Steve Jobs Apple Shaken to Core CEO Resigns

8/24/2011 3:45 PM PDT

Apple Shaken to Core -- Steve Jobs Resigns

Hold on to your iPhones, iPads -- and most importantly, your Apple stock -- Steve Jobs is stepping down from his post as CEO.

Jobs handed in his letter of resignation today, but will stay on as the Chairman of Apple's Board of Directors. Tim Cook will be the new CEO.

Jobs has been on medical leave most of 2011-- and hinted at his continuing health issues in the letter ... saying, "I have always said if there ever came a day when I could no longer meet my duties and expectations as Apple's CEO, I would be the first to let you know. Unfortunately, that day has come."

Jobs co-founded Apple in 1976 -- and earlier this month it became the world's most valuable company.