The menu entry uses 'a': "a USB startup disk" as does the first paragraph "install Ubuntu from a USB disk".
From wikipedia (http://en.wikipedia.org/wiki/A_and_an): "Ewe" and "user" have a preceding a because they are pronounced with an initial y consonant sound.
Try doing a search on google for "a USB" and "an USB" - "a USB" has nearly 20x the occurrences.
My locale is GB ;)
The menu entry uses 'a': "a USB startup disk" as does the first paragraph "install Ubuntu from a USB disk".
From wikipedia (http:// en.wikipedia. org/wiki/ A_and_an): "Ewe" and "user" have a preceding a because they are pronounced with an initial y consonant sound.
Try doing a search on google for "a USB" and "an USB" - "a USB" has nearly 20x the occurrences.