> Unrelated: why do they call the instruction set an architecture or ISA? In the early days of all of mainframes, minicomputers, and microprocessors companies

> Unrelated: why do they call the instruction set an architecture or ISA? In the early days of all of mainframes, minicomputers, and microprocessors companies slapped some hardware design together and then made un an instruction set for it. When the same company made a better, faster, shinier computer a few years later the hardware was completely different and the instruction set was completely different and everyone had to rewrite their software. One of the best-known examples is the Intel 4004, 8008, 8080, 8086 and so on. None of them can run software for either later or earlier chips. Intel was reasonably good at making it not too hard to rewrite old software, but it still had to be done. An Instruction Set ARCHITECTURE is an instruction set that is designed from the outset to be independent of any particular hardware implementation of it, and it is intended to make and sell machines over a long period of time that can all run the same software. Not only that, but with, for example, the IBM System/360 introduced in 1964 they announced six different machines (Models 30, 40, 50, 60, 62, and 70) on the same day, with about a 20:1 "commercial" performance ratio (90:1 for "scientific" use) and a similar range of monthly rental costs (IBM didn't sell them outright). RISC-V is similarly deliberately an Instruction Set Architecture, that works well with a very wide range of implementation techniques and cost/size, all of which can run exactly the same software (at least if it sticks to RV32I / RV64I).