Original silicon from Bell labs.
From the original owner:
My memory is failing, but I do remember purchasing these online from a man that was selling out his dad's estate. He told me his dad had worked at Bell so that was enough for me to take a gamble. The seller had no idea what he was selling. I had only just begun wafer collecting and had no idea the significance of what I'd bought. Bad news is, It took me a couple years to identify these and I had no luck trying to reconnect with the original seller. Good news is, I'm pretty sure this man's father was no ordinary Bell employee and you'll get more than one of his wafers. He had three different types. At first glance the chips look the same, but if you look more carefully you'll see they are slightly different. After studying them, I came to the conclusion that one type was a tested production BellMAC-4, another is a untested prototype with larger RAM and ROM blocks, and the third is a code development chip, missing the ROM block and with some other simple circuitry and extra outside connections in its place. This is not just a wild guess. I used to design microprocessor emulation hardware myself.