Building a 6502 computer: Episode 4, binary and hexadecimal (8 bit, apple, acorn, atari, commodore)

[@MikePerigo]

Nicely summarized but at 12:10 you mentioned that 65535 is usually called 64k without saying why. 10 bits can specify 1024 values. When digital computers were first produced memory was so expensive that it was rare to have more than a few thousand bytes available and since 1024 was so close to 1000 it was convenient to use the standard prefix system used for decimal numbers. Later on when more storage was available marketing decided to add up all those extra 24s to make their specifications look better than their competitors. Eventually this caused so much confusion that a new prefix system was created especially for large binary values en.wikipedia.org/wiki/Binary_prefix . Similarly you then jump to hexadecimal without any mention of octal which was used extensively in computing until hexadecimal took over. Early computers did not use standard sizes for data widths and multiples of 3 bits were more common than 4 bits. The big problem with octal is that it can easily be confused with decimal when written down and hexadecimal much less so. Of course to cover this fully you would have had to double the length of this video :)

[@XTronical]

Thanks, yes I did script the 64k bit you mention then cut it out for brevity. I didn't do octal as it will never be used going forward. I'll pin your comment as it has such good detail.

[@knghtbrd]

What's absolutely infuriating to me as a retro hobbyist sort of person … hex decoders don't exist. Why no exist? Because while some people do want BCD decoders (mostly to replace old chips), we're the only real audience for a hex decoder. And it doesn't make sense to retool for making the BCD decoders have the extra transistors to make them work as hex decoders, even if inputs from 1010 to 1111 are undefined. Hex decoders DO exist as pulls or old stock. But I'd never want to use them because if I design something that uses them and it becomes popular, I'm creating a strain on the supply of cheap parts that are cheap because almost nobody wants them. (Or more strain on not so cheap parts everyone already wants…)

[@MikePerigo]

@@knghtbrd One alternative that you could consider using is an EPROM. I have no doubt that the smallest you will find will be massive overkill but I suspect it will be cheaper than the alternatives except for a matrix of diodes.

[@brianmurphy4702]

An excellent intro!!! Love your thorough descriptions. Am currently designing and building a super KIM 1 using a real 6502 but replacing all external signals and emulating memory all via an arduino MEGA. All GUI via an LCD/Touch on an RPI that sends commands and receives 6502 data & output signals from the MEGA. On the RPI driving the super "KIM-1" interface with Python 3. Observing your build gave me some additional ideas. Thank you.

[@XTronical]

That sounds fascinating

[@gartmorn]

Enjoying this series and hope it’s continuing? Great learning experience!

[@XTronical]

Yes it is, next video release is this series. I like to mix up what I put out as not everyone likes a particular thing and if I do to much in a row you notice drop off in subs. Thanks for the feedback.

[@gartmorn]

@@XTronical no probs! I was just checking! The series is pitched at the right level and is ideal for those wanting to learn how computers work! I have read up on it but it’s still good to see it ‘hands on!’

[@knghtbrd]

It doesn't matter if this stuff is "too basic", it's worth having on in the background just in case something strikes you as "wait a minute, I forgot that…" Even if it doesn't, it hurts nothing to go over the basics again. Teachers call the idea of using stuff you already know long after you've learned it "distributed practice", and it's important to long-term mastery. Or even to refreshing long-term mastery to keep it current. There's also a specific problem that affects folks like me: We get this stuff. We've always gotten it. It came naturally from a very early age. We were "prodigies". We were "experts". We didn't have to learn it all from first principles… Do you realize what that means though? It means we never learned it! Which means if and when we encounter something we don't just already know how to do … we won't know how to do it, and we won't know how to figure out how to do it. People like me tend to be lazy. Yeah yeah yeah I already know that. Oh but I don't know _that_ … and it seems like a lot of work to figure it out. I'll do that later. If later ever comes. I'm not saying anything in this video's going to serve as a hang-up for me. Not the stuff in this video, but stuff you might cover down the line that I'd be tempted to skip, sure. So I will consciously choose to skip nothing, including the inevitably necessary discussion of boxes containing each a very small piece of information for those who don't understand memory at a low level.

[@markgreco1962]

Thank You very much

[@jingjinghuang5538]

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