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Top Forums UNIX for Advanced & Expert Users The UNIX clock/timer interrupt Post 302958810 by Ultrix on Monday 26th of October 2015 02:50:33 PM
Old 10-26-2015
The UNIX clock/timer interrupt

The book The Design of the Unix Operating System speaks of a clock or timer that is used in scheduling. The clock generates interrupts that update priority information for processes and preempt processes in a round-robin fashion. It's apparent that this "clock" is not the same thing as the CPU clock, since is only generates 50 to 100 signals every second, as opposed to millions or billions of pulses a second. It's also apparent that it's not the same thing as the mechanism that keeps track of the date - that is to say, the number of seconds since midnight before January 1, 1970. So what exactly is it? Is it a pulse generator? Does it store a value that increments? Is it synced with the CPU clock somehow? How does it work? And how can it be "reset"?
 

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CLOCK(1)						      General Commands Manual							  CLOCK(1)

NAME
clock - display the time in an icon or window SYNOPSIS
clock AVAILABILITY
This command is available with the OpenWindows environment. For information about installing OpenWindows, refer to the OpenWindows Instal- lation and Start-Up Guide. DESCRIPTION
clock is an OpenWindows XView utility that displays the current time in a window or icon. When the window is open, clock can display the time in either analog or digital format. The clock window is scalable in either format. USAGE
When the clock window is open, it has a floating menu from which you can bring up a property window. From this property sheet, you can modify the display of the tool by selecting either the Analog or Digital choice box. Seconds: On the analog version, this selection starts a second hand on the face of the clock. On the digital version, it adds two dig- its to the digital readout. Date: Turns on a date display for both analog and digital versions of clock. BUGS
If you reset the system time, clock will not reflect the new time until you change its window state from open to icon, or vice versa. To reset the system time, see date (1V). The date display does not go well with the round clock face. Occasionally, when clock is uncovered, the face will be visually corrupted. Use the Refresh button from the frame menu to repair. 11 June 1990 CLOCK(1)
All times are GMT -4. The time now is 11:22 PM.
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