1. A method of processing data with one or more data processing threads executing under control of a first operating system upon a processor and one or more data processing threads executing under control of a second operating system upon said processor, said method comprising the steps of: executing a first data processing thread under control of said first operating system; triggered by said first data processing thread, generating a call with said first operating system to said second operating system to trigger execution of a second data processing thread operating under control of said second operating system; wherein said call passed from said first operating system to said second operating system includes an identifier enabling discrimination by said second operating system between calls triggered by different data processing threads executing under control of said first operating system.