The /proc file system first made its way into some Unix operating systems (like Solaris) in the mid-1990’s, promising to give users more and easier access into the kernel and to running processes. It was a very welcome enhancement — looking and acting like a regular file system, but delivering hooks into the kernel and the ability to treat processes as files. It went well beyond what we could do with ps and other common commands for examining processes and the system they’re running on.
When it first appeared, /proc took a lot of us by surprise. We were used to devices as files, but access to processes as files was new and exciting. In the years since, /proc has become more of a go-to source for process information, but retains an element of mystery because of the incredible detail that it provides.
From: Network World