond resetting the source of the data and resets the entire internet back to ARPANET, an early military network which was a forerunner to the modern internet. The implications of this are not made clear, but it should be noted that it wouldn't help to fix any problems a user is experiencing in-browser, as HTTP, the protocol by which web pages are sent, was not developed until late 1990, the year ARPANET was decommissioned.

The hardest refresh shortcut uses fifteen keys, including non-standard ones such as Ø and ⏏. (The former is a key found on Norwegian and Danish keyboards, the latter is the "eject" key found on [older?] Mac keyboards.) The shortcut makes amusing comparisons about a shortcut that includes not only the F5 function key, but also the keys for the letter "F" and the digit "5", as well as the similarity in appearance between O, 0, and Ø.

The title text suggests that the inclusion of both the Windows key and Command key in the hardest refresh shortcut is a security measure akin to the Two-man rule, as it would require two keyboards to enter.

Transcript

Ambox notice.png This transcript is incomplete. Please help editing it! Thanks.
Refresh Type Example Shortcuts Effect
Soft Refresh Gmail REFRESH Button Requests update within JavaScript
Normal Refresh F5, CTRL-R, ⌘R Refreshes page
Hard Refresh CTRL-F5, CTRL-⇧, ⌘⇧R Refreshes page including cached files
Harder Refresh CTRL-⇧-HYPER-ESC-R-F5 Remotely cycles power to datacenter
Hardest Refresh CTRL-⌘⇧#-R-F5-F-5-ESC-O-0-Ø-⏏-SCROLL LOCK Internet starts over from ARPANET


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