How can a machine with fixed output for all inputs be considered a Turing machine? From this answer, and the comments that follow:

To clarify, this machine T′ with the fixed output for all inputs is a Turing machine? – Shashank V M


@ShashankVM, Yes, T′ is a Turing machine. – D.W.♦ (When can a deterministic finite-state-automata (DFSA) along with its input sequence be said to be a part of another DFSA?)

From what I understand, a machine with fixed output for all inputs is a Turing machine.
Consider this thought experiment, I have a &quot;machine&quot; which is a wall with a slit through which I can pass a tape in. The &quot;output&quot; of this machine is on the wall, i.e. it is painted on the wall as a fixed string $S$, which for the purpose of this experiment is &quot;Hello&quot;. So no matter what is written on the tape, the output of this &quot;machine&quot; is &quot;Hello&quot;. From what I understand this &quot;machine&quot; is a Turing machine.
Is my understanding correct or am I missing something?
Because I find it hard to believe that this wall with a slit can be considered a Turing machine, when a supercomputer is considered a Deterministic Finite State Automaton.
Also I cannot see how this &quot;machine&quot; can emulate any another Turing machine or do any useful computation.
There's no notion of &quot;can be considered to be a Turing machine&quot;.  Something either is a Turing machine, or it isn't.  There's a formal mathematical definition of what a Turing machine is: https://en.wikipedia.org/wiki/Turing_machine#Formal_definition
I never claimed that just because some process always produces the same output, that process must be a Turing machine.
There might be some confusion about Turing machines vs DFAs.  A computer could be modelled as a DFA (if we treat its memory size as fixed), or it could be modelled as a Turing machine (if we imagine that it's possible to gain more memory; or we just don't care to make use of the fact that memory size is fixed).  These two different ways to think about a computer have different advantages and disadvantages.  I suggest reading Is a PDA as powerful as a CPU? and How many gates until Turing Complete and How does an automaton model a computer or something else? and How does an automaton actually &quot;compute&quot;?, as I suspect they get at the core issue you are struggling with.