Support FAQs for Continuum products

Why do I need special software to keep accurate time? Isn't the clock in my computer accurate enough?

How do the hardware and software clocks work together?

Doesn't my hardware clock use a crystal to keep accurate time?

Is Continuum Y2K compliant?

How long will this protocol work?

Why do I need special software to keep accurate time? Isn't the clock in my computer accurate enough?

Since the introduction of the IBM PC AT in 1984 all PC-compatible computers have kept time in the same way using two clocks, one in software and one in hardware. The software clock is generated by an Intel 8254 timer-counter (or equivalent device) which generates an interrupt every 54.936 ms, about 18.2 times per second. The BIOS (Basic Input/Output System) contains a software routine that counts the interrupt requests and generates a time-of-day clock that can be used by other programs, but this software clock is a very poor time keeper. Its uncertainty is exacerbated by the instability of the interrupt requests. Any change in the interrupt rate causes the clock to gain or lose time. If a computer is left on for long periods of time the software clock might be off by perhaps a minute or more for every day the computer has been on.

How do the hardware and software clocks work together?

When the computer is turned off the software clock stops running and loses all of its time-of-day information. For this reason the hardware clock is necessary. The hardware clock is based on the Motorola 146818 real time clock chip, or an equivalent device. When the computer is off the hardware clock runs off a battery. When the computer is turned back on the software clock starts running again and sets itself to the hardware clock (within one second).

Doesn't my hardware clock use a crystal to keep accurate time?

Yes, but the hardware clock is updated only once per second and cannot display fractions of a second. Its timing certainty is limited by the quality of the crystal oscillator it uses. These crystals offer only marginal timekeeping performance. They are sensitive to temperature and other factors and their frequency certainty is not likely to be better than 1x10-5 (or about 1 sec/day). In actual operation most hardware clocks gain or lose about 5 to 15 seconds/day. (Derived from the Internet article Computer Time Synchronization, Michael Lombardi, Time and Frequency Division, NIST)

Is Continuum Y2K compliant?

Umm, have you looked at your calendar recently?

If you haven't, then the answer is "yes it is compliant". Continuum products use the Time Protocol (RFC-868) to send and receive times. This simple protocol uses a 32-bit unformatted binary number to represent time in UCT (Universal Coordinate Time) seconds since January 1, 1900.

How long will this protocol work?

The maximum number that can be represented with 32 bits is 4,294,967,295. This corresponds to a little over 136 years, which means that Continuum products in their current form will operate smoothly until around early February of 2036. At the moment there is no provision for increasing either the resolution (1 second) or range of years (~136) of this time protocol.