Hacker News Reader

Comment by timmisiak | Hacker News Reader

I think both are useful, but designing a modern CPU from the gate level is out of reach for most folks, and I think there's a big gap between the sorts of CPUs we designed in college and the sort that run real code. I think creating an emulator of a modern CPU is a somewhat more accessible challenge, while still being very educational even if you only get something partially working.

View on HN

When I was at Caltech, another student in the dorm had been admitted because he'd designed and implemented a CPU using only 7400 TTL.

Woz wasn't the only supersmart young computer guy at the time :-)

(I don't know how capable it was, even a 4 bit CPU would be quite a challenge with TTL.)

I think the key word above was modern. I felt able to design a simple CPU when I finished my Computer Architecture course in university. I think I forgot most of it by now ;) There are a few basic concepts to wrap your head around but once you have them a simple CPU is doable. Doing this with TTL or other off the shelf components is mostly minimizing/adapting/optimizing to those components (or using a lot of chips ;) ). I have never looked at discrete component CPU designs, I imagine ROM and RAM chips play a dominant part (e.g. you don't just built RAM with 74x TTL flip-flops).

He probably used off-the-shelf RAM chips, after all, RAM is not part of the CPU.

In the early 70s, before the internet, even finding the information needed would be a fair amount of work.

I learned how flip flops worked, adders, and registers in college, and that could be extended to an ALU. But still, that was in college, not high school.

I've read some books on computer history, and they are frustratingly vague about how the machines actually worked. I suspect the authors didn't actually know. Sort of the like the books on the history of Apple that gush over Woz's floppy disk interface, but no details.

Was doing some Googling and came across: https://en.wikipedia.org/wiki/Breakout_(video_game)

I never heard this story...

> and the sort that run real code

And the sort that are commercially viable in today's marketplace. The nature of the code has nothing to do with it. The types of machines we play around with today surpass the machines we used to land men on the moon. What's not "real code" about that?

This is an illusion and a red herring. RTL synthesis is the typical functional prototype stage reached which is generally sufficient for FPGA work. To burn an ASIC as part of an educational consortium run is doable, but it's uncommon.

Reply on news.ycombinator.com