Relay Computer Two

Posted on Feb 5, 2014

The simple relay adder was built using free NOS relays sometime in 2005, but my goal was to someday build a more elaborate one that could run programs but notfill up a room like the early computers. Harry Porter built an incredible 415-relay computer which can be seen at this page: I never thought I`d fully understand how his computer worked, let

Relay Computer Two
Click here to download the full size of the above Circuit.

alone build one. Finally in spring 2007, I gained more understanding of computer systems from a course in college then joked to a friend about using the x86 instruction set for a relay computer to boot up Windows, which would`ve taken several hundred years on a relay computer running on a 50Hz clock. And so the inspiration began. (note: if you want to skip the hardware details of the computer, the pictures and videos are at the end of this page). Seriously, the x86 instruction set is insanely large for a simple relay computer so I created my own instruction set. I looked at Harry Porter`s relay computer design for inspiration and ideas for the hardware. But first, the computer cannot exist without the actual relays. After searching several online electronics suppliers for relays, the lowest price I could find was at $1 per relay so a computer using 200+ relays can become rather expensive. So ebay was the next option and after patiently watching several auctions, a lot of 168 SPDT relays came up and I nabbed it for about $25. A few weeks later, another lot of 100 4PDT relays came up and I won it for about $14. Including shipping costs, the total cost for the 268 relays I purchased from ebay was about $60. So, 268 relays became my limit for the computer design. Obviously, I did not try to copy Harry Porter`s relay computer because it called for 400+ relays, but I borrowed many ideas from his design so I wouldn`t have to...

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