TF: It is used for single-step control. It allows user to execute one instruction of a program at a time for debugging. When TF is set to 1, a program can be run in single-step mode. When an interrupt is recognized, the TF flag is automatically cleared. When the CPU returns back to the main program after executing interrupt service subroutine, the TF flag is restored to the state in which it was before the interrupt occurred. This is achieved by executing IRET instruction at the end of the interrupt service subroutine. There is no instruction to set or reset TF flag directly. So its setting or resetting can be done by pushing the flag register on the stack, taking necessary steps to change the TF bit as desired and then popping the flag register back off the stack.

VM: Used to switch to virtual 8086 emulation. Used in Intel 80x86.