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The original Raspberry Pi models launched were known as the Model A and the Model B (see Figure 1-2). Both had the same Broadcom BCM2835 SoC at their heart, but differed in specification: the Model A had 256 MB of RAM, a single USB port, and no networking capabilities; the Model B had either 256 MB or 512 MB of RAM depending on when it was purchased, two USB ports, and a 10/100 wired network port.

FIGURE 1-2: The Raspberry Pi Model B board

These models are immediately recognisable due to the smaller than normal GPIO port, which has only 26 pins compared to a modern Pi's larger 40-pin port. Both models also use full-size SD cards for storage, rather than the compact micro-SD cards of newer models. No longer manufactured, Raspberry Pi Model As and Bs are nevertheless still compatible with the majority of software designed for newer models but cannot use add-on hardware based on the HAT standard, as described in Chapter 16.

If you have a Raspberry Pi Model A or Model B, you can follow most of the material in this book without difficulty; simply pay close attention to sections such as Chapter 14, “The GPIO Port”, to ensure that you're not relying on information written with newer models in mind when wiring hardware directly into the Pi.