Three types of SMUs are available: 

HRSMU (high resolution SMU) 

Force and measure: up to ±100 V or ±100 mA. 

Maximum output power: 2 W. 

Minimum current measurement range: 10 pA with 1 fA resolution. 

Only the 4156B has HRSMUs. The 4156B has four HRSMUs. 

MPSMU (medium power SMU) 

Force and measure: up to ±100 V or ±100 mA. 

Maximum output power: 2 W. 

The 4155B has four MPSMUs, and the 41501A/B can be equipped with either two MPSMUs or one HPSMU. 

HPSMU (high power SMU) 

Force and measure: up to ±200 V or ±1 A. 

Maximum output power: 20 W. 

Only the 41501A/B has HPSMU. The 41501A/B can be equipped with either two MPSMUs or one HPSMU.