There were doubting Thomases, but Apple proved them wrong in spectacular fashion when the iPad first went on sale in April 2010.

For years, the sales of consumer PCs had been pretty steady with few signs of decline. Not even when Microsoft released the clunker Vista. Not even when the economy crashed. 

But suddenly, the growth of sales is "about to go negative,"  Citi analyst Walter Pritchard has told Business Insider. And if you look at the chart, the turning point is  the iPad hitting the market in April 2010. 

Jobs said in his January  presentation, iPad in hand (pictured), that he thought there was a gap in the market  . "We need a third category of device, something between a phone and a laptop.Something that's better for gaming and browsing the web than an iPhone." Netbooks weren't better at anything. So, we needed a third category, the tablet.

There were many doubters. But by the end of 2010, the iPad had sold 14.8million. 

Today total iPad sales are over 19 million. There have been long lines to buy iPad2 and a flourishing  black market in countries where it is not yet on sale. Other manufacturers have rushed in but few have come close to the success of the iPad. And as the chart suggests, the biggest hit was the one taken by Microsoft, king of the computer castle.

Steve Jobs, genius of Apple and cancer survivor, we salute you. And look forward to what you have to say on Monday.