IBM uses the same mechanism as many major microprocessors, deeply merging the register file with the decoder but its register file are work independently by the decoder side and do not involve context switch, which is different from Alpha and x86. most of its register file not just serve for its dedicate decoder only but up to the thread level. For example, POWER8 has up to 8 instruction decoders, but up to 32 register files of 32 general purpose registers each (4 read and 4 write port), to facilitate simultaneous multithreading, which its instruction cannot be used cross any other register file (lack of context switch.).