
Nibbler 4 Bit CPU - kephra
http://www.bigmessowires.com/nibbler/
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richdougherty
_Nibbler also lacks any address registers, which means it can’t support any
form of indirect addressing, nor a hardware-controlled stack. All memory
references must use absolute addresses._

Wow!

~~~
PythonicAlpha
Yes, it is a very limited design, but the thought, that it was implemented
just using (very few!) standard 74xxx TTL logic is really amazing.

And still it runs with 1MHz, the same speed of my first computer ;) with a
dedicated integrated CPU.

~~~
makomk
It's implemented using a few standard 74xxx TTL logic chips and a 256x16
microcode ROM. It's important not to ignore the microcode ROM because that's
where all the smarts that turn it from an ALU unit and a bunch of registers
and miscellaneous logic into a CPU that can actually execute instructions. All
of the instruction decoding and the sequencing of all the operations that make
up a CPU cycle is done directly by the microcode ROM.

~~~
creshal
Two 16 KiB ROMs, actually.

(Meanwhile, current Intel processors have 2 MiB microcode files.)

~~~
k8tte
to be fair, that's 2 MiB code that is the base of the other os you never heard
of, the IME, AMT and their backdoor capabilities [1]

1: [https://fsf.org/blogs/community/active-management-
technology](https://fsf.org/blogs/community/active-management-technology)

~~~
creshal
No, that's just the CPU µcode. IME/AMT are part of the BIOS/EFI images, which
is a whopping 16 MiB for my current motherboard.

~~~
makomk
The current CPU microcode download appears to be 0.81 MB compressed for every
single Intel CPU since the Pentium 4.

