Microprogramming: History and Evolution - Edwardbosworth.com
Microprogramming: History and Evolution - Edwardbosworth.com Microprogramming: History and Evolution - Edwardbosworth.com
Wilkes’ Motivations ―As soon as we started programming, we found to our surprise that it wasn’t as easy to get programs right as we had thought. … I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs.‖ After his visit to the United States, Wilkes started to worry about the complexity of the control unit of the EDVAC, then in design. Here is what he wrote later. “I found that it did indeed have a centralized control based on the use of a matrix of diodes. It was, however, only capable of producing a fixed sequence of eight pulses—a different sequence for each instruction, but nevertheless fixed as far as a particular instruction was concerned. It was not, I think, until I got back to Cambridge that I realized that the solution was to turn the control unit into a computer in miniature by adding a second matrix to determine the flow of control at the microlevel and by providing for conditional microinstructions.” In other words, have the control signals emitted by a smaller computer that is controlled by a microprogram. The advantage is that the control unit of this smaller computer is extremely simple to design, test, and understand.
A Diode Memory A diode is a one way current gate. It causes current to flow one way only. Specifically: For current in one direction, it offers almost no resistance For current in the opposite direction, it appears as a very large resistance. A diode memory is just a collection of diodes connected in a matrix. Follow the current paths. This shows the contents of each word. This is a classic ROM.
- Page 1 and 2: The Evolution of Microprogramming I
- Page 3 and 4: Design of the Control Unit There ar
- Page 5 and 6: How Does the Control Unit Work? The
- Page 7: Maurice Wilkes Maurice Wilkes worke
- Page 11 and 12: Early Interest in Microprogramming
- Page 13 and 14: Microprogramming is Taken Seriously
- Page 15 and 16: The Microprogram Design Process Her
- Page 17 and 18: Benefits of Microprogramming As not
- Page 19 and 20: Side-Effects of Microprogramming It
- Page 21 and 22: Microprogramming and Memory Technol
- Page 23 and 24: The IA-32 Control Unit In order to
- Page 25: References (Davies, 1972) Readings
A Diode Memory<br />
A diode is a one way current gate. It causes current to flow one way only.<br />
Specifically: For current in one direction, it offers almost no resistance<br />
For current in the opposite direction, it appears as a very large resistance.<br />
A diode memory is just a collection of diodes connected in a matrix.<br />
Follow the current paths. This shows the contents of each word. This is a classic ROM.
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