•The original iPad and iPad 2 models share the same 9.7-inch multitouch "glossy" LED-backlit IPS display, and width and height are similar

•Depth is different as the original iPad is 0.5 of an inch thick and the iPad 2 is 0.34 of an inch thick. 

•The iPad 2 is lighter 

•The original iPad only was offered in black while the iPad 2 was offered in black or white. 

•Both lines have aluminum backs. 

•The original iPad line lacks cameras entirely whereas the iPad 2 models have front and rear mounted cameras. 

•Both iPad models have 16 GB, 32 GB, or 64 GB capacity options, have 802.11a/b/g/n Wi-Fi, an accelerometer, an ambient light sensor, digital compass, a speaker and a built-in mic. 

•The original iPad models are powered by a custom ARM-based 1 GHz Apple A4 and have 256 MB of RAM and the iPad 2 models are powered by a faster, dual core 1 GHz Apple A5 and have 512 MB of RAM. 

•Both lines have an estimated battery life of 10 hours of use over Wi-Fi and 3G-capable models are estimated to provide 9 hours of runtime over 3G.

•The rear camera on the iPad 3rd Gen line is higherquality. 

•The iPad 2 models have a 0.7 megapixel camera that shoots stills and is capable of recording 720p video, whereas the iPad 3rd Gen models have a 5 megapixel "iSight" camera capable of shooting 1080p video.

•The iPad 3rd Gen also supports Siri when running iOS 6 or later, whereas the iPad 2 does not. 

•The iPad 3rd Gen is slightly thicker -- 0.03 of an inch -- and about a tenth of a pound heavier. 

•The iPad 3rd Gen models are powered by a dual-core 1 GHz Apple A5X processor with quad core graphics whereas the iPad 2 models have an older dual-core Apple A5 processor with a single graphics processor. 

•iPad 3rd Gen models have 1 GB of RAM whereas the iPad 2 only has 512 MB of RAM.

•Connectivity is substantially different. 

•The iPad 3rd Gen models also support Bluetooth 4.0 whereas the iPad 2 models support the earlier Bluetooth 2.1+EDR standard.

•the iPad 4 packs Apple's latest A6X processor, which Apple says "doubles the performance of CPU tasks. 

•The big difference between the two iPad generations lies within their connectivity options. The most obvious of these is the new 8-pin Lightning dock, first announced on the iPhone 5.

•The other major difference is that the iPad 4 comes LTE enabled.