While some things about computers are “virtual,” they still must operate in the physical world and cannot ignore the challenges of that world. Rear Admiral Grace Hopper (one of the most important pioneers in our field, whose achievements include creating the first compiler) used to illustrate this point by giving each of her students a piece of wire 11.8 inches long, the maximum distance that electricity can travel in one nanosecond. This physical representation of the relationship between information, time, and distance served as a tool for explaining why signals (like my metaphorical sign above) must always and unavoidably take time to arrive at their destinations. Given these delays, it can be difficult to reason about exactly what “now” means in computer systems.
There is no now
2015-03-11 Hardware 10 Comments
Although you can’t really define “now” – you can timestamp things as having happened at an agreed UTC moment. You can also schedule for things to occur at a particular wall-clock time in a given time-zone (Long form) without knowing at the present time when that will actually transpire (since a leap second might be declared or a time zone alteration occur in the middle) – but once that time has occurred, you stamp it as having occurred at that moment, UTC.
Factoid: Electrons in the CERN LHC proved that electrons can move faster than that. 0.999999991c, or about 3 meters per second slower than the speed of light (c)