The Model A/A+ has one USB port, the Model B has two ports, and the Model B+, Pi 2 Model B, and Pi 3 Model B have four ports. These can be used to connect most USB 2.0 devices. Additional USB devices such as mice, keyboards, network adapters, and external storage can be connected via a USB hub. The Pi Zero and Pi Zero W have a single micro USB port, this requires a USB OTG cable to connect devices such as keyboards or hubs.

You can check our [products](https://www.raspberrypi.org/products/) pages for more details on current boards. There are also some models of Raspberry Pi which are no longer in production, but which may be available second-hand or from resellers. The Model A was the initial low-cost variant of the Pi. It was replaced by the smaller, neater Model A+ in November 2014; it shares the same specs as the A+, but has only 26 GPIO pins and 128MB of RAM. The Model B was the previous incarnation of the B+; again, it shares most of the same specs, but has only two USB ports and 26 GPIO pins. The original version of the Pi Zero did not come with a camera connector, but all current versions have the connector as standard.