Five. Weeks.

That's how long it took to write the operating system for the Apple II.

I've spent longer than that tracking down single-character logic errors.

Oy.

The total cost?  $13,000.

Talk to just about anyone intimately familiar with the Apple II, and one thing you'll hear often is that the disk controller Wozniak designed over the 1977 Christmas holidays for the computer was a proverbial game changer... 

But no matter how great its disk controller was, Apple had no DOS. Or any way to build one of its own. "They looked around Apple," Damer said, "and no one could write a DOS."

Obviously, they found someone to do it...

Although he knew little about operating systems, Wozniak is confident he could have built a good one. But his co-founder couldn't wait. "Steve Jobs, who didn't have patience for a project that took more than a week, found [Shepardson Microsystems] and...they sounded eager and knowledgeable...so we hired them." 

As then-Shepardson employee Paul Laughton remembers it, Wozniak came by one day saying Apple had a disk drive, but no DOS, and was wondering what to do. "I said, 'I know about operating systems.' And so he said, 'Cool, let's have you do it.'"