so are all microcontrollers are same to operate in a specific topic? Or are there variants to do a special kind of operation?
It's a bit of a chicken and an egg thing. Microcontrollers like all computers are a non-specific piece of hardware looking for an application.
But yes, some are manufactured for more specific markets.
Generally if we look at PIC chips you will find some are ultra simple. WW2 computers were more complex
The 12F508 is one that jumps to mind. It basically has nothing more than a couple of I/O pins and a timer on board.
While something like the 12F510 which is the same size is packed with features like comparators and A2D converters etc. in the same size chip.
The 16F84A, which everybody loves to remind you it's out of date is one of the best chips to learn on.
It's easy to port code to the newer chips and you do not need to worry so much about checking and setting registers which don't mean much to you.
The 16F88 is like a sooped up version of the 16F84 so it doesn't take long to take advantage of these different or better and cheaper chips.
Same can be said for the 16F877. Another good chip to work with and learn on. But as I've just found out, there is the 16F887 which is probably better.
There's no need for me to rush out and buy some 16F887 chips. I will just use the 877's until they run out.
If you're looking to get into programming PIC chips the next question is what language are you going to use.
Basic, C, Assembler or something else ?
Is there a reason why you've taken an interest in micro controllers or just general curiosity ?