If a .zip file contains all of the information of the original, just in less space, why does it have to be unzipped to access any of it?
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Imagine you have a book. Now, instead of being in plain English, it is written in shorthand to save on paper. To read the book you would need to read a sentence and then use a dictionary to translate it to plain English. As you can imagine, this would take a heck of a lot longer than just reading a book that is written in English. Now imagine your friend Bob who doesn’t know how to use a dictionary, how is he going to read the book? He could get you to translate it for him as he reads it but that would take even longer. What if the book was a cook book? Would you be able to translate the book quickly enough for Bob to be able to make a recipe from it? Or would the extra time mean that the dish Bob was cooking gets ruined through over cooking?
Now, a .zip file is like a book that has been translated into shorthand to save space but instead of a book it is data and instead of shorthand it is a dictionary that has been made up at the time of zipping the file based on what is in the data (e.g. there is no need for a shorthand version of “a triumphant roar was heard” if it doesn’t appear in the data). A program (e.g. Notepad) is like Bob who doesn’t know how to use the dictionary so it needs someone else to translate the zipped file for it.
There are transparent compression methods used fairly often in computers though. For example, Windows has the ability to compress data in memory so that you can store more data in it and it does this without the knowledge of whatever owns the data – the downside is that the data needs to be decompressed for the program to use it which slows down how quickly the data can be accessed. Windows can also do this for data held in storage (like on SSDs and HDDs) but, again, this slows down how quickly the data can be accessed so it isn’t used by default.
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