What Does the Zw Prefix Mean?

The Windows native system services routines have names that begin with the prefixes Nt and Zw. The Nt prefix is an abbreviation of Windows NT, but the Zw prefix has no meaning. Zw was selected partly to avoid potential naming conflicts with other APIs, and partly to avoid using any potentially useful two-letter prefixes that might be needed in the future.

Many of the Windows driver support routines have names that begin with two- or three-letter prefixes. These prefixes indicate which kernel-mode system components implement the routines. The following table contains some examples.

Prefix	Kernel component	Example routine
Cm	Configuration manager	CmRegisterCallbackEx
Ex	Executive	ExAllocatePool
Hal	Hardware abstraction layer	HalGetAdapter
Io	I/O manager	IoAllocateIrp
Ke	Kernel core	KeSetEvent
Mm	Memory manager	MmUnlockPages
Ob	Object manager	ObReferenceObject
Po	Power manager	PoSetPowerState
Tm	Transaction manager	TmCommitTransaction
Nt and Zw	Native system services	NtCreateFile and ZwCreateFile