42.zip is a 42 KB zipped file. It contains 16 zipped files, which again contains 16 zipped files, which again contains 16 zipped files, which again contains 16 zipped, which again contains 16 zipped files, which contain 1 file, with the size of 4.3 Gigabytes (GB). So, if you extract all the files in 42.zip, you will most likely run out of space as it ends up with a file size of 45 Petabytes (PB) where 1 Petabyte is equal to 1 million GB or 1,000,000,000,000,000 Bytes. 
42 KB Zipped File 42.zip When Unzipped Make 4.5 Petabytes
Here is the calculation showing how 42 Kilobytes zipped file when unzipped make 4.5 Petabytes (where 1 Petabyte is 1 million GB)
16 x 68719476720 = 1.099.511.627.520 (1TB)
16 x 1099511627520 = 17.592.186.040.320 (17TB)
16 x 17592186040320 = 281.474.976.645.120 (281TB)
16 x 281474976645120 = 4.503.599.626.321.920 (4,5PB)
You might be wondering how can such a large file, be compressed to 42 KB zipped file. This is made possible by the high statistical redundancy of the 4.3 Gigabytes (GB) file as it contains only zeros in needless repetition. Exploiting this statistical redundancy, compression algorithms are able to compress the file data more concisely into a 42 KB ZIP file.
42.zip is also known as zip bomb, zip of death or decompression bomb. It is a malicious ZIP archive file intentionally designed to crash or make unusable the system extracting it. You can download this 42 KB ZIP file 42.zip from www.unforgettable.dk
Don’t dare to extract this 42 KB zipped file 42.zip!!
If I extract it in my system, then what will happen next??
If you extract all the files in this 42 KB zipped file 42.zip, you will most likely run out of your hard disk space as it will end up with a total file size of 45 Petabytes (PB) where 1 Petabyte is equal to 1 million Gigabyte