Source of historical intraday stock prices?
 

Is there a free source of historical intraday stock prices for a
given stock?

With bigcharts.com, I can chart intraday prices with 1-minute
frequency for up to the last 10 days.

I am looking for the raw data that feeds such charts.

I usually go to finance.yahoo.com to download historical quotes
in Excel format. But the best that provides is daily frequency.