"Microsoft will need to be bold and make big bets to succeed in this new environment," he told Nadella. "Our board must also support and encourage that fearlessness for shareholders to get the best performance from Microsoft. You must drive that." While he's no longer a voice within the company, Ballmer still cares about Microsoft's stock performance: outside of index funds, he still owns more Microsoft shares than anyone, he says. "I bleed Microsoft, have for 34 years and I always will," he concluded. "I promise to support and encourage boldness by management in my role as a shareholder in any way I can."

Nadella shot back a supportive, equally optimistic response, promising that Microsoft will thrive in "the mobile-first, cloud-first world." End of an era? For sure -- you can read the full, unabridged letter (and Nadella's response) at the source link below.

[Image credit: NBAE/Getty Images]