66 lines
2.3 KiB
Markdown
66 lines
2.3 KiB
Markdown
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---
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tags: [CPU]
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---
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# Instruction Set Architectures
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## Summary
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- Computers with different hardware execute machine code instructions (e.g
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_add_) in different ways. They have different _instruction set architectures_
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(ISAs).
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- A family of CPUs that implement the core instructions of the
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[[Arithmetic_Logic_Unit]] in the same way share an ISA. Any software built for
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that ISA will work on any CPU that implements the ISA
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- The two main CPU architectures are ARM and x86
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## Architecture is logical not physical
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The "architecture" of an ISA is logical rather than physical, i.e processors
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that share an ISA may work very differently on the hardware level whilst still
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adhering to the same instruction set.
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## ARM and x86
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The two main processor architectures are ARM and x86. x86 processors were first
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introduced by Intel but are also made by AMD.
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### x86
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- First introduced by Intel but also made by AMD.
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- Name stems from Intel's internal naming conventions - every new processor they
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introduced would have a letter designation ending with "86". Later they would
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adopt names such as "Pentium", "Celeron" etc. Regardless, these processors
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still fall under the "x86" family.
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- Over time, new instructions have been added to the x86 architecture but they
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all maintain backwards compatibility with preceding generations.
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- There have been different, successive generations of x86 corresponding to
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their [word-size](Signed_and_unsigned_numbers.md): 16-bit, 32-bit, 64-bit.
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Word size here just means how many bits the processor can work with at a time.
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A 34-bit processor can operate on values that are 32 bits in length. This
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means it has 32bit [[CPU_architecture#registers|registers]], a 32-bit data
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[[Bus|bus]], a 32-bit address bus and so on.
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- AMD introduced the first 64-bit processor, not Intel but they later caught up.
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A 64-bit x86 processor is often referred to as _x64_ or _x86-64_.
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### ARM
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- x86 processors dominate the personal computer and server space
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- On movile devices ARM ISA predominates
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- The ARM company develops the architecture and standard which it licenses it to
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other companies to implement.
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- Preferred on mobile because they have reduced power consumption and lower
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costs compared to x86.
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- The processor is on a single chip that contains the CPU as well as memory and
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other hardware.
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