17

This is kind of a difficult question to phrase since the Apple 1 wasn't really that well adopted of a platform - under 200 of them made and mostly abandoned by the company within 2 years. That being said, it did have an interesting feature of being able to run with either a 6502 or 6800 CPU.

Looking at the boards, I was always curious about the "6800 Only" markings on the silkscreen and had read something about how you could swap out the 6502 for a 6800 if you so desired. Going through the Apple 1 registry, I can see only one example of where someone actually installed a 6800 chip. Interesting enough, the areas of the board that were "6800 only" are only partially populated, but I digress..

So what I'm really trying to ask is why would Woz have designed this alternate processor capability, what would have been the reason for using the 6800 and what (if any) software is known to have ever existed for the alternate setup?

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    When Woz was laying out the Apple I, did he have enough processors in hand to populate them all? Perhaps the 6800 spot was a contingency plan in case there was never a second production batch of 6502s. – supercat May 10 at 13:40
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    Maybe the solution here is for someone to ask Woz directly. It's possible that he was originally targetting the 6800/6501 processors (which were socket-compatible), but then when MOS Technology was forced to drop the 6501 due to a lawsuit from Motorola, Woz switched to the 6502. Maybe the 6800 logic was left behind simply because the work was already done by the time the decision to support the 6502 was made. Or maybe it was a hedge in case the 6502 turned out to be a market failure. – Ken Gober May 10 at 13:50
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    Was there ever any real use of a 6502-based Apple I? I guess most of these were not for "real use", but rather for tinkering around. – tofro May 10 at 16:01
  • @tofro: I wonder how much tweaking would have been needed to make the Apple I more useful? Remove the cursor control logic, perhaps using that shift register bit as an attribute control, add an I/O port to sample the state of some video counters and a function to assert RDY until the next scan line/refresh cycle, and add an I/O port address that would unconditionally stuff a data-bus byte into the shifter. The code necessary to update the screen would become more complex, but an "update line" function would be able to copy 40 characters from ZP onto the screen in a single frame time. – supercat May 10 at 17:35
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    @tofro It's well known that Woz gave the very first Apple 1 to Liza Loop for her Computer learning centre, and after some difficulties it was used to teach BASIC classes. I'd say that's quite useful :) (on the other hand, in 1976 microcomputers, especially basic ones, were a solution looking for a problem) – Raffzahn May 10 at 17:36
31

At the Homebrew Computer club in Palo Alto, California (in Silicon Valley), Steve Wozniak, a 26 year old employee of Hewlett-Packard and a long-time digital electronics hacker, had been wanting to build a computer of his own for a long time... He looked at the Intel 8080 chip (the heart of the Altair), but at $179 decided he couldn’t afford it...

Another chip, the Motorola 6800, interested Wozniak because it resembled his favorite minicomputers (such as the Data General Nova) more than the 8080. However, cost was still a problem for him until he and his friend Allen Baum discovered a chip that was almost identical to the 6800, while considerably cheaper. MOS Technology sold their 6502 chip for $25, as opposed to the $175 Motorola 6800. Wozniak decided to change his choice of processor to the 6502 and began writing a version of BASIC that would run on it... When his BASIC interpreter was finished, he turned his attention to designing the computer he could run it on. Except for some small timing differences, he was able to use the hardware design he had earlier done on paper for the 6800.[1][2]

However:

Steve Wozniak had tested the clock circuit but had not tried it with a real 6800 (In fact I received an email from him confirming this. The Apple 1 PCB was designed for either a 6502 or 6800 but only the 6502 was ever used).[3]

Sources:

  1. Weyhrich, Steven. "The Apple-1." Apple II History: The Story of "The Most Personal Computer!" Accessed 2019-05-10 from https://apple2history.org/history/ah02/
  2. Moritz, Michael. The Little Kingdom. New York, William Morrow and Company, Inc, 1984: 124-127.
  3. theamazingoperaman. "Apple 1 World First? Running a 6800 processor on the Apple 1!" Accessed 2019-05-10 from https://www.youtube.com/watch?v=ag6pWUhps7U
2

[Caveat: This question asks for opinions and guesswork]

The 6800 was a well proven and widely avaible CPU, while the 6502 was brand new with an unclear future. More important, there was next to no software and no information beside the manuals available, while the 6800 already had a reasonable repository of information.

As a result, it was a sensible decision for a startup to make their design to work with either. 6800 for people wanting to use it in a known/existing scenario and 6502 for more adventurous hobbyists - usually with lots of time to write their own software and as well cash strained, making the 6502 choice quite appealing.

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    "it was a sensible decision for a startup" Wasn't the Apple I design done before Apple was founded? ISTR that the design was done, some people showed interest, and only then was the company started in order to sell it. – a CVn May 12 at 18:31
  • @aCVn Well, the Apple 1 (not I) was designed before Apple was incooperated (1.4.76), but isn't it a core point of a startup to have a product idea before aquiring money - which as well was done before registering the company. Starting from sellign his VW bus and talking a chip dealer in giving them 30 days credit all the way to Mike Makulas 250 grand. In addition, the first sales contract (from Byte Shop) was aquired as well before, as this order of 50 units where the base to convince the chip broker to give a credit line in the first place. All before April 1st. – Raffzahn May 12 at 22:18
  • From Wikipedia: "After building it for himself and showing it at the Club, he and Steve Jobs gave out schematics (technical designs) for the computer to interested club members and even helped some of them build and test out copies. Then, Steve Jobs suggested that they design and sell a single etched and silkscreened circuit board—just the bare board, with no electronic parts—that people could use to build the computers." It was 100% designed and built as a HOBBY, with absolutely ZERO intention to make any money. Only after seeing that it was popular did they try to sell it. – Shane May 14 at 1:29
  • Well, @Shane, I guess you're right, I should no longer talk to people involved, read their writings or worse read books (like Steven Weyhrich great book) or specialized sites when all I need is a look at a paragraph of a much mangled Wiki entry with the slightest bit of knowledge. As well, thank you for explaining that schematics are technical designs. I always wondered. So please be forgiving to someone carrying the crux of micros for such a long time. – Raffzahn May 14 at 9:09
  • The 6800 was released to the general public in November 1974. 6502s were being sold at Wescon in September 1975, only ten months later, and one of its designers was someone who had worked on the 6800 (albeit his major work at Motorola was on the peripheral chips such as the 6820 PIA). And of course this was the first crop of 8-bit microprocessors. So no, I don't think that the 6800 would have been considered significantly more established. – Curt J. Sampson Aug 29 at 23:24

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