The CPU

🧠 The decision maker

The CPU runs the instructions of every program: working out sums, moving data, deciding what happens next. In a game it tracks players and rules; in a browser it builds the page.

⏱️ Clock speed (GHz)

A CPU works to a beat called the clock. 3 GHz means about 3 billion beats per second, and on each beat it does a little work. More GHz can mean more work per second — but it's not the only thing that matters.

💪 Newer can be smarter

A newer CPU can beat an older one at the same GHz because it does more useful work on each beat (better design). Speed numbers alone don't tell the whole story.

👥 Cores and threads

A core is a worker inside the CPU. Many CPUs have several cores, so they can do several jobs at once. Some apps use many cores; others lean on one fast core.

🗄️ Cache: the near shelf

Cache is a small, very fast memory on the CPU itself. Grabbing data from cache is quicker than going to RAM, like keeping your most-used book on the desk instead of the shelf.

Key points

• The CPU runs the instructions of every program.
• It works to a beat called the clock, measured in GHz.
• 3 GHz is about 3 billion beats a second, doing a little work each beat.
• A newer CPU can beat an older one at the same speed — better design.
• A core is a worker inside the CPU; many cores do several jobs at once.
• Cache is tiny, very fast memory right on the chip.
• Grabbing from cache is quicker than going all the way to RAM.

Try it for real: Watch the CPU work

• Open Task Manager (Ctrl+Shift+Esc on Windows) or a system monitor, and open the CPU graph.
• Write down how many cores / logical processors it shows.
• Open a few programs and watch the CPU usage rise. Which activity used it most?