In 2007, a little over a month before the iPhone was scheduled to appear in stores, Mr. Jobs beckoned a handful of lieutenants into an office. For weeks, he had been carrying a prototype of the device in his pocket.

Mr. Jobs angrily held up his iPhone, angling it so everyone could see the dozens of tiny scratches marring its plastic screen, according to someone who attended the meeting. He then pulled his keys from his jeans.

People will carry this phone in their pocket, he said. People also carry their keys in their pocket. "I won’t sell a product that gets scratched,” he said tensely. The only solution was using unscratchable glass instead. "I want a glass screen, and I want it perfect in six weeks.”

After one executive left that meeting, he booked a flight to Shenzhen, China. If Mr. Jobs wanted perfect, there was nowhere else to go.

New screens began arriving at the plant near midnight.

A foreman immediately roused 8,000 workers inside the companyÂ’s dormitories, according to the executive. Each employee was given a biscuit and a cup of tea, guided to a workstation and within half an hour started a 12-hour shift fitting glass screens into beveled frames. Within 96 hours, the plant was producing over 10,000 iPhones a day.

For over two years, the company had been working on a project — code-named Purple 2 — that presented the same questions at every turn: how do you completely reimagine the cellphone? And how do you design it at the highest quality — with an unscratchable screen, for instance — while also ensuring that millions can be manufactured quickly and inexpensively enough to earn a significant profit?