The Unabridged Pentium 4 IA32 Processor Genealogy

Entering or Reentering VM86 Mode

Task Creation, Startup and Suspension

Create a TSS

Before the multitasking OS initially starts a DOS task, it creates a 32-bit TSS for the task, setting the EFlags[VM] bit to one in the TSS's EFlags field. It also creates a TSS descriptor (in the GDT) that points to the task's TSS in memory.

Each Task Gets a Timeslice

A multitasking OS usually permits a task to execute for a predefined period of time, typically referred to as a timeslice. This is accomplished by triggering a hardware timer prior to starting (or resuming) the task. The task is then started by the OS scheduler and continues to execute until a hardware interrupt is generated by the timeslice timer (unless the task is interrupted prior to this for ...