What is a Register File?

The register file is the fastest layer of on-chip memory inside a Streaming Multiprocessor, the place where values actually sit while the GPU cores read and write them between instructions. It runs roughly an order of magnitude faster than the SM's own L1 cache, the same relationship a CPU's registers have to its L1.

Physically, it's a bank of 32-bit registers that gets carved up on demand: a thread can claim one register as a 32-bit integer, pair two together for a 64-bit float, or pack several as smaller 16-bit values. Those physical registers are what back the virtual registers that PTX, CUDA's intermediate representation, assigns to each warp of threads.

A compiler decides at build time how many physical registers each thread in a thread block actually gets. Ask for too many per thread, a state known as high register pressure, and fewer threads fit in the register file at once, which lowers occupancy and leaves the SM with less other work on hand to hide memory latency behind. Register file size varies by GPU generation, one more spec worth checking on the Aquanode GPU pages before assuming a kernel tuned for one architecture will occupy the same fraction of the next.

register file

The register file is the fastest layer of on-chip memory inside a Streaming Multiprocessor, a bank of 32-bit registers where values sit between instructions. The compiler decides at build time how many registers each thread gets. Asking for too many per thread lowers occupancy, because fewer threads fit in the register file at once.

Register file size depends on the architecture and compute capability, both listed in the L40 vs RTX A4500 specs and the RTX 4000 Ada vs RTX 5080 specs. Browse the full lists: All GPU glossary terms explained and Compare any two GPUs side by side.