|The very short version...
In the beginning there was machine language very closely tied to the CPU. It worked with numeric opcodes that programmers has to literally memorize or look up. This got old real quick.
Enter assembly. It's not a compiler. It's an assembler and also a linker as part of a toolset. There's a difference. A compiler will translate code into something that's a one-to-one correlation with machine instructions. Assembly is already that. It's a language that basically gave human-memorable mnemonics to the opcodes. It was originally written in machine language. It's very CPU specific too. This too got old.
ML Pseudocode:Instruction Operation
00000000 Stop Program
00000001 Turn bulb fully on
00000010 Turn bulb fully off
00000100 Dim bulb by 10%
00001000 Brighten bulb by 10%
00010000 If bulb is fully on, skip over next instruction
00100000 If bulb is fully off, skip over next instruction
01000000 Go to start of program (address 0)
There were a ton of other languages made, presumably written in ASM, but this is where a compiler kicks in. To make a really long story short, I'll just mention C's history. C was based on B and B was based on BCPL. I don't know what BCPL was written in, but the first B compiler was written in BCPL. Eventually, the B compiler was re-written in B itself and then the first C compiler was written in that version of B.
A language written its own compiler happens more than you'd think. Anyway, these are still native compilers and eventually they still make their own down to machine code. Now, things like Java and C# I suspect are still written in native languages for obvious reasons, but don't be surprised if a native language's compiler is written in the same language.
This sounds great in theory, but if you look at how bloated and not-fun the Win32 API is, if you always have to maintain backwards compatibility then you keep things bloated when attempting to advance. I mean, it's good on one level, but it's also good to wipe out the old and try something new, like Apple is doing with the M1 chips (even though nothing is every really new, but you get the idea).
Calin Negru wrote:a standard should be required where the numbers/machine instructions for MOV are recognized everywhere. I mean it should work like a hardware resource with the same ID present on old and new processors.
Do we really want processors in 100 years having similar constraints as one designed in the 1960s? Rather than enforce that on the CPU, the industry has (correctly so) to rather have compiler targets implemented. You use your preferred language and it compiles down to whatever the CPU expects with optimizations, etc.