I have gone deep into my archives to further research this question. The earliest book that I could find that uses all three terms is
Operating Systems by Harry Katzan Jr published in (I'm dating myself here) 1973. The book heavily focuses on IBM operating systems since IBM dominated the market in those days.
First, the word "process" does not even get an entry in the index. Where we would use "process", this book uses "task".
In Chapter 5
Evolutionary Development of Operating System Technology, we learn that IBM first broke the "one program at a time" mold when it introduced SPOOL. You will love this quote...
Quote:
The term Spooling was derived from the acronym SPOOL (Simultaneous Peripheral Output On Line) which obviously refers to the process of computing and doing output concurrently.
But anyway Spooling was the first example of
multiprogramming. The computer could run one user written task and it did something else. But the "else" was limited to spooling and few other os supplied utility programs.
Multitasking was the next step where the OS could actually run two or more user written tasks at once.
And
multiprocessing is indeed two or more cpu's in one system. I too used to use multiprocessing to mean multiple processes, but I stopped when real multi-processors came along. It's kinda like the way the terms "microcode" and "firmware" got carelessly used.