All web resources, if accessed via HTTP protocol, send a specific server status message that tells about its current state and errors affecting its normal operation, if there are any. Those are divided into five lists that are marked by the first digit in the number. And any 1xx status code is in the list of messages that contain info that tells the current operation status without any severe errors. Sometimes 1xx responses contain details about slow loading or procedural issues, and all of such messages are background, invisible for client-side (user).
100 Continue Status Code
If you do something and see a 100 status code, it usually means nothing serious - it actually indicates processing delay and occurs mainly in situations when the server is heavily loaded. Basically, this code is about the fact that something is slowing down the normal operation and there will be a slowdown in loading on client-side.
Speaking in technical terms, status code 100 or ‘Continue’ response tells the webmaster that the request was successfully delivered without severe issues, but with noticeable slowdown. Although, the slowdown is obviously lesser than it is for a time-out message to appear. And if client-server connection was not severed and is stable, this will be fixed on its own after a few repeated attempts containing the Expect header inside of it.
101 Switching Protocols Status Code
A message with 101 status code is literally what it says - the request was accepted during protocol switch and it will be handled after a repetition. This notification message is rarely encountered by users, and it contains nothing serious, because those usually appear after the scheduled HTTP protocol update on the server.
If we speak about it from a technical perspective, 101 response code tells webmasters that the request delivery was accepted successfully and it was accepted, but the update was required by the server in the reply to it. Therefore, it needs a repetition containing the Upgrade web header in it to proceed. Basically, in such rare cases when the update messes up some client-side requests, the server generates its own responses containing the same header due to protocol update mismatch.
102 Processing Status Code
Actually, status code 102 is the opposite of the 100 one. Basically, it notifies that the client's request actually causes the excessive load on the server and therefore causes slowdowns and slowly loading content. It rarely appears, mainly when data and media on the server are oversized and cause issues.
From a technical standpoint, an http status 102 shows up when it takes 2000 milliseconds (2 seconds) or more for the server to proceed with the reply to the user's actions. Basically on the edge of the timeout notification conditions. Also, most cases of this situation are caused by a request with the Depth web header. Therefore, it’s more common to encounter a timeout code message than this particular one.
103 Early Hints Status Code
This code message appears when the client and the server use mismatched parameters for content loading and the former can’t decide what data to fetch from the latter preemptively. The 103 response code was introduced in 2017 as a way to inform webmasters about issues with preloading files (don’t confuse it with caching).
Technically, status code 103 is showing when preloading was not set up properly by the webmaster and the final result that user fetched in the response is not matching the result that matches the pre-configured setup. Actually, as its text says, this is about the so-called ‘early hints’ web parameters that should be configured properly.
During the time of Internet existence, IETF introduced a wide variety of codes to cover all web-related issues for users and webmasters. 1xx codes are ones that represent minor situations not seriously affecting user experience. And you can always consult with IETF databases about various HTTP codes.
What does 100 Continue mean
Basically, this message tells about the server suffering under heavy load that causes slowdowns in processing. In other words, all that it says is that it will take some time to load requested data, but not to the point of timeout.
What does 101 Switching protocols mean
Rarely occurring reply that tells that server operates precisely as it should, but is currently under HTTP update maintenance. Therefore, the client needs to repeat the request with newer protocol version.
What does 102 Processing mean
This reply tells that the data or files are too big and the server needs more than 2 seconds to proceed with loading. It’s an alternative to time-out, basically.
What does 103 Early Hints mean
A support message for webmasters that basically tells that the preloading parameters for content needs to be fixed and adjusted or some files have no specific marker for preloading despite being listed for it.