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Let's say you have a PC which is not connected to a time server, so it has no external methods of keeping track of time. You turn the machine on, and set the time and date in the BIOS.

Then you overclock said PC. Will the time run faster than usual because of the faster CPU cycles?

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If the CPU was the time keeping device, powering off your PC would also screw up the system time. – Pablo Marambio Oct 11 '12 at 22:52
up vote 37 down vote accepted

The system time is not based on the CPU but rather another chip on the motherboard, so overclocking the CPU will not alter the "speed" of the system time.

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Small correction: time is actually "kept" by a crystal oscillator. – Indrek Oct 11 '12 at 19:27

Nope. The clock is kept by the CMOS, and is not effected by the CPU overclock.

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Are you able to expand a little bit about what the CMOS does? – Canadian Luke Oct 11 '12 at 18:06
@Luke Check out (Wikipedia redirect for CMOS WRT PC BIOSes) – Mark Allen Oct 11 '12 at 18:22
Not for me, for the site. We're supposed to be a site of professionals, and a one-liner answer is usually discouraged – Canadian Luke Oct 11 '12 at 19:33

The clock speed of the CPU isn't based on the RTC, so you shouldn't see a change.

Note that clock drift happens on computers even at normal clockspeeds anyway, because the RTC isn't perfect to begin with. Clock drift is normal and expected (although it shouldn't be significant on normal systems).

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Timekeeping Basics

Computer operating systems typically measure the passage of time in one of two ways:

• Tick counting – The operating system sets up a hardware device to interrupt periodically at a known rate, such as 100 times per second.[...]

• Tickless timekeeping – A hardware device keeps a count of the number of time units that have passed since the system booted, and the operating system simply reads the counter when needed.[...]

[...] to correct for long-term drift and other errors in the measurement, the operating system [...] periodically checks the clock against a network time server [...]

Anecdote: we once had a 486 class server clock which gained about 15 mins per 24 hour period.

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Another anecdote, I recently had to replace a computer that had previously never been part of a domain. Imagine telling my client that it had to be replaced because it would not keep accurate time. He of course told me that he did not care if it kept accurate time, as long as it worked. Yeah.....try explaining time differentials and domains and Kerberos to someone who hired you to take care of all of that for him. – John3354 Oct 12 '12 at 2:00

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