FORTUNE -- Apple's (aapl) share price went on a tear Monday, gaining $17.04 a share (2.63%) to close at $665.15 -- a new high.
With 937.41 million shares outstanding, that put its market cap at $623.52 billion -- which if you don't factor in inflation is a record for a publicly trading company.
The previous record holder was Microsoft (msft), whose market cap hit $618.9 billion on Dec. 30, 1999. Adjusted for inflation, according to the AP, that's about $850 billion in today's dollars. Microsoft is currently valued at $257.6 billion.
The chart at right shows the two stock's performances over the past decade. You have to look closely to see Microsoft (represented by the green line at the bottom) because compared with Apple, its share price has basically flatlined.