Apple has recently sent out invitations about a special event on March 7th, which has little information, except for a tease that reads, "we have something you really have to see. And touch. 　　" The iPad range, which was first introduced in 2010, has sold over 50 million units worldwide. But iPad is not alone in this battle. Other challengers have stepped up, including the Kindle Fire by Amazon, which is sold at half the price of an iPad.