An FPGA is not like a cpu microprocessor that is a premade circuit if you like and can only function one way when it was designed, eg: a intel/amd cpu or commodore 6502 / motorola 68000 with pins underneath etc. An FPGA comes in the shape of a cpu if you like, but think of it as a place where you can store other chips inside of it for one thing a CPU. eg: Imagine if your intel CPU was pulled apart and then remade into Software again and then loaded into inside the FPGA chip. This not only has the benefit of being able to store the CPU in software inside it, but also has the added benefit of being able to change that intel CPU in anyway desired to be like the original or any other way desired. not only could a cpu be stored inside an FPGA, but you might also store an FPU (Floating point unit) and MMU (memory management unit) inside it, along with maybe computer roms etc. FPGA’s are very large these days which makes them far more flexible space savers for one thing, but much simpler for a programmer to change in the future not being stuck with a premade cpu anymore. These can be changed when required, without the huge cost to make new cpus for example all the time.
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