Memory Mode of a Process

Prior to INtime 6, non-XM mode was used; here a process has a memory space that may have non-zero-based segment registers. These register values can affect performance on Intel Atom processors, so XM mode is recommended.

Every XM mode process has a complete 4GB virtual address space (minus a 256 MB space to map system code and data), which uses zero-based segment register values.

Using XM mode is the default in INtime 6. However, XM mode processes and legacy processes can be mixed.

The individual virtual address space of XM mode processes results in switches between address spaces in the following situations:

Every system call (the system has its own address space)
Thread switches between threads in a XM process and other processes
Handling interrupts when a XM process is running

The overhead in each case is very small.