Packed Hazard in the sbc reward ! !!! So stoked ! Also got welbeck and Boufal . Definitely some nice profit <| sep |> There are actually about three clocks in a PC computer . All of them are based on a crystal oscillator which works because some materials are , which means they generate electricity when they are compressed , and they will change shape when an electrical current is passed through them . The most common material like this is quartz . When the crystal starts moving it will vibrate at a frequency that depends on the type of crustal , it ' s shape , the temperature , and even the direction of vibration of the crystal . The first clock is a lot like the clock in your watch . Its only counts in seconds , and it uses a a crystal that is shaped like a tiny tuning forkTuningfork . jpg . These crystals vibrate relatively slowly 32 , 000 times a second which generates an alternating current , a small circuit can then add a little push regularly to keep the vibration going . While these are quite sensitive to temperature changes , they are so popular that they have very good circuits attached to them that allow them to correct for this and be quite accurate . This clock also has a battery so it can remember the time even when the computer is off . The second clock is in the CPU . This vibrates faster 40 M times a second and the signal from it is sent to an electrical circuit called a phase locked loop PLL which then multiples this to get up to the actual CPU speed . This clock is very fast to read , amd can measure in microseconds , but it ' s relatively inaccurate compared with the one above . In some CPUs this clock is a count of the actual CPU cycles , but when a CPU goes into a power saving mode the CPU slows down so the clock slows down . In other CPUs this clock always runs at the same speed and the CPU has a different PLL for the actual instruction speed . This clock doesn ' t care about temperature much . It actually vibrates in two different directions at the same time , and these two vibrations respond to temperature changes differently , so by comparing them you can measure the temperature of the clock crystal itself and correct for it . The problem is that a slight difference in the crystal can cause it to have a slightly different frequency , so you generally have to calibrate this clock against one of the others if you want to be accurate over long times . Finally there ' s a clock that can generate interrupts . This is sometimes based on the same circuit as the first clock , but not always . Generally this can set a flag 8 , 000 times a second it ' s supposed to be anything from 2 k to 32 k , but most people don ' t actually build it this way . You can ' t actually read the time from this , but if you watch the flag and clear it repeatedly you can use it as a timer . The only odd detail about this is that it is intentionally inaccurate . If too many things on the computer all draw power at exactly 8 kHz , then it causes problems , so this clock alternates between running slightly slower and faster . Over time it ' s stable , but for less than a second it may not be as accurate . Some computers , or phones , have a GPS in them . A GPS works by knowing the time very precisely and measuring exactly where signals from satellites arrive . To do this the GPS receiver gets the time from the very accurate clocks in the satellites . This can take a few minutes to synchronize , but it ' s very accurate unless someone is jamming GPS and it can then be read by the computer . Finally there ' s NTP , or the network time protocol . That ' s a way for your computer to ask another computer what the time is , over the Internet . This tends to be a way to correct the time occasionally to keep it accurate .