Abstraction is essential
We combine technological primitives to design more complex components, repeating this process over and over to scale up larger and larger systems.
Combine transistors into logic gates, logic gates into Boolean functions, Boolean functions into modules, modules into a processor core, processor cores into a multiprocessor, and we end up with a CPU.
Instruction set architecture (ISA)
Computers read and perform instructions in their own specific language, usually bytecode (which is either interpreted or further compiled down) or machine code.
All high-level languages are compiled down to an even more rudimentary language that only computers can interpret.
It’s not that humans can’t read machine code. It’s just that programming C is much easier than reading… binary, and C is considered one of the more low-level languages out there.
There are many types of computers that run different instruction sets. This includes x86, ARM, RISC-V, PTX, SPARC, and LC-4 (Penn’s imaginary ISA).
The ISA specifies the hardware’s interface, permitting us to write and run software on the processor. It defines the set of instructions implemented by the processor, the number of storage locations, and the Data types it supports.
If we think of a computer in layers, the ISA is the interface layer between hardware and software.
However, it doesn’t “physically” exist.
Microarchitecture
ISAs don’t “physically” exist. Instead, it’s implemented by a microarchitecture, which actually brings it to life. Microarchitectures define how the computer hardware is actually designed, organized, and built.
There are many different microarchitectures that conform to the same ISA, and there are many ways to build hardware that provide the same interface to software.
Computer architects rarely mess with the ISA. However, microarchitectures are often created for many different reasons.
- Accelerate new applications and tech (AI, quantum, new transistors, etc.)
- Optimize and balance designs (best for power, or efficiency, or security, etc.)
Example
The original x86 ISA was implemented by Intel’s 8086 chip in 1979.