Presentation slides used to come in the 4:3 format. It was the standard even when we used mounted slides in a carousel tray. Nowadays, with the new HD televisions, 16:9 format is becoming the standard. The 16:9 format is better for smartphones and tablets and most conference rooms now use the 16:9 wide screens. If you’re planning an event that will require a screen, be sure to order the widescreen (or 16:9 screen) and make sure all of your speakers have their slides formatted for that aspect ratio.
Watch this video for a detailed explanation.