It's called "parallel computing" and it has been done. Now, are you a electrical engr. and computing engr.? I ask, because your 1st task is to make a custom connection(buss) to start it all off with. You're better off just using an older "muli-core cpu" already done for you. Google for parallel computing for hits. Here's something I found:
http://www.google.com/search?hl=en&sclient=psy-ab&q=parallel+computing+builds&btnG=
FYI- Those that have done this used similar PCs, like in the same model# whether they be Apple or Power PC or simple IBM type clones, they were exactly alike. They made the connections, all custom repeated and then ran whatever s/w to use it. I don't the peculiars but for you and me, it would be a daulting task. AND no, they didn't leave instructions as to repeating it.
tada -----Willy 
I have two old desktop PCs, and I think there is a way to connect them together and use them as one computer (make the processers work together, the RAM work together, and so on.)
Is this possible? And if so, how?
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