The book "Computer Architecture: Concepts and Evolution" by Blaauw and Brooks has many descriptions on how instructions got to be the way they did.
The book covers a wide variety of machines, though S/360 is a favorite example. (Blaauw was the main designer of S/360, so it isn't so surprising.) There is a small description of EDIT in section 5.1.3. They trace back to "Store for Print" on the 702. Then explain that EDIT is rarely used by COBOL or Fortran for print conversions, and that it is best that it should be left out of instruction sets. If you like asking questions like that, especially for a variety of different machines, you should get the book. -- glen
