Hypervisor Removal

A computer comprises a plurality of operating systems 108-110, each including a GPU driver. The computer also has a graphics processing unit (GPU) 102 including GPU firmware and, for each operating system, a firmware state register modifiable by the GPU firmware and indicating whether the GPU firmware is online, and an OS state register modifiable by the GPU driver of the respective operating system and indicating whether the GPU driver is online. A memory management unit mediates access to the GPU registers such that each operating system can only access its own registers. The GPU has access to a timer and comprises a watchdog process 129 and, for each operating system, a firmware timer register and OS return register. The watchdog process periodically writes the timer value into the firmware timer register for each operating system, and each OS GPU driver periodically copies the time value from the firmware timer register into the OS return register. The watchdog process compares the time value of the OS return register to the firmware timer register to determine whether that operating system is online.