The "dark web" of anonymous and often illegal content not accessible in any way via ordinary web pages and links is often confused with the deep web of all material not accessible to a normal search engine. The dark web is part of the deep web, but only a tiny part of it.
They are good names, and I think it's a shame to confuse them. If you use "Deep web" to describe the dark web instead, as many are doing now - what then should we call the deep web? It needs a phrase to describe it.
Perhaps we need a new word for it as it has got so confused now with the dark web?. Or, try to make a new catchy word for "dark web" that catches on and takes the place of "Deep web" so leaving that free to return to its original use. Mike Siciliano in a comment suggests "Dark net" for "Dark web" might work.
As a simple example, for images - then NASA has all the images every taken by the Mars Reconnassance Orbiter available here: Images - Mars Reconnaissance Orbiter
But most aren't accessible to Google just because there are too many of them for them to put up images of them all in individual pages. And many are of boring regions of Mars that look much alike to non specialists.
To find most of the photographs you have to search - e.g. give the latitude and longitude of the area of Mars you are interested in. Then it will give you a succession of dates - all the dates when it was photographed. None of that is in google images, so this is an example of the deep web.
Google could only index them by doing the same thing, entering all possible locations on Mars into that search form, then accessing the images for all the possible dates until it accessed all the photographs.
There are now some image
Another example, Digital Library of Free Books, Movies, Music & Wayback Machine let's you access web pages from any historical date since the archiving project started. E.g. here is wikipedia in 2003 Main Page - Wikipedia
That won't appear in google because the only way to get to it is to type the wikipedia website url into the archive.org search engine.
So the deep web is huge, many times larger than the searchable web. Apart from things only available through forms like that, it also excludes any pages that website owners decide they don't want to make searchable. E.g. if I put up a page and don't want it to appear in google, I just edit my robots.txt file to exclude it. That then makes it part of the deep web.
It also includes any pages that the search engines just haven't reached yet. Not sure what the status is now but used to be anyway that in large websites, if your content was only accessible some way into the site, needs many clicks to get to it, that - unless someone else linked to it, google wouldn't bother indexing it.
Or new content, you just made a new website and nowhere links to it yet, and you've only told a few friends by email - then your website is in the deep web until you tell the search engines about it, or someone in an indexed site links to it and the search engines catch up on that.
Or content behind paywalls.
Or password protected content. For instance if you access your bank account online, the online page with your bank statement is visible to you only - so is part of the deep web. You'd not be well pleased if the bank served it up to the general public or to search engines :).
The "Dark web" however consists only of material that is not accessed via normal urls at all. You can't find it by clicking through links or using web forms to search it or by entering passwords to visit password protected sites or by using a secure https connection.
You have to download special software to get to it. Or access it via a website that has that software installed onto it.
You can search some parts of the deep web (including the dark web) using specialized browsers, see
Deep web (search) - Indexing methodologies
But some of those don't exist any more. E.g. DeepPeep no longer exists for lack of funding apparently.
More listed here
10 search engines for the hidden web : Off-Topic
but again many of those may no longer exist.
Here is a page to access scientific articles on several different deep web search engines: Page on science.gov
For more on this:
Dark Web
Deep web (search)
They are good names, and I think it's a shame to confuse them. If you use "Deep web" to describe the dark web instead, as many are doing now - what then should we call the deep web? It needs a phrase to describe it.
Perhaps we need a new word for it as it has got so confused now with the dark web?. Or, try to make a new catchy word for "dark web" that catches on and takes the place of "Deep web" so leaving that free to return to its original use. Mike Siciliano in a comment suggests "Dark net" for "Dark web" might work.
As a simple example, for images - then NASA has all the images every taken by the Mars Reconnassance Orbiter available here: Images - Mars Reconnaissance Orbiter
But most aren't accessible to Google just because there are too many of them for them to put up images of them all in individual pages. And many are of boring regions of Mars that look much alike to non specialists.
To find most of the photographs you have to search - e.g. give the latitude and longitude of the area of Mars you are interested in. Then it will give you a succession of dates - all the dates when it was photographed. None of that is in google images, so this is an example of the deep web.
Google could only index them by doing the same thing, entering all possible locations on Mars into that search form, then accessing the images for all the possible dates until it accessed all the photographs.
There are now some image
Another example, Digital Library of Free Books, Movies, Music & Wayback Machine let's you access web pages from any historical date since the archiving project started. E.g. here is wikipedia in 2003 Main Page - Wikipedia
That won't appear in google because the only way to get to it is to type the wikipedia website url into the archive.org search engine.
So the deep web is huge, many times larger than the searchable web. Apart from things only available through forms like that, it also excludes any pages that website owners decide they don't want to make searchable. E.g. if I put up a page and don't want it to appear in google, I just edit my robots.txt file to exclude it. That then makes it part of the deep web.
It also includes any pages that the search engines just haven't reached yet. Not sure what the status is now but used to be anyway that in large websites, if your content was only accessible some way into the site, needs many clicks to get to it, that - unless someone else linked to it, google wouldn't bother indexing it.
Or new content, you just made a new website and nowhere links to it yet, and you've only told a few friends by email - then your website is in the deep web until you tell the search engines about it, or someone in an indexed site links to it and the search engines catch up on that.
Or content behind paywalls.
Or password protected content. For instance if you access your bank account online, the online page with your bank statement is visible to you only - so is part of the deep web. You'd not be well pleased if the bank served it up to the general public or to search engines :).
The "Dark web" however consists only of material that is not accessed via normal urls at all. You can't find it by clicking through links or using web forms to search it or by entering passwords to visit password protected sites or by using a secure https connection.
You have to download special software to get to it. Or access it via a website that has that software installed onto it.
You can search some parts of the deep web (including the dark web) using specialized browsers, see
Deep web (search) - Indexing methodologies
But some of those don't exist any more. E.g. DeepPeep no longer exists for lack of funding apparently.
More listed here
10 search engines for the hidden web : Off-Topic
but again many of those may no longer exist.
Here is a page to access scientific articles on several different deep web search engines: Page on science.gov
For more on this:
Dark Web
Deep web (search)
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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