Editing Harvard Mark I (section)

==Instruction format==
The 24 channels of the input tape were divided into three fields of eight channels each. Each storage location, each set of switches, and the [[Hardware register|registers]] associated with the [[Input/output|input, output]], and [[Arithmetic logic unit|arithmetic units]] were assigned a unique identifying index number. These numbers were represented in [[Binary numeral system|binary]] on the control tape. The first field was the binary index of the result of the operation, the second was the source [[datum]] for the operation and the third field was a [[Opcode|code]] for the [[Instruction (computer science)|operation]] to be performed.<ref name="wilkes">{{cite book
  |author = Maurice Vincent Wilkes
  |title = Automatic Digital Computers
  |publisher = John Wiley & Sons
  |year = 1956
  |location = New York
  |pages = 16–20<!--   305 pages that's total, not the ones we want -->
  |url = https://books.google.com/books?id=n_oNAAAAQAAJ   <!-- | id = QA76.W5 1956 what is that? -->
  |author-link = Maurice Wilkes
}}</ref>