RC2 returns for a comparison.

Day 22

     Today we will be looking at the ALU in some depth but with a focus on the differences between the ALU logic in Harry porters computer and the Relay Computer Two. On the surface they have many similarities however the differences begin with component selection Harry uses a 12V ice cube type 4PDT relays while RC2 uses both 4PDT and SPDT relays with  much lower power capability. While this is a small difference it is the first of many that allow for a much smaller, faster and more robust CPU, however it comes at the cost of needing much more in the way of support materials and memory. while this is a better representation of a modern CPU it does little to showcase the beautiful simplicity of the original designs of the 40's, though, that is not the purpose with RC2. In the case of the Harry Porter computer or my own the focus is instead on the theory and functional operation without thought given to speed or complexity but instead to understandability.

     I am going to spend some time breaking down these differences as I see them and where they each have strength and weakness. To start with the ALU itself. First looking at the registers instead of using a pair of NOT gates to time out the delay between the LOAD and SELECT commands allowing for the HOLD line to be powered or cleared as needed RC2 uses a single SPDT relay and a 10uF capacitor to do a similar job given the power needs of the smaller relays this is potentially more effective and definitely more simplistic. However, it comes with the disadvantage of time in the larger relays of the HP computer as these relays consume more power even if at a lower voltage therefore this design lacks scalability while the HP design will work for even the smaller components.

A word on my comparison, I think both of these computers are utterly fascinating Harry's computer is a great teaching and demonstration aid and showcases the old school power that computers had while the RC2 shows just how complex and amazingly fast they are capable of being. so throughout this comparison do not get the impression that I don't appreciate the RC2 or think it inferior. It is just different and not the direction I am going. The RC2 is amazing and the goal of loading windows with it is quite lofty and rather neat and I'm intrigued and will be reading much more extensively on it but it is not quite my goal so don't judge it or me to harshly on that.