As a young investment banker in the 1990s, Harry You learned about an obscure General Motors Co (GM.N) security called a ‘tracking stock.’ As an EMC Corp (EMC.N) executive working on selling the data storage company to Dell Inc, he helped revive it. The addition of a tracking stock for VMware, a software maker majority-owned by EMC, is a critical part of Dell’s $67 billion deal for EMC struck on Monday, the biggest technology acquisition ever if it goes ahead.