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if The ISA acts as an interface between the hardware and the software why we have firmware? What exactly is firmware and how it works.

panos
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  • The ISA is a specification that both processor hardware and software application programs adhere to. Firmware is another ISA that would generally be wholly internal to a device; firmware allows devices to be composed of an internal processor with internal software. There's no reason for the firmware of a device hidden internally to use the same instruction set architecture as the main system processor. – Erik Eidt Mar 21 '22 at 19:48

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You're comparing apples and oranges here; or perhaps, apples and cider...

An ISA, by which I presume you mean Instruction Set Architecture, is a definition of what a processor does. It's a list of promises, like "if you send this instruction, this register will be copied to this other register".

Firmware, on the other hand, is software to define how a component does something. It's software that says things like "if input is equal to this, then run this sequence of steps". Firmware allows the same arrangement of hardware to implement different tasks, or for problems to be fixed without having to build an entirely new chip.

In the case of modern CPUs, there is a type of firmware called microcode which is used to implement the ISA by taking the inputs the ISA specifies, and defining the lower-level steps that need to be carried out on the actual hardware.

IMSoP
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