system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How does file compression work? (.rar, .zip)
gpt
Ok, say you have some file whose content is (way simplified) AAAAAAAABBBBBBBBCCCCCCCCDDDDDDDD.  This takes 32 characters to represent.  Compression works by compressing it into 8A8B8C8D.  This takes only 8 characters to represent.  This is an incredibly simplified compression algorithm though.  Most work by replacing common strings (lets say "the") with one character like 'a'.  They must also append a decompression dictionary (because the most common word in one file isn't the same as another) which tells winzip/winrar how to decompress the file.  This is why you can never get a file to be smaller than a certain size, no matter how much you compress it.