The billionaire donated 64 million of the software maker’s shares to the Bill & Melinda Gates Foundation on June 6, according to Securities and Exchange Commission filings released last month. The shares were valued at $4.6 billion at the time. It’s the largest gift of Microsoft shares that Gates, 61, has made since 2000. He gave away $16 billion worth of the stock in 1999 and $5.1 billion a year later, according to calculations by Bloomberg. Bill and Melinda Gates have given away about $35 billion of stock and cash since 1994, based on the value of the shares at the time of gifts, according to a review of Gates Foundation tax returns, annual reports and regulatory filings.