It's old, and it was created and sharpened by old people with Unix smudges on their fingers. This is not so much a good answer, as an excuse to indulge myself a

It's old, and it was created and sharpened by old people with Unix smudges on their fingers. This is not so much a good answer, as an excuse to indulge myself and listen to Stephenson for a moment. The file systems of Unix machines all have the same general structure. On your flimsy operating systems, you can create directories (folders) and give them names like Frodo or My Stuff and put them pretty much anywhere you like. But under Unix the highest level--the root--of the filesystem is always designated with the single character "/" and it always contains the same set of top-level directories: /usr /etc /var /bin /proc /boot /home /root /sbin /dev /lib /tmp and each of these directories typically has its own distinct structure of subdirectories. Note the obsessive use of abbreviations and avoidance of capital letters; this is a system invented by people to whom repetitive stress disorder is what black lung is to miners. Long names get worn down to three-letter nubbins, like stones smoothed by a river.