A vacuum pumping system comprising: at least one vacuum pumping mechanism; a motor for driving said at least one vacuum pumping mechanism; wherein said vacuum pump comprises means for determining a cumulative load on said vacuum pumping system over time by monitoring a characteristic of said motor over said time; wherein said characteristic is a power required by the motor to drive the vacuum pumping mechanism; and means for activating a maintenance activity on said system when a cumulative value of said characteristic exceeds a predetermined amount wherein said vacuum pumping system is for a processing system comprising a processing chamber in which wafers can be processed and a transfer chamber through which wafers can be transferred to the processing chamber for processing and transferred from the processing chamber after processing, said vacuum pumping system further comprising: a first said vacuum pumping mechanism driven by a first said motor for evacuating gas from the processing chamber; and a second said vacuum pumping mechanism driven by a second said motor for evacuating gas from the transfer chamber; wherein said determining means determines a cumulative load on said vacuum pumping system over time by monitoring said characteristic of said first motor or said second motor (34, 38), wherein during pump down the second vacuum pumping mechanism reduces the pressure in the transfer chamber from a first pressure at which wafers are introduced to the transfer chamber to a second pressure at which wafers are transferred from the transfer chamber to the processing chamber for processing; wherein said monitored characteristic of said second motor increases during each pump down and decreases when said second vacuum pumping mechanism is not reducing pressure in said transfer chamber; characterised in that said cumulative load is a number of wafers processed by the processing system and said determining means is configured to determine said cumulative load by counting a number of increases in said monitored characteristic of said second motor. at least one vacuum pumping mechanism; a motor for driving said at least one vacuum pumping mechanism; wherein said vacuum pump comprises means for determining a cumulative load on said vacuum pumping system over time by monitoring a characteristic of said motor over said time; wherein said characteristic is a power required by the motor to drive the vacuum pumping mechanism; and means for activating a maintenance activity on said system when a cumulative value of said characteristic exceeds a predetermined amount wherein said vacuum pumping system is for a processing system comprising a processing chamber in which wafers can be processed and a transfer chamber through which wafers can be transferred to the processing chamber for processing and transferred from the processing chamber after processing, said vacuum pumping system further comprising: a first said vacuum pumping mechanism driven by a first said motor for evacuating gas from the processing chamber; and a second said vacuum pumping mechanism driven by a second said motor for evacuating gas from the transfer chamber; wherein said determining means determines a cumulative load on said vacuum pumping system over time by monitoring said characteristic of said first motor or said second motor (34, 38), wherein during pump down the second vacuum pumping mechanism reduces the pressure in the transfer chamber from a first pressure at which wafers are introduced to the transfer chamber to a second pressure at which wafers are transferred from the transfer chamber to the processing chamber for processing; wherein said monitored characteristic of said second motor increases during each pump down and decreases when said second vacuum pumping mechanism is not reducing pressure in said transfer chamber; characterised in that said cumulative load is a number of wafers processed by the processing system and said determining means is configured to determine said cumulative load by counting a number of increases in said monitored characteristic of said second motor. a first said vacuum pumping mechanism driven by a first said motor for evacuating gas from the processing chamber; and a second said vacuum pumping mechanism driven by a second said motor for evacuating gas from the transfer chamber; wherein said determining means determines a cumulative load on said vacuum pumping system over time by monitoring said characteristic of said first motor or said second motor (34, 38), wherein during pump down the second vacuum pumping mechanism reduces the pressure in the transfer chamber from a first pressure at which wafers are introduced to the transfer chamber to a second pressure at which wafers are transferred from the transfer chamber to the processing chamber for processing; wherein said monitored characteristic of said second motor increases during each pump down and decreases when said second vacuum pumping mechanism is not reducing pressure in said transfer chamber; characterised in that said cumulative load is a number of wafers processed by the processing system and said determining means is configured to determine said cumulative load by counting a number of increases in said monitored characteristic of said second motor.