Kdb+ operating system version as a symbol.

q).z.o
`w32

Values for V3.5+ are shown below in bold type.

os 32-bit 64-bit
Linux l32 l64
macOS m32 m64
Solaris s32 s64
Solaris on Intel v32 v64
Windows w32 w64

Note this is the version of the kdb+ executable, NOT the OS itself. You might run both 32-bit and 64-bit versions of kdb+ on the same machine to support older external interfaces.