I just finished reading Walter Isaacson's Innovators and on page 350 there is a quote from Steve Wozniak recalling things he learned from the March 1975 Homebrew Computer Club meeting:
A person at the meeting passed around the specification sheet for the new Intel microprocessor. "That night, I checked out the microprocessor data sheet and I saw it had an instruction for adding a location in memory to the A register," he recalled. "I thought, Wait a minute. Then it had another instruction you could use for subtracting memory from the A register. Whoa. Well, maybe this doesn't mean anything to you, but I knew exactly what these instructions meant, and it was the most exciting thing to discover ever."
Referencing the book, Intel started selling the 4004 microprocessor in 1971. By definition, I thought a microprocessor has to have registers, so did they just add functionality to the new 1975 microprocessor? Do you believe he was referencing the Intel 4040 microprocessor that came out in 1974? Also, does adding and subtracting memory allow arrays in RAM to be indexed in O(c) / constant time? Is that the significance or are there even more layers to this tale?