TABLE 9-1   WINDOWS SOFTWARE INTERRUPTS
Interrupt Number	Functionality
2Ah	Used to get the current timer tick count.
2Bh, 2Ch	Used by the CSRSS subsystem to force an immediate thread switch. This occurs as part of a LPC mechanism. We discussed LPC in more detail in Chapter 8. These interrupts are used only in Windows NT 3.51 since in later versions of Windows NT, most of the functionality in CSRSS is moved to a kernel-mode driver WIN32K.SYS.
2Dh	Debugging service. This service, used by driver writers, outputs debugging messages to the Debugger Window. The DbgPrint() function provided in DDK calls this interrupt to output debug messages.
2Eh	This interrupt is extensively used for calling system services provided by Windows NT. The system services are provided by two components viz. NTOSKRNL and WIN32K.SYS. The services provided by WIN32K.SYS are present only in Windows NT versions later than 3.51. We discuss system services in detail in Chapters 6 and 7.