สาย Active vs Passive: เมื่อไหร่ที่มันสำคัญ

## Passive Cables

A passive cable is just wire and connectors — no electronics inside. They're cheaper, thinner, and work perfectly for short distances.

**When to use**: Runs under 2m at any speed. Up to 5m for USB 3.2 Gen 1 or HDMI.

## Active Cables

Active cables contain a **signal booster chip** (retimer or redriver) that regenerates the signal. This allows longer runs without data loss.

**When you need active**:
- USB 3.2 Gen 2 over 3m
- Thunderbolt over 2m
- HDMI 2.1 (4K@120Hz) over 5m
- DisplayPort 2.1 over 3m

## How to Tell

- Active cables are usually labeled as such
- They're more expensive ($30-80 vs $5-15)
- They're often slightly thicker
- Some are **directional** — there's a source end and a display end

## Fiber Optic Cables

For very long runs (10-100m), fiber optic HDMI and DisplayPort cables use light instead of electricity. They're expensive ($100+) but essential for conference rooms and home theater runs through walls.