Input voltage question on Mega

Development Tools IDE 1.x
1

Hi.
I'm an Arduinoob! Looking at buying his first board.

One thing puzzles me.

The info the Mega says:
The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.

How then can it be powered stably by 5.5v coming from a comuter usb port?

Thanks.

2

Because the 5V from USB doesn't go through the regulator.
The schematics are available here

under each individual board's page.

3

Doh!!

Thanks, AWOL.

See, I'm learning already....!