Register file
Beginner
The tiny, fastest memory right next to the math units, where each worker keeps the numbers it’s using right now.
Novice
The bank of registers inside a processor core. On a GPU it is huge (hundreds of kilobytes per core) because every resident thread keeps its own registers there all the time.
Expert
65,536 32-bit registers (256 KB) per NVIDIA SM since Kepler-era designs; 256–512 KiB of VGPRs per AMD CU. It’s partitioned among resident warps, so registers per thread trade directly against occupancy.