Sorry to burst your bubble, if you think there's such a thing as unlimited and instant you're sorely mistaken.
It might've been fast in simple cases compared to the alternatives, but there's no two ways about it that all computation takes time, and you can make tradeoffs where you cache more and compute less, but that's it.
It's not instant and unlimited. It's Limited and fast, or more limited and faster, or more ram and faster, or more data and slower.
Stop bending semantics to fit your binary view point.
Instant in this case means you move the brush and it distorts as you move the brush. No parallax, no beach ball waiting for it to do the computation. It happened as you moved it. It was instant. Even with brush sizes the size of the image you were using.
It had unlimited undo. It had unlimited layers. That's not an arguable point.
We write software for humans. The same humans who can't tell the difference between instantaneous events and events separated by less than a few milliseconds. The same humans who won't be around for long enough to recognize the difference between a really large number of events and an unlimited number of events.
So, by all means, continue to write software for those ideal beings that live in a world of comprehensible instantaneous and unlimited events, but you'll find that most people on this forum are operating under a different assumption.
Don't take words literally. Instant in this context means what jawngee said, that it was so responsive to the degree that people conceived it as instant. Awesome. Layers were unlimited meaning you could add as many as you want. Undo operations were unlimited meaning you could work on it for 10 hours straight and undo to the point it was before you started working on it. I believe that's what everyone gets from these words, except you.
It's not like people will think it's unlimited for real, there's no such thing.
It seems to me you are having problems interpreting words in context.
EDIT: I mean, if he said you could have 8K undos, or 8K layers and the response time is <15ms would that make you feel better? Does it make a difference?
It's just not a useful factor of the conversation if it is actually instant or if it was just so fast people felt it was instant. I could spend years getting the frame rate of one of my games from 59 to 60 per second, but it isn't a meaningful difference.
In and Out of context, there's no such thing as instant and unlimited. There might be fast, and there might be a lot, and there might be faster and more than you usually need. But I repeat, stop claiming utter nonesense.
I think you don't know what unlimited means. It doesn't mean "infinite" - it means - there was no limit placed on it. Sorry, but you didn't understand that word, plain and simple, and now you really have created an ass-thread for yourself.
Second: "instant". It means, quite literally, "an infinitesimal or very short space of time; a moment". So, calling software "instant" - this is perfectly valid.
I think you should go back and re-read your thread with those two definitions in mind, and figure out who you need to apologize to for being ignorant ..
They're the same image sizes we use today. And it was instantaneous, or relatively so in comparison to Photoshop 3 - which couldn't edit the images at all due to size. We would have to use a plugin to work on parts of an image most times.
There are other limits you'll hit long before you'll hit the computers raw storage capabilities. CPU <-> RAM access takes time, CPU <-> Disk access takes ages compared. As your dataset grows you'll exhaust page caches, cpu caches, etc. and things start to slow down disproportional to access (twice more data is more than twice as slow). All modern computers have more RAM and Disk space than you can use simultaneously in a usable (human term) time frame.