How do you know if a user is idle?

[Earl Locken]

How does the system tell if a user is idle?  We run SunOS here, and
where does the "w" command get the info it prints as the idle time?

Thanks.

Earl Locken
Alberta Microelectronic Centre
#200, 1620-29 St. NW, Calgary, Alberta, Canada  T2N 4L7
UUCP: ...{alberta,ubc-cs,utai}!calgary!amc-vlsi!earl