1. A method for emulation of a target system on a host system, the method comprising: determining statistics for use of a set of registers of a target system processor; based on the statistics, determining a first subset of registers of the set of registers, the first subset including one or more most commonly used registers; directly mapping the first subset of registers to a first group of registers of a host system processor; dynamically mapping a second subset of the set of registers to a second group of registers of the host system processor; and emulating the target system processor on the host system processor using the first and second groups of registers wherein some of the registers in the set of registers of the target system processor are larger than the registers in the first and second groups of registers of the host system processor; and wherein directly mapping the first subset of registers or dynamically mapping the second subset of registers includes mapping a lower field of a target system register to a first host system register and mapping an upper field of the target system register to a second host system register.