A man named Harry Porter built his own computer from scratch, using mechanical relays. http://web.cecs.pdx.edu/~harry/Relay/index.html
He did use an SRAM chip for the 32K of memory. Building that much RAM from relays would've filled much of his house.
"I am endeavoring, ma'am, to construct a mnemonic circuit using stone knives and bearskins."
August 1st, 2nd, 3rd, 2014
"I am a machine. I am a weapon of war. I am a destroyer of life in the service of life, the sword and shield of my human creators." Bolo Invincibilus
, Mark XXIII, Model B (Experimental) 0075-NKE "Nike".