[brucehoult]

The publication of the initial 1.0 frozen ISA spec was in mid 2019, five years ago. That was enough stuff for embedded devices, including basic Linux support.

A ton of instructions needed for more serious things -- vectors, hypervisor, crypto, cache control operations, more -- were published in December 2021, 2 1/2 years ago. The first chips with that spec (called RVA22) have been hitting the market in the last few months. An early Core i7 level chip with RVA22 will come out late this year, a Pentium III level (but 8 core) one is out now in the BPI-F3 and soon Milk-V Jupiter (MiniITX board).

A lot more almost as important instructions have been published since then. The RVA23 spec is about to be ratified in the next few months. That will be the likely LTS baseline for Android and other mobile and desktop OSes that you will see around 2026 or 2027, just as (hopefully) desktop-class (at least similar to Snapdragon X Elite) chips come out.

How long has RISC-V been around? Very little time. As of right now, it's four years behind Arm, with the gap closing.