June 3rd, 2009

What does the “Zw” prefix mean?

Raymond Chen
Raymond Chen

If you spend time in kernel mode, you’re accustomed to seeing functions with two-letter (or occasionally, three-letter) prefixes that indicate which component they belong to.

Prefix Component Example
Ex Executive ExAllocatePool
Hal Hardware abstraction layer HalGetBusData
Io I/O manager IoAllocateIrp
Ke Kernel KeBugCheck
Ks Kernel streaming KsAcquireControl
Mm Memory manager MmGetPhysicalAddress
Ob Object manager ObReferenceObjectByHandle
Po Power management PoSetSystemState
Se Security SeAccessCheck
Tdi Transport driver interface TdiProviderReady
Zw ???? ZwCancelTimer

What does the “Zw” mean?

Answer: Nothing.

The people who chose the letters wanted to pick something that was unlikely to collide with anything. Perhaps they had a prior bad experience with having chosen a prefix, only to find that somebody ahead of them claimed it already?

Category
Old New Thing
Topics
History

Author

Raymond Chen

Raymond has been involved in the evolution of Windows for more than 30 years. In 2003, he began a Web site known as The Old New Thing which has grown in popularity far beyond his wildest imagination, a development which still gives him the heebie-jeebies. The Web site spawned a book, coincidentally also titled The Old New Thing (Addison Wesley 2007). He occasionally appears on the Windows Dev Docs Twitter account to tell stories which convey no useful information.

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