The world of CPUs is a dark, deadly, and dangerous place. After all, the CPU is said to be the literal “heart” of the PC – and as such, it’s the single most-heavily engineered component. Billions of dollars and manhours have gone into the design of these various chipsets and they’ve all been researched, optimized, fabricated, and sold in order to make your computer… better.
The biggest difference between these platforms is the design dogma they follow. The x86 is a CISC architecture: Complex Instruction Set Computer. The ARM is a RISC-based designs: Reduced Instruction Set Computer.
CISC architectures can have up to thousands of individual commands supported by the processor that can be used in machine code. Each of these assembly commands can range from a single operation to several hundred or more in length. On the other hand, RISC-based CPUs understand only a handful of different instructions, the minimum necessary to get the job done.
However, this in no way means that CISC is more powerful or that RISC is limited. The difference between the ARM and Intel can be explained with booting process of an OS.
In the Intel x86 architecture the bootloader is called from BIOS (Basic Input / output system). It then loads the kernel into RAM from the filesystem, & execute the kernel. At this point the kernel has control & accesses the filesystem. On an Intel architecture you need only to place the bootloader on the boot sector of the hard drive and have an accessible filesystem.
On the ARM, there is no BIOS, & no delay for the POST. There is also no hard drive. So the first thing to run is the bootloader, which then loads the kernel directly from flash (and not of a filesystem). The bootloader passes execution to the kernel. The kernel then accesses the filesystem & things are pretty similar to an x86 boot sequence from there.
The other important difference between the Intel world & the ARM world is that the bootloader is also used to transfer the OS image onto the flash device