Android tablets are very similar to Android mobile phones. The main specification difference between an Android phone and an Android tablet is the physical size and screen resolution. Generally, Android tablets work on lower PPI than a mobile. However, there is no hard-and-fast rule or any specific system to measure that.
The minimum requirement to run Android was a 200 MHz processor, 32 MB RAM, and 32 MB disk space. Android requires an ARMv5 or higher processor, although Android 4 requires ARMv7. Previously, starting age tablets had almost the minimum hardware system.
Tablets evolved from the concept of a tablet computer; they consist of a touchscreen display, camera, microphone, speaker, and a few physical buttons. Tablets are typically larger than phones or PDAs.
One of the minimum configured Android tablet is Coby Kyros MID7047, which is shown here (image source: http://www.evisionstore.com/catalogo/coby_mid7012-4g.jpg):
