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[[ De-Escalated Quickly ! OK , I will try to edit it so that my intent is clear ]]

According to this Post , we can use "Dummy" Hardware to make a fake Display.
Such fake Hardware are used in cases where (1) the PC will refuse to Start without attached Displays.
Essentially, (2) we are "tricking" the PC into thinking that there is a Display.

This is all fine. Headless PCs are useful. RDP & VNC can run without Displays connected. Some third Party manufacturers have taken the chance to make fake Displays.

But, (A) why should there be such a requirement of a Display from the PC (or OS) manufacturer ?
In case it is really absolutely necessary, (B) why should it be so easy to circumvent ?

(A) Let us say, it is Mandatory to have a Display (eg troubleshooting or setting the size of resolution) then
(2A) Still, troubleshooting info can be put in text output [[ log file or over network ]]
(2B) User can be given a choice to run without Display by some config file which says [[ -Display=None -res=1024x768 ]]
Then in fact , it is not really Mandatory.

Using Analogy 1, when we ssh to a linux machine to execute certain commands, we might get "stdin: is not a tty" which is "requirement". Still user has the choice to use ssh -t to over-ride that requirement. We should not look to third Party manufacturers to make some fake tty Hardware or Software ( oh , this is just to explain , I know it is not Possible ! )
Here tty is a requirement but not Mandatory.

Using Analogy 2, if OS has Mandatory minimum requirement of 500GB Disk + 32GB ram, it is because the OS installation will require that much Disk Space & OS will run-time require that much ram.
During Installation, OS can check this & exit if necessary.
If we circumvent using some 100GB Disk which reports 500GB Size, Installation is going to ultimately fail.
If we circumvent using some 16GB ram which reports 32GB Size, run-time is going to ultimately fail or crash.
Here it is a Mandatory minimum requirement of 500GB Disk + 32GB ram.

In case we can do without Display, why is the PC or OS checking it ?
In case we can not do without Display, how can the fake Hardware work ?

It case it is really Mandatory, then the fake Hardware would not work. If OS manufacturer thought it was really Mandatory , then it should be made un-circumvent-able.

Prem
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    Its probably just a matter of: it was build with the thought in mind that someone would be sitting behind the computer and for troubleshooting, one would need a display, so why go through all the steps to add support for a headless system? Though I suspect this is more for OSses with a GUI, and not so much for OSses that are textbased. I bet those OSses can be headless. – LPChip Aug 23 '22 at 19:26
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    It’s already explained in enough detail on the other question. Some software may behave differently when a screen is connected or when a screen with a certain resolution is connected. – Daniel B Aug 23 '22 at 19:26
  • If you have to ask why you **shouldn't** use one of these then you are probably not the target audience for them. – Mokubai Aug 23 '22 at 20:12
  • I was not asking why "I" should not use it ; I was asking why OS manufacturers **"InDirectly"** say "all users" should not use it. If OS manufacturers say "oh , it is ok to have no Display ; our OS will boot up just fine !" , there will be no concern & no fake hardware. @Mokubai – Prem Aug 24 '22 at 04:24
  • Is it not Possible that my Commentary is indeed the "correct" answer ? It **may** be a legal requirement to have a Display. @Mokubai , If you hide it , how will others read it (to at least downvote) to say it is wrong or to object to it ? – Prem Aug 24 '22 at 06:50
  • If you must have rambling commentary on what kind of answer you are looking for then put it in the body of your question. – Mokubai Aug 24 '22 at 06:53
  • If I put it in my Question, folks do not read the whole & answer some other Question about using headless systems , RDP , VNC & target audience which are all well known in other other Question. **The more I think about it, the more I am certain that this is a legal requirement, which "users" (not OS makers) can circumvent at their risk.** The rambling in my answer is necessary to Explain the legal aspect , which I might make shorter (or even remove) if it were not deleted. @Mokubai – Prem Aug 24 '22 at 07:06
  • One problem is that you are assuming any one person or operating system is at fault and that the design was intentional. Windows and operating systems tend to want to display things, for that they look for a graphics card, that graphics card looks for a screen to display stuff on. There is no display so the graphics card goes back with an error telling the OS as much, and the OS gets an error about no graphics device that it has no idea how to handle. It *could* handle it, but as 99.999% of PCs have a display it's low on the list of priorities. Then some enterprising company makes this dongle. – Mokubai Aug 24 '22 at 07:07
  • There is no "legal" requirement for computers to have a display. – Mokubai Aug 24 '22 at 07:08
  • I claim there are legal issues why Display is required (but users can disable at their risk) ; you claim there is no legal issue. Who is right ? Who-ever has the Delete Powers , with no way for others to read / respond / agree / disagree. – Prem Aug 24 '22 at 07:16
  • You vaguely allude to legal issues in order to clutch at something more than the simple idea that on certain combinations of hardware and software what you are doing is simply "unsupported" and that no one got around to fixing it. There is no law that states that a PC should have a display and just vaguely saying "maybe theres a law" doesn't make commentary into an actual answer. Legal debates would also be off topic here. – Mokubai Aug 24 '22 at 10:55

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A typical case for a fake display card is that of a headless computer (no display) that one wants to use remotely by VNC or RDP.

Such software relies on sharing the computer's screen, so can't work without a display. This fake makes it possible. There are other cases.

If someone is manufacturing it, it's only because people are buying it, which means that there is a need for it.

harrymc
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  • I have no Doubt that RDP + VNC can work & that the fake hardware is useful. I know why that Exists. I am asking why the OS manufacturers made the situation for that to Exist. If manufacturer had given choice to run without (fake) Display, that market would not exist & RDP + VNC will still work. – Prem Aug 24 '22 at 04:28
  • If OS manufacturers had the capacity to think of and implement every possible use of their OS, there would exist no third-party products. – harrymc Aug 24 '22 at 08:16
  • Yes, they may not have the capacity , but we can see that they always absorb the useful usages. MS Windows did not come with AntiVirus, AntiMalware, telnet or SSH Clients, virtualization, archiving, Speech Processing, tabs in file manager, firewall .... We had to use third Party tools. Now , these are all builtin, though some users may still want to use the third Party tools. – Prem Aug 24 '22 at 09:24
  • To add that comment : If enough users wanted the fake Display to make a big enough market & Hardware Solution was made , surely , OS makers could have taken this to give a Simple Software Solution – Prem Aug 24 '22 at 10:02
  • Well, they don't have the means to do everything, so they concentrate on the big markets, leaving small niche markets like fake displays to other small companies for whom this is worth the effort. – harrymc Aug 24 '22 at 10:05
  • Thanks for engaging in Discussion (1) Here, even a niche market has a very simple solution. (2) More-over it is an annoyance to users who have to buy more hardware. If there was no Display Check, nobody would be annoyed & fake Display would not Exist. (3) I am tending to the thought that Display is mandatory due to legal Issues. If user has Damages (Data loss or Downtime) , because user did not see the Critical Status Messages , OS can not be Prosecuted because OS did give the Warning which went unseen. User has taken the risk by using fake Display. (4) I had elaborated in a Deleted Answer. – Prem Aug 24 '22 at 10:19