It seems everyone is releasing an Android tablet this year. Unfortunately many tablets will not have access to the 70,000+ apps in the official Google market nor Google's own apps like Gmail and Maps and here's why.

The Android platform is open source which means that anyone can download, tweak and install it on any hardware of their choice. While this liberty is a wonderful thing, it puts the burden on third party developers to support an infinite range of hardware from toasters to servers. To alleviate this burden, Google set some requirements and guidelines for devices wishing to accessing the market in an attempt to standardize the target hardware.  These requirements are defined in the Android Compatibility Definition Document (CDD).  Unfortunately, the latest CDD as of now (2.2 Froyo) includes some restrictions that are not tablet friendly.

A few tablets will be able to access the market but those manufacturers seem to have made sacrifices in order to pass the compatibility tests.  Rumors are that the Gingerbread 3.0 CDD will include higher resolutions as well as other tablet friendly enhancements which means that some of these incompatible tablets may be able to access the market after an upgrade to Gingerbread but we won't know for sure until the 3.0 CDD is released.

Fortunately Google does not restrict Android to installing apps only from the official Google Android App Market nor do they restrict companies from running third party app markets. So, while users may not have access to the main app market they're still able to acquire apps from a number of alternate repositories.

Below are a few of the hardware incompatibilities that I noticed while browsing.This is not an exhaustive list and many of the device specifications are from unofficial leaks.