Getting Started: Flashing the OS
Before your Zero W can do anything, it needs an operating system on a microSD card. This lesson covers what you need to gather first and how to actually flash the OS image using the official tool. The next lesson builds directly on this one to get you connected over Wi-Fi and SSH with no monitor or keyboard ever required.
What You'll Need
| Item | Why |
|---|---|
| A microSD card | This is where Raspberry Pi OS and all your files live - there's no other onboard storage |
| A computer with an SD card reader (or a USB adapter) | Needed to write the OS image onto the card |
| A micro USB power supply | Plugs into the Zero W's dedicated power-only micro USB port |
| Either: a USB-to-micro-USB OTG adapter + keyboard, or a network connection | For interacting with the Pi directly, or for connecting headless over Wi-Fi/SSH instead (covered in the next lesson) |
Installing Raspberry Pi Imager
The official, recommended tool for preparing your microSD card is Raspberry Pi Imager, available for Windows, macOS, and Linux. It handles downloading the OS image, writing it correctly to the card, and - as you'll see in the next lesson - lets you pre-configure Wi-Fi and SSH before the card is even written, which is what makes a fully headless setup possible.
Choosing an OS Image: Lite vs Full Desktop
When you open Raspberry Pi Imager and choose an OS, you'll see options including a full desktop image and a "Lite" image. For the Zero W specifically, Raspberry Pi OS Lite is usually the better choice: it skips the desktop GUI entirely, which matters a lot on a board with a single-core CPU and only 512MB of RAM. Most Zero W projects - IoT sensors, headless services, camera projects - never need a graphical desktop at all, and Lite leaves far more of that limited CPU and RAM budget for your actual project instead of rendering windows you'll never look at. The full desktop image does exist and works on the Zero W, but expect it to feel noticeably sluggish given the hardware - it's better suited to boards with more RAM and more CPU cores.
The Basic Flashing Process
Once Raspberry Pi Imager is installed, the flow is straightforward:
- Open Raspberry Pi Imager and click "Choose OS" - select Raspberry Pi OS Lite (or Raspberry Pi OS if you specifically want the desktop).
- Click "Choose Storage" and select your microSD card - double check you've picked the right drive, since writing an image erases the card's existing contents.
- Before clicking "Write," consider opening the advanced customisation options - this is the crucial step covered in full in the next lesson, where you can set up Wi-Fi and SSH so the board never needs a monitor or keyboard at all.
- Click "Write" and wait for Imager to download (if needed), write, and verify the image.