# Why Your Computer Is Slow

Your machine used to feel snappy and now every click comes with a little pause. The fan spins up to open a browser tab. You are eyeing a brand-new computer, or worse, dropping money on parts because a forum said so. Here is the relief: slowness is almost never mysterious, and you can usually fix it for less than a hundred dollars once you know which part is actually holding you back.

## How to read this

Read the three phases in order. The first gives you the one idea that makes everything else click: the bottleneck. The second teaches you to open the tool already on your computer and watch your machine confess where it hurts. The third turns those readings into a concrete buy-this decision and explains why one cheap upgrade beats the rest on most old machines. Try the readings on your own computer as you go; the whole point is that you can diagnose, not memorize.

## The phases

1. [The bottleneck: your computer is only as fast as its slowest link](01-the-bottleneck-mental-model.md)
2. [Reading the gauges: Task Manager and Activity Monitor](02-reading-the-gauges.md)
3. [The verdict: what to actually upgrade](03-what-to-upgrade.md)