Where can data be stored? - Address space
Several address spaces are distinguished by the (assembly language) programmer, such as register space, stack space, heap space, text space, I/O space, and control space.
Except for the registers, all other address spaces are mapped onto a single contiguous memory address space.
A RISC ISA additionally contains a register file, which consists of a relatively large number of general-purpose CPU registers- early RISC processors: MIPS: 32 32-bit general purpose registers,RISC I: register windowing
Contemporary RISC processors: additionally 32 64-bit floating-point and multimedia registers.