Understanding Epochs in Computing

What is an Epoch?

In computing, an epoch is a fixed point in time used as a reference for measuring time intervals. It serves as the "zero point" from which time is calculated in many computer systems and programming languages.

The most commonly used epoch is January 1, 1970, 00:00:00 UTC, known as the Unix epoch. This is used by Unix-like operating systems and many programming languages to represent time as the number of seconds that have elapsed since this reference point.

Why Epochs Matter

Epochs provide a standardized way to represent time in computer systems. Here's why they're important:

Epoch in Different Systems

While Unix epoch (1970) is most common, different systems use different epochs:

Working with Epoch Time in Code

Here's how you can work with epoch time in various programming languages:

// Get current epoch time in milliseconds
const now = Date.now();
console.log(now); // e.g., 1689876543210

// Convert epoch to Date object
const date = new Date(now);
console.log(date.toString()); // Human-readable date

// Convert date to epoch
const epoch = date.getTime();
console.log(epoch);

import time
from datetime import datetime

# Current epoch time in seconds
now = time.time()
print(now)  # e.g., 1689876543.21

# Convert epoch to datetime
dt = datetime.fromtimestamp(now)
print(dt)  # Human-readable date

# Convert datetime to epoch
epoch = dt.timestamp()
print(epoch)

import java.time.Instant;

// Current epoch time in milliseconds
long now = System.currentTimeMillis();
System.out.println(now);  // e.g., 1689876543210L

// Convert epoch to Instant
Instant instant = Instant.ofEpochMilli(now);
System.out.println(instant);  // Human-readable date

// Convert Instant to epoch
long epoch = instant.toEpochMilli();
System.out.println(epoch);