In theory, Apple is a computer company. In practice, its most important product is a handheld computer called the iPhone, as this NYT piece makes clear.

Excerpt:

Toni Sacconaghi, an analyst at Sanford C. Bernstein, says the gross profit margin for the iPhone is close to 50 percent. Because the iPhone is Apple’s most popular product — with more than 39 million sold in the last quarter — it accounts for a disproportionately large percentage of Apple’s overall profit, somewhere between 60 and 70 percent, Mr. Sacconaghi said.

“Apple is now so big that it takes a lot to make it grow appreciably,” Mr. Sacconaghi said. It’s producing an impressive interrelated ecosystem of products and services, including its forthcoming digital watches, its new digital payment system, its revived Mac line, refreshed iPads and new software operating systems. Even if all of its ventures succeed, none are likely in the next year or two to rival the financial impact of the iPhone. “The iPhone is the core of Apple right now,” he said.

In a sense, it’s the core of the stock market as well. Apple is the biggest company, by market capitalization, in the world. Apple accounts for about 3.5 percent of the weighting of the Standard & Poor’s 500-stock index. And, through Thursday, because its stock has performed magnificently while the overall market has not, Apple accounted for 18 percent of the entire rise of the S.&P. 500 index this year, according to calculations by Paul Hickey, co-founder of the Bespoke Investment Group. And the engine driving Apple shares is the iPhone.