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Comment by sunday_serif | Hacker News Reader

True enough, but having designed a “fantasy cpu” gives you a better frame of reference for understanding the more complex features of a cpu (privilege levels, memory segmentation, virtual addresses, cache hierarchy, etc.)

I often feel like those who haven’t done the exercise of understanding the ISA of a “fantasy cpu” have a really hard time understanding those more advanced features.

I guess all I am saying is that learning the “fantasy cpu” still has value even if everything else in the real world is more complex.

Walking before running and all that.

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I've been doing some planning for a 24-bit fantasy CPU, my plan is to make it pretty baroque. For instance it has some instructions to do things like unpack UTF-8 strings into chars, do alpha compositing, etc. The CPU part looks like a strange mainframe that didn't quite get built into the 1970s and it is coupled to a video system that would make a Neo-Geo blush.

“Neo Geo[a] is a brand of video game hardware developed by SNK.

It was launched with the Neo Geo, an arcade system (called MVS) with a home console counterpart (AES). Games on the Neo Geo (MVS and AES) were well received and it spawned several long-running and critically acclaimed series, mostly 2D fighters. Later, SNK released the Neo Geo CD, a more cost-effective console with games released on compact discs, which was met with limited success. A new arcade system, Hyper Neo Geo 64, was released in 1997, but it did not fare well. SNK also released a handheld console under the brand, the Neo Geo Pocket, which was quickly succeeded by the Neo Geo Pocket Color, which have been given praise despite its short lifetime.

SNK encountered various legal and financial issues resulting in a sale of the company in 2001. Despite that, the original Neo Geo arcade and console continued receiving new games under new ownership until 2004. The Neo Geo brand was revived in 2012 with the release of the Neo Geo X[1] handheld. Since then, a number of other Neo Geo products have been released based on the original Neo Geo.”

— Wikipedia

Seems to be from about 30 years ago in the 1990s.

I just realized that people like me that know all about the Neo Geo are actually in the minority in the world. It's easy to forget what is and isn't common knowledge.

That's amazing. I'm a fan of the Beat-them-up games the Neo Geo brought from the arcade. Do you have any write-ups?

Neo Geo was unforgettable. Anyone who could afford one was a legend.

Yeah, I heard it was very expensive that a joke said that "only kids with divorced parents get one".

Forget advanced features... Without understanding a CPU it's easy to never really understand pointers, and without pointers, it's hard to understand lots of data structures.

I was easily 12 months ahead of other students in my CS education because I learned 6502 assembly in high school. I wish all CS courses started with "make a VM".

This is very true. I had tried learning C multiple times but pointers were always kind of hard. I kind of understood them but not really. I later spent a lot of time making an OS in assembly for my homebrew 6502 computer, and after that pointers made so much sense. It actually took me a little while to realize that these addresses I was passing around were pointers, and I had started to understand them without realizing it.

I don’t get this take. Is it so hard to understand that a computer operates on a giant array of bytes?

I think the hard thing to understand is that C’s pointer syntax is backwards (usage follows declaration is weird).

I also think understanding how arrays silently decay to pointers and how pointer arithmetic works in C is hard: ptr+1 is not address+1, but address+sizeof(*ptr)!

Pointers are not hard. C is just confusing, but happens to be the lingua franca for “high level” assembly.

> Is it so hard to understand that a computer operates on a giant array of bytes?

Beginner programming languages universally (since BASIC and Pascal) were designed to hide this fact. There's nothing in a beginning Python course that explains the true nature of computers. You learn about syntax, semantics, namespaces, data structures and libraries. But there's nothing that says, "a computer is endlessly incrementing a counter and executing what it finds where the counter points". And this is probably partly because of "go-to considered harmful", which posited that a lack of control flow (which is a fundamental fact of how computers actually work) is harmful to reasoning about programs.

It's probably objectively true. But a lack of go-to also restricts people from seeing the fundamental truth of the indistinguishable nature of data and instructions in the Von Neumann architecture. Which may also make it difficult to explain GPU computing to students (because it must be understood by contrasting it with Von Neumann architecture).

agreed! A fantasy CPU is good for the first project.

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