6502	8-bit architecture	3 User registers Mixed purpose A - 8-bit accumulator x - 8-bit index y - 8-bit index Stack Pointer - 8-bit. Fixed location. 16-bit Instruction Pointer
80x8	16/32/64-bit architecture	4 Mixed purpose regsiters A - Accumulator B - Base register C - Counter register D - suplimentary (math) 4 Pointer registers SP - 16 bit stack pointer. Relocatable BP - 16 bit base pointer secondary access to stack SI - 16 bit source index DI - 16 bit destination index IP - 16-bit instruction pointer 4 Segment registers SS - Stack segment used with BP and SP CS - Code segment used with IP DS - Data segment used with SI ES - Extra segment used with DI
IBM 360	32/64-bit architecture	16 GPR registers R0 - Null when uses as addess pointer 4 Floating point registers PSW - program status word Contains : Condition codes Instruction pointer Supervisor/Task flag Various I/O masks
Z8	8/16 bit architecture		Register file cotains between 128-4K registers.