A Practical Guide to Time for Developers: Part 2 — How one computer keeps time (Linux)

Time on a computer looks simple: call now(), get a timestamp, move on. In the previous article , we discussed the idea that time is just a single point on a timeline. The crucial part is defining which timeline that point belongs to. For computers, this matters a lot. A system effectively works with two timelines: real time and boot time . You can convert between them, but they are different measuring systems and shouldn’t be used interchangeably—because each timeline serves a different purpose. Real time answers: “What time is it in the real world right now?” Boot time answers: “How much time has passed since X (boot)?” The computer has has an ecosystem - a few components: hardware and software to track and calculate different times in both timelines. This part explains that ecosystem using one diagram, top to bottom. The diagram is the spine; everything else is commentary that makes it click: where ticks come from, what the hardware pieces do, why there are multiple “system times”, w