In the most obvious difference from its predecessors, the 4G iPod carries over the click wheel design introduced on the iPod mini. Some users criticized the click wheel because it does not have the backlight that the 3G iPod's buttons had, but others noted that having the buttons on the compass points largely removed any need for backlighting.

A horizontal blank interrupt is a programming technique used in some systems, notably video games and consoles, to allow program code to be run in the periods when the display hardware is turned off, waiting for the TV to complete its horizontal blank, which takes about 10 uS.


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