My nephew who reads in first standard was reading a book on basic introduction to computer. It had a line "The Computer has four basic parts", but to my ear "the computer" sounded weird. I think the article should be "a computer". I think "the" make a computer particular to the discussion which is not true here. A general computer has four basic parts, it is not restrained to any particular computer. So am I correct in this thinking?
A speaker marks a noun phrase as definite when they assume the listener will be able to identify what the noun phrase refers to.
So, can you identify what it refers to? Yes. It refers any of the set of computers in general; the particular referent does not matter. We can say that it represents a prototypical computer, if we like.
Using a definite article for prototypical objects or events is a special case of a more general principle: you can use a definite article for a set of objects or events when the particular referent is irrelevant. The following examples are from Birner and Ward 1994:
Somebody left their shopping cart outside here where it could roll into a car. As a good citizen, I'll take it inside. I'll only be a minute; I'll just leave it up front near the cash register.
There are likely a number of cash registers, and the definite article could refer to any one of them, since the particular referent is irrelevant. It doesn't assume that the listener can identify any of them uniquely. (Uniqueness is not part of the definite article's job description, although a rule stated in terms of uniqueness works fairly often.)
Here are a couple more examples of non-unique uses of the definite article, in which the particular referent does not matter, also taken from B&W:
[To spouse, in a room with three equally salient windows] It's hot in here. Could you please open the window?
[Hotel concierge to guest, in a lobby with four elevators] You're in Room 611. Take the elevator to the sixth floor and turn left.
But when it matters what the referent is (a particular computer, or a particular window) the definite article no longer works:
[In a room with three equally salient windows] Next week I'm going to start redecorating the room. #I'll start by replacing the window.
Here, the # symbol means that the definite article is "infelicitous". It's grammatical, but it's inappropriate in this context because the particular referent does matter, unlike in the earlier example.
(Let me emphasize that "this context" here means the stuff in italics: in a room with three equally salient windows. It would be fine, for example, in a room with one window, or if it's otherwise obvious from context which window the speaker is talking about.)
The prototypical usage is simply an example of this principle. Rather than a set of three cash registers, a set of four elevators, or a set of three windows, the computer refers to any of the set of all computers. Since the particular referent is irrelevant, the definite article can be used to refer non-uniquely to any member of this set.
The short answer is that the can be used for any object where there is no ambiguity about which object is in question:
You must switch off the computer before you go to bed
And also when talking about the archetypal object (i.e. the object in general).
The triceratops is interesting not only because of its size, but because of its rhinoceros-like horn.
With most of the scientific inventions we use the. No matter whether or not it's specific to one computer or telephone.
The Computer, the telephone, the internet and so on.
You may further read about the same here -The Mayfield Handbook of Technical and Scientific Writing