5 ms·

Reverse-engineering the flag circuits in the 8085 processor

64 points by kogir 13y ago

kogir 13y ago
I find stuff like this fascinating and marvel at how it's even possible to do via visual inspection alone. It's also sobering to think about how long it would take using a similar process to understand a modern, 20 nanometer chip.
- fein 13y ago
  I always look at things like this and say that I wish I understood every step of the process, from electrical theory to fabrication. I have the same approach to software, but I have to keep reminding myself that the things I'm trying to understand took hundreds of people to complete. It's an incredibly annoying internal struggle. I have no idea how to deal with it aside from grinding it all out until I die.
  - kens 13y ago
    Author here: I don't understand every step of the process either :-) But old chips like this at least seem theoretically possible to comprehend in their entirety. I expect it would be pretty much impossible to reverse-engineer and understand a present-day processor with billions of transistors instead of thousands. But I could be surprised - 35 years from now people may be reverse-engineering Xeon chips for fun. And perhaps posting about interesting things they found in Intel's random number circuitry.
kostyakow 13y ago
Thank you for this this great article! I am currently trying to learn more about the hardware and lower-level aspects of computer, and this was a really interesting read. You may be interested in checking out an emulator for original IBM computer my friend wrote: https://github.com/Alegend45/IBM5150 https://github.com/Alegend45/IBM5150 It's in really early stages of development, and the BIOS barely boots. Nevertheless, I enjoy reading the code and trying to understand how it works. I am trying to help him out with it, but I know very little about this kind of stuff (I am just starting out learning about hardware), so I haven't been of much help. Since you are knowledgeable in this subject area you can help him hack on it if you're interested!

64 points by kogir 13y ago

kogir 13y ago

I find stuff like this fascinating and marvel at how it's even possible to do via visual inspection alone. It's also sobering to think about how long it would take using a similar process to understand a modern, 20 nanometer chip.

fein 13y ago
I always look at things like this and say that I wish I understood every step of the process, from electrical theory to fabrication. I have the same approach to software, but I have to keep reminding myself that the things I'm trying to understand took hundreds of people to complete. It's an incredibly annoying internal struggle. I have no idea how to deal with it aside from grinding it all out until I die.
- kens 13y ago
  Author here: I don't understand every step of the process either :-) But old chips like this at least seem theoretically possible to comprehend in their entirety. I expect it would be pretty much impossible to reverse-engineer and understand a present-day processor with billions of transistors instead of thousands. But I could be surprised - 35 years from now people may be reverse-engineering Xeon chips for fun. And perhaps posting about interesting things they found in Intel's random number circuitry.

kostyakow 13y ago

Thank you for this this great article! I am currently trying to learn more about the hardware and lower-level aspects of computer, and this was a really interesting read. You may be interested in checking out an emulator for original IBM computer my friend wrote: https://github.com/Alegend45/IBM5150 https://github.com/Alegend45/IBM5150 It's in really early stages of development, and the BIOS barely boots. Nevertheless, I enjoy reading the code and trying to understand how it works. I am trying to help him out with it, but I know very little about this kind of stuff (I am just starting out learning about hardware), so I haven't been of much help. Since you are knowledgeable in this subject area you can help him hack on it if you're interested!