"... A+ is $20. It uses the same BCM2835 application processor and has the same 256MB of RAM, but it’s much smaller. Just 65mm long, compared to 86mm for the older Model A. It’s also more energy efficient, and gains many of the same improvements introduced in the Model B+ including:
- More GPIO -- The GPIO header has grown to 40 pins. The Model A+ is compatible with the HAT standard for add-on boards.
- Micro SD -- The old friction-fit SD card socket has been replaced with a much nicer push-push micro SD version.
- Better audio -- The audio circuit incorporates a dedicated low-noise power supply."
Raspberry Pi Model B+ and Model B Boards and Accessories | MCM Electronics