Fundamentally, what is a PC architecture, what is the difference between x64, x86, ARM, whatever else etc. and why do they offer different benefits or drawbacks or performances
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A *CPU* architecture is how the CPU is designed, what kind of instructions it accepts, how much internal memory it has, etc.
There’s architecture and microarchitecture – different microarchitectures work differently internally but still run the same programs (hopefully faster) – different architectures can’t run the same programs and need different versions of programs.
x64 is the 64-bit upgrade to x86 – a new architecture, but since it’s meant to be an upgrade, x64 CPUs also know how to run x86 programs. ARM is something different entirely, traditionally used for battery-powered things because it has better power efficiency, but in the last few years it’s also getting a lot more use in servers.
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The obvious difference between different architectures is they run different program instructions. Because of x86/x64’s history the instructions are quite complicated, while ARM’s are quite simple. That means in ARM you need more of them to make a program, and each instruction takes up more memory than equivalent x86/x64 one, but on the other hand, there aren’t a bunch of transistors devoted to making sense of the complicated instructions, and if they are locked into making every instruction use the same amount of memory.
Since the ARM designers didn’t focus on making instructions small, they also had some leftover bits in each instruction, which they used for purposes not found in x86, which did focus on that. On the 32-bit version of ARM, every instruction is also an if-then statement – for free – and there are more registers (temporary holding locations for numbers).
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