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Comment by cabaalis | Hacker News Reader

>Also, it's interpreters all the way down. Even assembly is interpreted.

Speak truth to power. Every time someone says this there seem to be nothing but haters.

> Every time someone says this there seem to be nothing but haters.

Because it's not completely true. If a CPU is microcoded, then it's accurate to say "assembly is interpreted" because every instruction is effectively an address into a lookup table of microinstructions. But in a non-microcoded (e.g. purely RISC) CPU, the bits of the instruction word are effectively enable and data lines to a bunch of hardware logic gates and flip-flops, which cause register transfers and arithmetic operations to happen. In this case, the ones and zeros in the instruction word are voltage levels on logic gates. Calling the latter "interpretation" is a stretch.

To be fair, there aren't many pure RISC implementations around these days. Most everything has some degree of microcode involved, so to that extent you're right.

It's interpreted because the instructions are fetched one by one. A piano roll is intepreted, even though its holes just activate keys with a "horizontal encoding". It is interpreted because it moves through the piano, and a little piece of it activates a behavior any one time, without leaving a permanent record.

Not only is machine code interpreted, the so-called "asynchronous interrupts" are just periodically polled for in between the fetching, decoding and executing.

>Even assembly is interpreted.

Could you please elaborate on this point? I'm still very much in the cave.

I'll use x86-32 for elaboration [1]. When the CPU sees the byte sequence 0xB8 0x90 0x41 0x5A 0x7B, it has to interpet what those bytes mean. It sees the 0xB8, so then it knows that you are loading the EAX register with an immedate value. The next four bytes (0x90, 0x41, 0x5A, 0x7B) are read and stored into EAX (as 0x7B5A4190, because Intel is little endian).

That is the case for all instructions. Each one is interpreted by the CPU. And for modern CPUs, even translated into an internal format that is futher interpreted.

[1] Sans power right now. Using my cellphone as a hot-spot and my iPad as a laptop. The aftermath of hurricanes is brutal in Florida.

Gotcha, but then (unless I'm misunderstanding) one of these interpreters is not like the other. Namely, assembly 'interpretation' happens on bare metal. Were you previously suggesting that understanding a lisp interpreter will help in understanding CPU architecture?

(Good luck recovering from the hurricane! Keep your head down!)

I was replying more to jospar's post about learning what an 'if' was, what a 'boolean' was, etc. What's an 'if'? Ultimately it's a comparison of two numbers and a transfer of control based upon said comparison. Some architectures that's one instruction, some two.

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