What a computer actually is

1. The promise

You'll be able to point at the four parts of any computer and explain in one sentence what each one does. You'll know roughly how fast each part is compared to the others, and which part your next purchase should focus on.

2. The mental model

A computer is a restaurant kitchen.

• The CPU is the chef. It does the actual work — every step of every recipe.
• The RAM is the prep counter. Small, but right next to the chef and instant to reach.
• The disk is the walk-in fridge. Huge, but a longer walk to get to.
• The network interface is the delivery driver. Orders and ingredients arriving from outside the building.

Carry this picture for the rest of the course. When a program is slow, you'll almost always be able to point at one of the four and say "that one."

(DIAGRAM: the four parts of a computer — annotated SVG — labelled boxes for CPU, RAM, Disk, Network connected by a single shared bus down the middle)

The four parts, said properly:

• CPU (central processing unit). The chip that does the computing. Modern CPUs run several billion small steps per second. Measured in GHz (gigahertz, billions of cycles per second).
• RAM (random-access memory). Fast, temporary memory the CPU works with directly. Measured in GB (gigabytes). Typical laptops have 8 to 64 GB. The contents of RAM vanish the moment power cuts.
• Disk. Long-term storage. Holds your files when the computer is off. Modern disks are SSD (solid-state drive, fast) or HDD (hard disk drive, slow, mostly extinct on new laptops). Measured in GB or TB.
• Network interface. The WiFi card or the Ethernet port. The part of the computer that talks to the outside world.

The speed gap between these four matters more than anyone tells you. If reading from RAM took one second, reading from a fast SSD would take about one minute, reading from a hard disk would take about an hour, and one round-trip across the internet to a server in another country would take roughly ten days. That gap is why programs are slow when they are slow, and why caching exists.

(CHART: relative speeds of CPU, RAM, SSD, network — horizontal log-scale bar chart — x-axis: latency in nanoseconds, bars labelled with the kitchen-analogy times "instant / one minute / one hour / ten days")

3. You do it, with me

Open the system info screen on your own machine. We're going to write down its four parts.

On macOS: click the Apple menu in the top-left corner → About This Mac.

(SCREENSHOT: macOS "About This Mac" window — full window — the "Chip" and "Memory" rows highlighted)

On Windows: open Settings (Win key, then type "Settings") → System → About.

(SCREENSHOT: Windows 11 Settings page — System → About — full window — the "Processor" and "Installed RAM" rows highlighted)

Take a piece of paper. Write down three rows:

1. CPU. Copy the name shown (e.g. "Apple M3 Pro" or "Intel Core i7-14700K"). The exact model doesn't matter for this course — we just want it on paper.
2. RAM. Copy the number in GB.
3. Disk. This one is on a different screen. On macOS, go to About This Mac → More Info → Storage. On Windows, go to Settings → System → Storage. Copy the total size in GB or TB.

For the network interface there's no number to copy — just write the connection you're using right now (WiFi or Ethernet).

4. What you should be seeing

A piece of paper with four rows on it. Each row has a label (CPU, RAM, Disk, Network) and the value from your screen.

The disk number is the biggest. The RAM number is the smallest. If yours look reversed, re-read the steps — you almost certainly wrote the wrong number on one row.

5. Common stumbles

• "My RAM and disk numbers look identical." They shouldn't. RAM is usually 8 GB to 64 GB. Disk is usually 256 GB to 2 TB. If they're close, you've copied one number twice — re-check the Storage screen for the disk.
• "My CPU name is full of letters and numbers I don't understand." That's normal. CPUs have model numbers like "M3 Pro" or "i7-14700K". You don't need to understand them. The chapter only needs the name on paper, not your interpretation of it.
• "GHz doesn't appear anywhere on the About screen." Some modern Macs hide it. Don't go looking — for this course, GHz is interesting trivia, not required information. The CPU's name is enough.
• "I'm on Linux." Open a terminal (you'll learn this properly in Ch 2) and run lscpu | head for CPU info, free -h for RAM, df -h for disk. Or use your distro's system-info GUI; every distro has one.

6. You should know